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Photo Forum / Film Photography / Medium format / November 2003Zoom vs. fixed focal length
Generally speaking, do you sacrifice performance with a zoom lens compared to a fixed focal length lens? Specifically, the Pentax 67, 55-100mm f/4.5 compared to the 67 fixed focal length lenses? Thanks all!  SignatureRay ( www.rayspace.com ) ------------------------------------------- "I'd rather wake up in the middle of nowhere, than in any city on earth" - Steve McQueen I think that the answer is usually yes, but not always, and usually not a lot. I've got Canon EOS 28-80, metal mount which is a superb zoom, very sharp etc. However the 50 f1.8 and 28 f2.8 are a little crisper in shots in which I've used them. But you will have to look for the little improvement. > Generally speaking, do you sacrifice performance with a zoom lens compared > to a fixed focal length lens? Specifically, the Pentax 67, 55-100mm f/4.5 > compared to the 67 fixed focal length lenses? I think it depends on the vintage of the design. The older zooms left something to be desired while the newer designs work pretty good. SignatureStacey Thanks Stacey :-) > I think it depends on the vintage of the design. The older zooms left > something to be desired while the newer designs work pretty good. > Generally speaking, do you sacrifice performance with a zoom lens compared > to a fixed focal length lens? Specifically, the Pentax 67, 55-100mm f/4.5 > compared to the 67 fixed focal length lenses? The main difference is usually optical power. No MF zoom can beat a fixed lens around f:2, because no MF zoom has f:2 to offer ;-) -- Lassi there are only a handful of f/2 and faster lenses in medium format, so the typical speed of f/2.8 or f/3.5 at maximum aperture is only modestly faster than many MF zooms. There are some unusual fast lenses and zooms for medium format use (bronica mount) described by Simon Nathan and summarized at: http://medfmt.8k.com/bronlens.html#simon - including an MF zoom lens (110-160mm f/3.5) made from a slide projector lens. Since there are lots of low cost slide projector zoom lenses, many which can evidently cover MF, it might be a useful source of lenses for lens hacking a MF zoom missing or unaffordable in many lineups (at least for focal plane cameras?)... see http://medfmt.8k.com/brontenmyths.html myth #31 - the 35mm SLR makers lenses MTF scores suggest that the _average_ zoom is nearly a full level (1 in 5) poorer performer than the average fixed focal length lens. There are lots of so-so consumer zooms with bad distortion and poor closeup performance vs. fixed lenses, and the few pro quality zooms often cost more than three or more fixed lenses they replace ;-) You both pay and sacrifice a lot for the convenience of the zoom lenses, but probably 90% of the lenses being sold to amateur photographers are zooms today... bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* >see http://medfmt.8k.com/brontenmyths.html myth #31 - the 35mm SLR makers >lenses MTF scores suggest that the _average_ zoom is nearly a full level [quoted text clipped - 4 lines] >sacrifice a lot for the convenience of the zoom lenses, but probably 90% >of the lenses being sold to amateur photographers are zooms today... The Canon 28-70 L gets higher ratings than a lot of primes in the ranges it covers -- including Nikkors and Canon L primes. The reasons for using zooms are obvious, at least in situations where speed, weight or convenience or price are of any concern. If you're shooting in a studio, or if you have an assistant to schlep your gear, or you have multiple camera bodies each with a different fixed prime attached -- that's great. But amateurs typically don't operate under any of those conditions. rafe b. http://www.terrapinphoto.com However, given that MF is superior to 135 format, perhaps the MF zooms are proportionally better. > >see http://medfmt.8k.com/brontenmyths.html myth #31 - the 35mm SLR makers > >lenses MTF scores suggest that the _average_ zoom is nearly a full level [quoted text clipped - 20 lines] > rafe b. > http://www.terrapinphoto.com >However, given that MF is superior to 135 format, perhaps the MF zooms are >proportionally better. I imagine most of the same principles apply. Optics are optics. If anything, MF lenses have more area to cover, and that's an additional technical challenge. Are there any equivalents in the MF world to Canon L series or Nikon ED glass? I mean, stuff like low dispersion glass, aspheric elements, image stabilization, and so on? I had a browse over on the Zeiss web site and saw no mention of these technologies used in their MF lenses. rafe b. http://www.terrapinphoto.com sure, see http://medfmt.8k.com/mf/hassylenses.html - zeiss has an APO lens series for hasselblad for example, even more $$ than the regular zeiss MF lenses ;-) better performance, but as the above URL notes, most users would be challenged to improve their technique to get the maximum performance out of these lenses in actual day to day use. re: zooms, above URL has a (bizarre) lens test for the hasselblad schneider zoom - I say bizarre because the 140-280mm zoom outperformed the fixed zeiss lenses by scoring up to 91 lpmm in the center - and an abysmal 29 lpmm in the edges at 280mm - oops! ;-) The chart comparing the 150mm f/2.8 F series lens against the zoom shows the zoom is competitive in the center resolution, but clearly inferior in the edges. That's a $4,000 ish zoom! ;-) I also take issue with your 35mm zoom vs. fixed lenses points earlier; zooms generally lose out on speed and weight and cost if of pro quality. Others have noted that you can buy a set of (faster and equal or better quality) canon fixed lenses for less than the canon top line wide angle zooms cost, and ditto for nikon IIRC. Zooms are more convenient for many users and action situations, but I find them heavier on the camera, and accessories like filters can cost a whole lot more for larger filter size zooms etc. Most of us don't carry every possible lens in a zoom's range (e.g., not 70, 90, 105, 135, 180 and 200mm lenses for a 70-210mm zoom, but maybe a 100mm macro or 105mm f/2.5 and a 180mm or 200mm f/4. In most cases, the carrying weight may be the same (or less), but the weight on camera and pulling on the neck strap is usually a lot less with fixed lenses than a typical fast zoom ;-) !! Finally, for those of us who can't afford or don't need the convenience of zooms, the fixed lenses (esp. used) are often terrific bargains for their high quality optical performance and speed. ANd in medium format, where quality is the major factor, zooms are generally not optically equal to the fixed lens alternatives as lens testing has shown... regards bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > sure, see http://medfmt.8k.com/mf/hassylenses.html - zeiss has an APO lens > series for hasselblad for example, [...] Bob, you seem to have trouble keeping Apochromats and Superachromats apart. I have told you once before... ;-) There are no Zeiss Apo lenses available for Hasselblad anymore. The 500 mm Tele-Apotessar was the only one. Apochromatically corrected lenses are lenses that bring three colours to a common focus. The secondary spectrum is then usually very close, very good, but not necessarily so. Chromatic abberation still exists, and in many apochromatic lenses is still present in significant amounts. In Superachromatically corrected lenses *all* wavelengths are brought to a common focus. There is no secondary spectrum: the focal length for all wavelengths is so close that the degradation caused by remaining chromatic aberration (nothing is perfect, ever) are well below the level of any other aberration, i.e. does not affect image quality any more. To all intents and purposes, chromatic aberration is gone completely. Zeiss has a series of superachromats for Hasselblad. But no (!) apochromats. yes, you keep reminding me ;-) But the answer remains yes, even zeiss has some high end lenses which are even better than their regular series, and a lot more costly ;-) And if a lens is a "superachromat", then it must also be at least an apochromat, yes? ;-) the problem here is partly that there are NO precise definitions of when a lens is or is not Apochromatic, and the term superachromatic is even less familiar (a zeiss invented term?), at least as far as photo lenses goes (that is not true of things like eyepieces where there are precise DIN style definitions for apochromatic performance, I'm told). Zeiss may have their own terms and definitions, but in my view it verges on marketing hype. You need to have that "super" in the lens name to justify the super-prices, yes? ;-) ;-) One reason for this definitional caution is that we are seeing a series of not very stellar zoom lenses which are being touted as apochromatic optics. They can be marketed as such without being such, since there isn't any legally accepted standard in the photographic lens industry for that term (at least, here in the USA). The ones I tried had more color fringing than my 25 year old non-APO vivitar series I telephotos ;-) This is unfortunate, as we can no longer rely on elements like low dispersion glasses or claims of apochromatic performance to be reflected in lens performance. This may be one reason that Zeiss has chosen superachromat rather than super-APO? ;-) grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > yes, you keep reminding me ;-) But the answer remains yes, even zeiss has > some high end lenses which are even better than their regular series, and > a lot more costly ;-) And if a lens is a "superachromat", then it must > also be at least an apochromat, yes? ;-) Yes. But you actually do bother to use the term apochromat, don't you? Why is that? Why not just say achromat, for apochromats must be at least achromats too...? > the problem here is partly that there are NO precise definitions of when a > lens is or is not Apochromatic The terms are commonly used and understood (!) to distinguish between the different degrees of correction. And the "two colours = achromat", "three colours = apochromat" and "all colours = superachromat" "definition are precise enough. You mention the Apo-hype. That would not, could not even, exist if we poor saps did not have a (more or less) clear idea of what all these terms mean. Could it? See? What in each is not defined is how close "the other" colours are in focal length to the focal length of the two, or three, chosen to have a common focal length. Undefined, except in the case of superachromats, of course, since there are no other colours... Apochromats "work" because when three colours are corrected, the correction of other colours "in between" "usually" is very close "automatically", i.e. without extra effort or attention. But remember Murphy's law? So some apochromats are very good, but some are not (though they still are real apochromats. We've not reached the "apo-hype" yet.). In superachromats, the effort to ensure that the secondary spectrum is reduced to insignificant levels is made. Unlike with apochromats, this is not left to chance. So "real" apochromats and superachromats represent two very different classes of lenses. To call "superachromats" "apochromats" is, at best, confusing. Certainly so in the present context, where the better performance is set against the inability of most photographers to match this performance with their technique. >, and the term superachromatic is even less > familiar (a zeiss invented term?) Less familiar, because there are very few lenses that have that type/degree of correction. (And one can ponder why that is at length. For instance, if we do really need such lenses or not. Or whether it makes any sense at all to make such things available to "photographers" who pride themselves for handholding at 1/15. Etcetera.) And yes, it's a Zeiss invented term (and thing) too. They were the ones first achieving that degree of correction in a lens. And at the time, they made very clear what the term they coined meant. Asahi Pentax is, as far as i know, the only other manufacturer that built lenses with the same degree of correction. They called their's "Ultra-achromatic". I'm not 100% sure, but i think they stopped producing these lenses. If so, the only superachromats available indeed are the ones carrying the label "superachromat" (though there was one made for Hasselblad too that was not called superachromat: the UV-Sonnar). But don't blame Zeiss, nor the lenses, for people not being familiar with the phenomenon/term. >, at least as far as photo lenses goes > (that is not true of things like eyepieces where there are precise DIN > style definitions for apochromatic performance, I'm told). Zeiss may have > their own terms and definitions, but in my view it verges on marketing > hype. You need to have that "super" in the lens name to justify the > super-prices, yes? ;-) ;-) Maybe. But as fas as the Zeiss Superachromats go, the "super" bit actually means something. There is a corresponding "reality" in need of a name, it is not an empty phrase. Superachromats' performance actually is "above" that of other, non-superachromatically corrected lenses. Try one, and you'll see. > One reason for this definitional caution is that we are seeing a series of > not very stellar zoom lenses which are being touted as apochromatic [quoted text clipped - 7 lines] > in lens performance. This may be one reason that Zeiss has chosen > superachromat rather than super-APO? ;-) No. The Apo-hype was yet to happen when they built and named their first superachromat. Yes, unfortunately there is indeed an Apo-hype. Teaches us not to do business with manufacturers who employ labelling tricks. However, it's not their fault. That they do, in turn, is a reflection of how many of us are not prepared to educate themselves about what they are putting money towards, but/and are willing to be fooled by labels. Pure, unadulterated consumerism. Also known as idiocy. But some respectable lens manufactureres (and there still are a few) don't play that game. We can still rely on their labelling. But how is the fact that some lens manufacturers play the suckers among us for what they are an excuse for not using the proper name for the proper (and very real) quality? ach, my head is exploding ;-) All these terms - achromats, anastigmats, apochromats, superachromat, ultrachromatic. And all of them mean just what the mfgers say they do; and they're all right, even if they aren't consistent, since there are no recognized international standards defining these terms for the consumer photo industry (by industry design? ;-) part of my issue with "superachromatic" is that it uses achromatic instead of apochromatic. Simple logic would suggest that the correct sequence is: achromatic, superachromatic, apochromatic, superapochromatic,ultra-super... do you see my issue here? if achromats correct two frequencies, and apochromatics correct three color frequencies to zero, then anything which corrects even more frequencies should be a superAPOchromatic lens, not a superACHROmatic lens ;-) ;-) so the logical sequence is: achromatic, apochromatic, superapochromatic or ultra-apochromatic lenses.. as you noted, a related problem is that many of the UV (quartz) lenses may provide great correction from shortwave UV to IR, let alone the visible color range. So we also have another class of lens which is not a superachromat but which has ultra-superachromatic performance ;-) Not just visible light, but longwave and shortwave UV and IR to boot ;-) So aren't these UV lenses really a super ultra UV apochromatic lens? ;-) Does a super-ultra UV apochromatic lens beat a superachromatic lens? ;-) to me, a superachromatic lens should be a lens which does a super job of bringing two colors to the focal plane, not all colors, right? ;-) And as far as I know, there is no guarantee which two or three colors will be used, though some sort of red/green and red/blue/green seems implicit ;-) I mean, it could be red and pink and orange, based on some "APO" zoom lenses I've seen lately? Again, seems to be undefined for photo lenses... I'm guessing that zeiss has a service or trademark on the term "superachromatic", and pentax on "ultra-achromatic"? ;-) So every mfger who wants to push their lenses for maximum $$ simply has to trademark their own confusing super or ultra something or other to get us confused. somehow, I suspect that somebody else has a trademark on the term superapochromatic (perhaps nikon? canon? ;-), and that pentax as you noted has "ultra", so zeiss marketing types went for the superachromat label as it wasn't trademarked, rather than it was what the lens really was/is? ;-) This has an Alice in Wonderland quality about it - photo industry terms mean what the mfgers say they mean, they don't mean what you would logically think they mean, and each mfger is out there inventing their own ;-) It may be that zeiss is specifying what their terms mean publicly, but how many people ever look that up, let alone understand it like you do, QGB? ;-) But the serious point remains that many low cost lenses (APO zoom 200-600mm) turn out to be the same old lenses, but with marketing hype. And I think the need to hype the high $$ lenses is related to creating a desire for these fine zeiss optics in those who can afford them, even if they don't need and don't have the technical ability to take advantage of these refinements? That said, I agree with you that the performance of these zeiss lenses is spectacular. The problem you hinted at is that you have to use great technique to take full advantage of such stellar lenses, including very fine grain high resolution films, very sturdy tripods (plural intended), stable air mass conditions, and so on ;-) I am not pushing the limits of my current zeiss (or other) lenses with my current technique, so I can't justify the $$ nor create a "need" for such stellar optics (but rentals might be fun ;-). grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > . . . . many of the UV (quartz) lenses may > provide great correction from shortwave UV to IR Just a note on this: quartz alone makes a very poor wideband lens, and is in fact used in the high dispersion "flint" elements in UV-VIS hyperspectral apochromats. There have been some all-silica lenses built for deep UV photolithography, but these were intended for narrow-band laser illumination. Also, if you extend correction down to the deep UV (~ 250nm) then in my experience you can't get longwave correction beyond about 650nm (red). Coastal Optical currently makes a lens of this type: http://www.coastalopt.com/stan_02.asp Moderate UV to IR apochromatic correction is possible, however (350nm - 2000nm). Brian www.caldwellphotographic.com Thanks, Brian, for the URL and notes; I am glad to see a nikon mount replacement for UV-nikkor, esp. a 105mm f/4 UV macro lens. They also have some interesting papers on alignment testing etc. the hasselblad UV-sonnar 105mm f/4.3 works down to 215 nm, but they claim it will work not only for regular visible light but even IR photography up to 700 nm, (but evidently using filters, so probably not continuous apochromat performance over the entire range, as you noted ;-( regards bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > part of my issue with "superachromatic" is that it uses achromatic instead > of apochromatic. Simple logic would suggest that the correct sequence is: [...] Simple logic doesn't come in to this. Manufactureres were so pleased when they made what now are called apochromatic lenses that they boasted that all colour faults were gone (apo = away, gone, no more). Of course, that was a bit too optimistic. So what to call the next better lenses? What is the word that cam express less than "apo", less than "nothing"? The same proble arose before, when they invented lenses that were better than achromats. "A" in achromat indicating a blanket denial of the existence of any chromatic fault already. So a new term was coined. Zeiss went for "superachromatic", a strange thing at best, since it implies there is even less chromatic aberration than the "none" "a"chromatic implies. Pentax went for yet another "definitive" term: Ultra-achromatic, which in itself suggests there can not be any better. Well chosen? True? May well be, yes. > so the logical sequence is: > > achromatic, apochromatic, superapochromatic or ultra-apochromatic lenses.. Nope. There is no logic in "apo" following "a". So you'd better abandon the notion that logic is involved at all. > as you noted, a related problem is that many of the UV (quartz) lenses may > provide great correction from shortwave UV to IR, let alone the visible > color range. So we also have another class of lens which is not a > superachromat but which has ultra-superachromatic performance ;-) Not > just visible light, but longwave and shortwave UV and IR to boot ;-) [...] Take care not to fall into another confusion. Lenses can be corrected to have the same focal length for, say, only two focal lengths (achromats). One of these may fall into the IR or UV part of the spectrum. That however says absolutely nothing about what the focal lengths in between do... And an apochromat may be corrected for three wavelengths, one in the UV part, the second in the green part, and the third in the IR part ofthe spectrum. But what do we then know about what the wavelengths in between do...? The "superachromatic" quality says something about the secondary spectrum (the "wavelengths in between"). Not the part of the spectrum a lens is corrected for: but how all wavelenghts in the chosen range "behave". The Sonnar-Superachromat 250 mm, for instance, is superachromatically corrected for all wavelengths between 400 nm and 1000 nm. You can focus using visible light, and take pictures using the IR part (upto 1000 nm) only, without needing to adjust focus. The other Superachromats do not have this extended range. They are superachromats in the "normal" range of visible light. > to me, a superachromatic lens should be a lens which does a super job of > bringing two colors to the focal plane, not all colors, right? ;-) No. Wrong. ;-) > And as far as I know, there is no guarantee which two or three colors will > be used, though some sort of red/green and red/blue/green seems implicit > ;-) I mean, it could be red and pink and orange, based on some "APO" > zoom lenses I've seen lately? Again, seems to be undefined for photo > lenses... Indeed. > I'm guessing that zeiss has a service or trademark on the term > "superachromatic", and pentax on "ultra-achromatic"? ;-) So every mfger > who wants to push their lenses for maximum $$ simply has to trademark > their own confusing super or ultra something or other to get us confused. That, at one time, was true of now generic terms like "retrofocus", "achromat", "anastigmat", "apochromat", etc. too. > somehow, I suspect that somebody else has a trademark on the term > superapochromatic (perhaps nikon? canon? ;-), and that pentax as you noted > has "ultra", so zeiss marketing types went for the superachromat label as > it wasn't trademarked, rather than it was what the lens really was/is? ;-) [...] Well, seeing that Zeiss was the first (!) manufacturer to produce lenses that needed a new term, i don't think other manufacturers already had laid claim to their own. But anyway... ;-) The thing to remember is that it is not about the name they happened to pick, but that this name (whatever it may be) is really indicating a quality these lenses have, and others do not. The thing to remember is that this is not another example of marketing hype. I for one couldn't care less how they call this quality, i know that i'd rather have the Sonnar-Superachromat than the bunch of 250 mm lenses i have know. The superachromat is very, very much better. And that's what matters, doesn't it? The matter about whether or not we "need" to spend money on this extra quality is quite another thing. Whatever our (personal) answer may be, it does not change the fact that these superachromatic lenses do have this extra quality. Which still means they merit the use of the term that was invented (no matter how (il)logical) for them. So don't continue "insulting" them by calling them "apochromats"... ;-) My answer? No, i don't need it, most of the time. But i certainly could use that extra bit sometimes. And apart from that, i *like* the extra bit, even when i don't need it. It is like soft focus lenses: you can soften a sharp lens, but you can't sharpen a soft lens. So i'd better have too much of something than too little. Yet "reason prevails". Which is another way of saying i can't find the "green stuff" to get one. There's always something else that makes more sense. ;-) ah, good answers as usual, but raising some more questions, also as usual ;-) for example, if only the sonnar superachromatic 250mm has an extended range down into the IR range w/o changing focus from visible light, shouldn't it be a "super" super achromatic 250mm? or maybe a hyper-achromatic lens? ;-) ;-) Isn't it a lot more super than the other super-achromatic lenses which only cover visible light ranges? ;-) I agree with you now that logic fails me, esp. given your point that achromatic means no chromatic aberration - so they should be at least as good as the super achromats, and if apo ~= no or none, then if the lenses were true to their descriptions we wouldn't need any of the extra categories ;-) Even the implied 2 (achro) and 3 (apo) corrections are an issue, as I noted, since we don't know how good the nulls are, or where in the color range they fall etc. But if you are spending the extra $$, esp. for superachromats, I presume you will have satisfied yourself that the extra performance warrants the extra costs ;-) unfortunately, I fear the marketing types will pervert the meanings of lens quality terms to mean nothing, leaving us to have to review tests or MTFs etc. of the lenses to learn what and how they really perform ;-) I personally would prefer NOT to have the superachromatic lenses; they would only make me feel guilty about not using their full potential, and paranoid about taking them into situations where they could be damaged or lost or stolen - which is a lot of the kinds of places I shoot ;-) Roger Hicks wrote an article about situations where the best lenses won't do, you want the not so good ones which are good enough, or to start out on a budget etc. ;-) I cited another unrelated issue where the most pricey lenses are not as good as the cheapies for specific services such as macro photography, where slower and simpler lenses are often better in use. The more I study lenses, the more surprised I am at how good most med fmt lenses are for the vast majority of situations I photograph. Fortunately, I didn't know this starting out, so I got to buy into and try out a lot of fun gear ;-) ;-) Sometimes it is also better to be ignorant than informed! regards bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > [...] for example, if only the sonnar superachromatic 250mm has an extended > range down into the IR range w/o changing focus from visible light, > shouldn't it be a "super" super achromatic 250mm? or maybe a > hyper-achromatic lens? ;-) ;-) Isn't it a lot more super than the other > super-achromatic lenses which only cover visible light ranges? ;-) No. It should be called something like Sonnar-IR-Superachromat. ;-) The degree of correction is the same (hence "superachromat"). It's just over a wider band. > [...] But if you are spending the extra $$, esp. > for superachromats, I presume you will have satisfied yourself that the > extra performance warrants the extra costs ;-) Why, yes. And not only the extra performance of the lens should be considered. > unfortunately, I fear the marketing types will pervert the meanings of > lens quality terms to mean nothing, leaving us to have to review tests or > MTFs etc. of the lenses to learn what and how they really perform ;-) Well... Maybe... Maybe not all? > I personally would prefer NOT to have the superachromatic lenses; they > would only make me feel guilty about not using their full potential, and > paranoid about taking them into situations where they could be damaged or > lost or stolen - which is a lot of the kinds of places I shoot ;-) Well, it's like those soft-focus thingies. I'd rather have a sharp lens that i can soften, even if i need/want to/will do just that most of the time. Leaves me with the choice of taking all due care once in a while and get that extra bit i couldn't get no matter what i'd try with another lens. And you're not saying you're one of those unfortunate people suffering from the "too-expensive-to-take-out-of-the-box"-syndrome? It's only money, isn't it? ;-);-) > [...] Sometimes it is also better to be ignorant than informed! Yes. So you can learn and end up being informed. ;-) re: leave it in the box syndrome? no, I'm one of those who can't afford the boxes ;-) see nikon SP camera box (not the camera, just the box for it) sold for $685 on EBAY - note at http://medfmt.8k.com/mf/beat.html Beat This! Ridiculous Prices for Photo Gear ;-) Makes me wish I _had_ kept those boxes (and those old comic books, and ... ;-) I am a bit more careful with my SWC/M than I am with my kiev60, and my nikkormat kit than my nikon F2 etc. I have a "graffitti" kit for shooting in high risk areas (theft etc.). But I'm always amazed to buy a "used" camera (35mm usually) in which there is virtually no wear from lack of use. The flip side is some of my stuff is a bit worn (180mm etc.); on a past phototrip with one of the local clubs, I was asked all kinds of questions about new cameras - somewhat illogical, since I had the oldest kit on the bus, but the newbies looked at each other and saw brand new gear and no visible wear or use, so turned to me as someone who obviously had shot a lot of film to ask how their brand new cameras worked (RTFM ;-) re: soft lenses I have some of those soft lenses; my problem is they aren't soft enough when you stop down to get good DOF ;-) Nearly all of the soft lenses, even the dang +10 diopter single element lens SIMA-Soft gizmo, will yield surprisingly sharp photos stopped to f/8 or so, it is quite horrifying ;-) On large format, Feininger used an office magnifying glass to generate a huge but very good looking image when stopped down for 20x24"; of course, a contact print doesn't need much enlarging ;-) I have a 50mm f/40 (!) panfocus lens; here you get softer courtesy of diffraction limits, but there isn't a lot inbetween that is really soft at f/8 to f/16 ;-) grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > Nearly all of the soft lenses, > even the dang +10 diopter single element lens SIMA-Soft gizmo, will yield > surprisingly sharp photos stopped to f/8 or so, it is quite horrifying ;-) Yep I "made" a soft focus lens out of a junk 80mm biometar using only the front element stuck back into the lens housing just in front of the diaphram and at f8 and smaller is amazing how sharp just one lens element is! SignatureStacey > . . . . . . > [quoted text clipped - 3 lines] > even the dang +10 diopter single element lens SIMA-Soft gizmo, will yield > surprisingly sharp photos stopped to f/8 or so, it is quite horrifying ;-) You must have made your own f8 stop, since the SIMA did not come with one. Wide open, it is f2. There are two disk stops of f4 and f5.6 value, and an ND filter that fits behind the front bayonet mount. At f5.6, there still is a decent soft focus effect. Anyway, this SIMA is not high quality, and the look is a bit strange. The Macro ability is even stranger, and not being able to stop down smaller than f5.6 means that flowers could look like a blurry mess. Better to leave the SIMA in the abstract imagery realm. > On large format, Feininger used an office magnifying glass to generate a > huge but very good looking image when stopped down for 20x24"; of course, > a contact print doesn't need much enlarging ;-) I have a 50mm f/40 (!) > panfocus lens; here you get softer courtesy of diffraction limits, but > there isn't a lot inbetween that is really soft at f/8 to f/16 ;-) Then there is always that silly new filter in the latest PhotoShop. You can blur the selected area, and even choose shapes for the highlights in the defocus areas. It attempts to mimic aberration blurs, though it is all at once, rather than gradual change over distance. I can just imagine seeing too much of this in company brochures within the next six months. Ciao! Gordon Moat Alliance Graphique Studio <http://www.allgstudio.com yes, I've experimented with a number of "tea strainer" hole patterns, inspired by some of the commercial softfocus lenses, to try and select a balance of aberrations from various rings to mix with the central hole, varying the number of holes and placement of them and all that (flat black painted discs etc.). Fun project, but by f/8 or so even the single element lenses seem to get "too sharp" to be a truly soft lens anymore ;-) I still have the older versions of Photoshop on my machines at home; the campus machines have the newer stuff, but access is problematic. I'll have to try the aberrations filters, but frankly, these filters and features are getting to be so numerous that you can hardly figure them out before the next version comes out with all new stuff ;-0) Our campus training course for photoshop users is 3 hours on one afternoon, so don't hire any of our graduates without testing them first ;-0) grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > yes, I've experimented with a number of "tea strainer" hole patterns, > inspired by some of the commercial softfocus lenses, to try and select > a balance of aberrations from various rings to mix with the central hole, > varying the number of holes and placement of them and all that (flat black > painted discs etc.). Interesting. I remember either a Schneider or Rollei lens system with strainer aperture disks, but I do not think it is sold anymore. Could be an easy addition. It would seem that a front mounted disk could have the same effect of soft focus. Is there some way to calculate hole sizes, effective aperture, or perhaps just templates? Is TTL exposure required on the camera to ensure proper exposure when using these disks. > Fun project, but by f/8 or so even the single element > lenses seem to get "too sharp" to be a truly soft lens anymore ;-) What confuses me about your statement is why you need f8? Is your lighting gear too strong, and you are not able to open up more than that? To really have an effective soft focus, it would help to have background elements out of focus. If you use f8, it sounds like you are trying to get more in focus, which completely defeats the reason for using soft focus lenses. Bob, your technical discussion is valid, but I am questioning your photography technique. Do you do much wide open aperture photography? Is there a reason you prefer stopping down? > I still have the older versions of Photoshop on my machines at home; the > campus machines have the newer stuff, but access is problematic. I'll have > to try the aberrations filters, but frankly, these filters and features > are getting to be so numerous that you can hardly figure them out before > the next version comes out with all new stuff ;-0) Yes, very true and unfortunate. Adobe needs to keep generating cash flow, so we can expect a new PhotoShop about every year. Even for regular users or PhotoShop (for work), it can take a long time to really effectively use it. The basic strong tools of layers and channels were available since PhotoShop 3, and those are the tools that deserve the most effort. > Our campus training > course for photoshop users is 3 hours on one afternoon, so don't hire any > of our graduates without testing them first ;-0) Typical. Three hours is enough to learn where the tools are, but barely enough to do anything difficult. It was not much different when I graduated in 1998. Consider that the majority of time in PhotoShop under a work situation would involve colour correction for CMYK printing, and creating clipping paths. Many of the tools may seldom be used. I think too many of the filters are strictly for amateur users, since most of the effects degrade image quality. Some newer tool changes can make things go faster, or make newer users aware of editing tools that were previously less intuitive. Anyway, I am curious to hear your opinion of the aberration filter tricks. While I feel it is always better to get the best possible image when taking the original photo, I imagine that many PhotoShop users will want to use this new filter. I hate comments like "fix it in PhotoShop" or "we can PhotoShop that later", since they lessen the importance of good photographic and lighting techniques. Ciao! Gordon Moat Alliance Graphique Studio <http://www.allgstudio.com > Is there some way to calculate hole sizes, effective aperture, or perhaps > just templates? Is TTL exposure required on the camera to ensure proper > exposure when using these disks. It's like a "normal" diaphragm: the ratio of the area covered to the total area. The position, number and shape of the opening(s) is not important. > [...] > Bob, your technical discussion is valid, but I am questioning your > photography technique. Do you do much wide open aperture photography? Is > there a reason you prefer stopping down? I don't know why Bob would prefer stopping down, but let me remark that you mustn't confuse soft focus with shallow depth of field. Varying depth of field will give differently looking images also when softness of focus remains the same. > Yes, very true and unfortunate. Adobe needs to keep generating cash flow, so > we can expect a new PhotoShop about every year. Even for regular users or > PhotoShop (for work), it can take a long time to really effectively use it. > The basic strong tools of layers and channels were available since PhotoShop > 3, and those are the tools that deserve the most effort. "Unfortunate" only for those who feel compelled to buy and install the latest version just because it is that, even when it does not offer anything usefull over the older version already installed. And them the "unfortunate" thing is the compulsion, not the fact that so many new versions appear. > . . . . . . . > > I don't know why Bob would prefer stopping down, but let me remark that you > mustn't confuse soft focus with shallow depth of field. Varying depth of > field will give differently looking images also when softness of focus > remains the same. I have done very little soft focus photography. What little I have done was more wide open. If the opportunity arises for me to do more of this in the future, I will give the greater depth of field with soft focus a try. > > Yes, very true and unfortunate. Adobe needs to keep generating cash flow, > so [quoted text clipped - 8 lines] > latest version just because it is that, even when it does not offer anything > usefull over the older version already installed. I find that many places in California that use PhotoShop for work, stopped at version 5 or 5.5. The learning time of newer versions is one reason, and older established computers is another. There is also a tie between Illustrator, and InDesign, which means upgrading all three . . . more expense. The only work places I know that really keep upgrading constantly are web design businesses. The greatest changes in each version of PhotoShop affect web based imagery more than print intended outputs (not inkjet). > And them the "unfortunate" thing is the compulsion, not the fact that so > many new versions appear. Too much disposable income. It is also interesting that some of the "improvements" just make features that were already there, easier to find and use. While better usability can be nice, the reality is that many users just never knew how to properly use PhotoShop on their prior version. Ciao! Gordon Moat Alliance Graphique Studio <http://www.allgstudio.com > > yes, I've experimented with a number of "tea strainer" hole patterns, > > inspired by some of the commercial softfocus lenses, to try and select [quoted text clipped - 6 lines] > easy addition. It would seem that a front mounted disk could have the same > effect of soft focus. The lens you refer to is the Rodenstock "Imagon". It was available for the Rollei SL66 camera, among others. It should come with an ND filter and a few different aperture disks, if you find a used one. ;-) Lourens > > > yes, I've experimented with a number of "tea strainer" hole patterns, > > > inspired by some of the commercial softfocus lenses, to try and select [quoted text clipped - 12 lines] > ;-) > Lourens Thanks Lourens. I only remembered seeing it in reference to Rollei, though I have never seen one in use. Ciao! Gordon Moat Alliance Graphique Studio <http://www.allgstudio.com > > > > yes, I've experimented with a number of "tea strainer" hole patterns, > > > > inspired by some of the commercial softfocus lenses, to try and select [quoted text clipped - 20 lines] > have > never seen one in use. an Imagon also exists for Mamiya RB, if I'm correct. (and also for 4x5" of course) The few times I have used soft focus I have applied it in the darkroom btw, which gives a negative effect with the black going slightly into the light areas. It's also easier to maintain contrast. Looks nicer i.m.o.... I don't like high-key very much. ;-) Lourens > snip > > Interesting. I remember either a Schneider or Rollei lens system with > strainer aperture disks, but I do not think it is sold anymore. Could be an > easy addition. It would seem that a front mounted disk could have the same > effect of soft focus. Rodenstock Imagon > snip > [quoted text clipped - 5 lines] > more in focus, which completely defeats the reason for using soft focus > lenses. Try a Busch Nicola Perscheid objektiv. > huge snip Cheers, Dan Dan Fromm wrote:. . . . . . > > To really have an effective soft focus, it would help to have background > > elements out of focus. If you use f8, it sounds like you are trying to get > > more in focus, which completely defeats the reason for using soft focus > > lenses. > > Try a Busch Nicola Perscheid objektiv. Now you got me going another direction . . . will need to investigate that one. Ciao! Gordon Moat Alliance Graphique Studio <http://www.allgstudio.com yes, the usual aperture priority or TTL metering (stopped down etc.) should work fine, as it is measuring total light etc. yes, you can put these cutouts in front of the lens; I have a gizmo called a pictrol which screws onto the lens front with 3 screws, as you turn it, a series of white plastic wedges extend from half-dozen directions towards the center of the lens. this front of the lens adapter gives a variety of softening effects, unlike a simple filter, which can be dialed to suit the subject (e.g., more wrinkles, more softening ;-) most soft focus lenses (as opposed to filters) work by having a large degree of uncorrected spherical aberration, esp. in the outer margins (rings) of the lens. The sieve designs let you mix light from this zone with the smaller central zone (f/8-ish in my experience) to produce the degree of softening you want. The central zone alone produces a relatively sharp image, the outer rings smear light about in a softening and hopefully pleasant manner, and the combo produces a sharp central image with a bit of blur. Most softening filters simply produce a blur, without a variable degree of central sharpness image effect. So you get a different image with these lenses than with the low cost softening filters or mesh stocking tricks etc.... re: f/8 What I would like is a poor man's defocus control lens, using older optics with considerable uncorrected spherical aberration to provide an attractive bokeh by mixing this "3-d" light from the periphery with the sharp central image. With a defocus control lens, you can vary the amount of spherical aberration (and type, for front or back of plane of focus effects), and still control the bokeh at relatively small f/stops due to the lens design. Unfortunately, if you need to do this to get good DOF with nice bokeh in a subject with a soft focus lens, you can't, because the small opening needed at f/5.6-f/16 range is too small to let you mix in much light from the outer ring and still be at f/11 or f/8. So you are limited to getting nice bokeh only with soft lens effects wide open. It would be nice to get nice bokeh at all stops, or be able to vary the bokeh effects at various stops, as with a defocus control lens, simply by switching out sieve patterns. I wish I had more time to get into PS, and a better facility on campus to do so, but I have over a hundred computer books now. Most of them don't have much plot or character development, and the dialogue is boring too;-) The photoshop books and "bibles" tend to be even longer than usual = aargh! ;-) grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > re: f/8 What I would like is a poor man's defocus control lens, using > older optics with considerable uncorrected spherical aberration to provide > an attractive bokeh by mixing this "3-d" light from the periphery with the > sharp central image. Didn't Spiratone have an inexpensive lens that they sold for just that purpose? My memory is fuzzy on this, but I seem to recall that it might have been made of brass, and did not have an adjustable aperture--it was meant to be shot wide open and it had what was describes as a pleasing soft-focus effect. They advertised it in the photo mags almost every month, for years. yes, the old spiratone corp (of fred spira fame) had a lot of oddball and nifty items, often cheap (in both senses of the term ;-) which included some soft focus lenses. like the sima variant, these were generally +10 diopter lenses or similar (100mm equiv, usually 50mm so f/2-ish wide open) with a lot of spherical aberration, as you noted; T-mount IIRC? you can simply put a +10 diopter lens on a bellows and start experimenting too ;-) these soft focus optics can be fun lenses to make, and I suspect that many would cover 6x4.5cm and maybe 6x6cm too, similar to the plungercam loupe lens setup for hasselblad ;-) see http://www.marktucker.com one of the nice things about these optics is that they give the kind of results that "only a bad lens can give" - soft focus, ethereal, lots of flare, faults long since banished from today's optimized optics ;-) yes, there are a few soft focus lenses out there, but often not in all MF lines, and they are pretty costly, largely due to limited sales volume an not original cost ;-) so being able to adapt some bad lenses to a good body via bellows may be a fun project, and excuse to buy some very low cost dog lenses to try out for their bokeh ;-) don't forget to unscrew the lenses and try each lens half etc. for effects, often half a lens is better than a whole one too ;-) grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > yes, the old spiratone corp (of fred spira fame) had a lot of oddball and > nifty items, often cheap (in both senses of the term ;-) which included [quoted text clipped - 19 lines] > don't forget to unscrew the lenses and try each lens half etc. for > effects, often half a lens is better than a whole one too ;-) I once saw a very creative eBay seller trying to pass of a Takumar lens that had fungus growing on one of the inner elements. He just called it a "soft focus portrait lens!" There is another auction up right now for a Spotmatic camera in black enamel that shows a considerable amount of brassing. The descriptive copy reads, "I believe that this camera is made of brass . . ." Very creative way to hype junk! I DID buy a Spiralite diffuser filter, back in the 70s. It was apparently a plain glass filter, on which was sprayed some water-soluble substance (maybe hairspray?). I was foolish enough to clean it with Kodak lens cleaner fluid, and it dissolved the sprayed-on substance, leaving only the plain glass surface remaining. That was the end of my diffusion filter! sorry about the lost filter, but you can use the same trick to make your own, including various spot clear center soft filters, see tips at http://medfmt.8k.com/bronfilters.html#homebrew Other tricks include black mesh stockings as diffusers etc. Unfortunately, the results of such diffusers is an overall softening effect, and if you want a sharp main image with softening overlay, you have to go for either the zeiss softars (acting like a sequence of small lenses, sort-of ;-) or a true soft focus lens (as with the imagon cited in the thread above ;-). Since many of these soft focus lenses cost a good bit more than the average sharp focus lens on the same mounts, and aren't available on many popular mounts (e.g., I don't have a SL66 - yet ;-), it forces many of us to look for a work-around using less costly optical tricks with simple and low cost optics. Plus it is more fun and you can develop a range of tricks with various "bad" lenses ;-) grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* I miss old Fred... Denny - formerly poor and a customer of Fred... > yes, the old spiratone corp (of fred spira fame) had a lot of oddball and yes, me too ;-) I am surprised that there hasn't been someone taking up those odd-ball items, other than perhaps porters camera and freestyle sales corp., esp. since the new mounts and digital cameras offer a lot of opportunity for some creative marketing and sales ;-) And lots of low cost items would be very low cost nowadays, given chinese photo mfgering and the relative simplicity of many of the items spiratone sold. I have a number of catalog and ad pages from the 1960s and 1970s, and it is a bit amazing to see how many strange items managed to find a market among photographers ;-) I am still looking for a replacement 220 degree fisheye (a silvered hemisphere with +20 diopter lens and clear plastic tube so you could take photos covering 220 degrees, including the camera!) and another 7.5mm fisheye Tmount from spiratone/sigma ;-) grins bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* > yes, the usual aperture priority or TTL metering (stopped down etc.) > should work fine, as it is measuring total light etc. [quoted text clipped - 5 lines] > softening effects, unlike a simple filter, which can be dialed to suit the > subject (e.g., more wrinkles, more softening ;-) Any example images? Since I am exploring surrealism lately, perhaps I can work this into some images. > most soft focus lenses (as opposed to filters) work by having a large > degree of uncorrected spherical aberration, esp. in the outer margins [quoted text clipped - 7 lines] > different image with these lenses than with the low cost softening > filters or mesh stocking tricks etc.... You know, this brings it back to your search for cheap lenses. Using a telephoto, and a low power, and low cost, diopter on the front of the lens, there is a slight softening of the corners. While this is only good to use at close distances, and more for head shots, the effect can be flattering. > re: f/8 What I would like is a poor man's defocus control lens, using > older optics with considerable uncorrected spherical aberration to provide [quoted text clipped - 5 lines] > still control the bokeh at relatively small f/stops due to the lens > design. I checked out the Nikon 105 mm defocus lens for 35 mm SLRs. I find it disappointing, mostly due to the price, but also because the regular 105 mm f2.5 gives such great defocus anyway. The other issue is that the more controls on a lens, the more you slow down. Too much fiddling, and your subject/client/art director could get bored or frustrated with you. Older gear is the poor man's journey into great lenses. There is a wealth of great choices for the budget conscious photographer, though obviously with some reservations in usage. > Unfortunately, if you need to do this to get good DOF with nice bokeh in a > subject with a soft focus lens, you can't, because the small opening [quoted text clipped - 4 lines] > stops, as with a defocus control lens, simply by switching out sieve > patterns. I don't have a problem shooting wide open. When there is too much light, adding an ND works quite well, and is easy to do. > I wish I had more time to get into PS, and a better facility on campus > to do so, but I have over a hundred computer books now. Most of them don't > have much plot or character development, and the dialogue is boring too;-) > The photoshop books and "bibles" tend to be even longer than usual = > aargh! ;-) Yeah . . . typical problem with software books. There are too many on PhotoShop. It is better to simplify, and get a smaller book. These often get one up to speed much faster, and have a lower frustration level. You might have this one, but stick to the Visual QuickStart Guide to PhotoShop. This is a Peach Pit Press publication, very small, but very effective and easy to use. Take the rest, and donate them to a library. Ciao! Gordon Moat Alliance Graphique Studio <http://www.allgstudio.com ah, interesting tip, yes, thanks very much, I'll have to give the diopter plus telephoto lens a try. I recall a formula on my diopters pages for such combos (as well as negative lenses in front of the lens too IIRC) at http://medfmt.8k.com/mf/diopter.html to work out the effect on focal length etc. ;-) But I hadn't thought to try it with large + diopters; I usually only use a fractional diopter lens (+1/2..) to get closer focusing with my bronica nikkor 200mm etc. I also use the crappy +1.5X plastic/glass telephoto converters on the normal lens of fixed lens kits to get a softened telephoto effect, not sharp (even at f/8 ;-) but my bet is this is a similar optical setup to what you are doing with the front of the lens diopter tricks too? ;-) I also list my nikkor 105mm f/2.5 lenses as among the best bokeh in the nikon line (as do many of us ;-), esp. at the low prices these cost ;-) I think you are right that a major part of the fun of looking for good bokeh lenses is finding truly "bad" older lenses which can provide a unique look. One major benefit is that dealers are all to anxious to get rid of these doggie lenses for minimal $$, the big problem is they have given up on selling them and so leave them in boxes in shop instead of dragging them to our local camera shows ;-) the surrealism project sounds like fun ;-) the listing of some softening filter tricks can be found at http://medfmt.8k.com/bronfiltersp.html#homebrew and in related postings; one trick with the vaseline from the late 1960s is to put in food dye colors in the vaseline, then smear them around. Verrry surreal ;-) leave a clear spot and shoot the bride in the middle clear spot with swirling colors around her ;-) we could probably generate a lot of ideas on surreal soft filtering effects and tricks here, I've learned a few already - thanks! ;-) regards bobm Signature*********************************************************************** * Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 * ********************Standard Disclaimers Apply************************* "Soft focus" lenses are not just lenses with crummy resolution and no coating, nor a lens simply shot wide open or slighly defocused. And some add-on softeners do not really do the same thing the old intentionally soft lenses did, however a lot of people are happy with the Zeiss Softars (three grades of them), but in that case you start out with a spendy lens, add a spendy filter to get a lousy lens. Half-kidding, really. The Softar filters are rather sophisticated with a hundred or so tiny, shallow lenses, or refractors, whatever. I have three soft-focus lenses for LF and in each case the degree of soft-focus can be dialed in after focusing and stopping down. For production work, you just use preset combinations determined by experimentation. It's hard to see soft-focus with a stopped-down lens. > > sure, see http://medfmt.8k.com/mf/hassylenses.html - zeiss has an APO lens > > series for hasselblad for example, [...] [quoted text clipped - 18 lines] > > Zeiss has a series of superachromats for Hasselblad. But no (!) apochromats. In the optics industry, refractive lenses having 4 or 5 zero crossings in the longitudinal color curve are sometimes referred to as superachromats, but these are very uncommon and require very tight glass tolerances to actually build as designed. I've also heard the term applied to certain UV-VIS-IR hyperspectral apochromats. Of course, its clearly impossible to bring *all* wavelengths to a common focus in any optical system containing powered refractive elements. I would be careful of using a "to all intents and purposes" type of definition. After all, simple scaling can transform any lens into a superachromat if that kind of definition is used. Brian www.caldwellphotographic.com > [...] Of > course, its clearly impossible to bring *all* wavelengths to a common > focus in any optical system containing powered refractive elements. I > would be careful of using a "to all intents and purposes" type of > definition. After all, simple scaling can transform any lens into a > superachromat if that kind of definition is used. The "all" bit in "to all intents and purposes" may be misleading since it validity is confined to the photographic context, excluding exotic parts of the spectrum. But there it is valid: it is indeed possible (as shown by Zeiss) to bring all wavelengths used in photography to a common focus, i.e. such that the deviations still present are causing less harm to image formation and resolution than other faults, and diffraction, would cause. That includes wavelengths that are not normally used in photography, like the near IR (the Sonnar-Superachromat 250 mm has the same focal length for near IR and for "visible"/actinic light) or UV (the UV-Sonnar, a superachromat in all but name, has the same focal length for UV and "visible" light.), or UV, visible, and IR (the Asahi Ultra-Achromatic Takumar 85 mm lens has a common focal length for all wavelengths between 220 and 1000 nm). > Of course, its clearly impossible to bring *all* wavelengths > to a common focus in any optical system containing powered > refractive elements. Why? All you need is the right glasses, and you can smoothly correct for an entire spectrum. SignatureTranspose hotmail and mxsmanic in my e-mail address to reach me directly. > > Of course, its clearly impossible to bring *all* wavelengths > > to a common focus in any optical system containing powered > > refractive elements. > > Why? All you need is the right glasses, and you can smoothly correct > for an entire spectrum. Thats right. All you need are the right glasses. But they don't (quite) exist. And even if the perfect glass types could be produced a mathematically perfect correction would be lost by an infinitisimal change in temperature. In practice you can do a more than adequate job in most cases, and secondary/tertiary spectrum can be reduced to negligible levels. Brian www.caldwellphotographic.com > All you need are the right glasses. But they don't > (quite) exist. How does Zeiss do it? SignatureTranspose hotmail and mxsmanic in my e-mail address to reach me directly. > > All you need are the right glasses. But they don't > > (quite) exist. > > How does Zeiss do it? They don't. > > How does Zeiss do it? > > They don't. Not over a spectrum ranging from gamma rays to micro waves, but they do. > > > How does Zeiss do it? > > > > They don't. > > Not over a spectrum ranging from gamma rays to micro waves, but they do. 4 or 5 crossings in the visible spectrum (or perhaps slightly extended visible spectrum) are possible with available materials, but absolute perfect chromatic correction over a non-trivial spectral band can only be achieved with catoptric designs. *Every* refractive or catadioptric optical system ever made has had residual chromatic errors. Zeiss is good solid optical company, but is subject to the same limitations that apply to everyone else. Brian www.caldwellphotographic.com > > Not over a spectrum ranging from gamma rays to micro waves, but they do. > [quoted text clipped - 5 lines] > errors. Zeiss is good solid optical company, but is subject to the > same limitations that apply to everyone else. Of course there are residual errors. The question is how big this residual error still is. That's where the difference between a good optical designer and a mere competent one shows. The first Zeiss superachromat, the 1972 Sonnar-Superachromat 250 mm lens (all refractor) has a secondary spectrum so far reduced that its influence on the image is well below the rayleigh limit, i.e. to all intent and purpose it did not exist. That correction is the same over the entire range from approx. 400 nm to 1000 nm. A non-trivial spectral band indeed. Later Zeiss Superachromats are the same, though they differ from the 250 mm in that they don't hold the same superb correction into the short IR band. That, by the way, is a matter of fact. Not a theoretical consideration. Feel free not to believe that. These lenses are still available today. So just get one, and run your tests... > ... into the short IR band. Short IR = red SignatureTranspose hotmail and mxsmanic in my e-mail address to reach me directly. > > ... into the short IR band. > > Short IR = red No, no, no. Short IR is a part of the IR spectrum. That's why it's called short *IR*... The IR band ranges from wavelengths as short as 750 nm to long wavelength of 1 mm (yes, millimeter, not nanometer). Only the part comprising the short wavelenghts ranging from 750 nm to about 1000 nm can be captured photographically: "short IR". (In fact, "short IR" also includes the second "IR octave", ranging from 1500 to 3000 nm, but that part evades photographic capture (there are other ways of registering this, and longer bands of IR), so it is ignored in a photographic context ;-)). > > > Not over a spectrum ranging from gamma rays to micro waves, but they do. > > [quoted text clipped - 25 lines] > Feel free not to believe that. These lenses are still available today. So > just get one, and run your tests... Keeping residual aberrations below the Rayleigh limit is certainly an adequate practical description of optical perfection. However, this would be difficult to achieve for a lens as short as 250mm covering a large 6x6cm format. It would certainly be wasted on ordinary films and non-vacuum film backs. Is there documentation online showing that this level of correction has actually been achieved? > Keeping residual aberrations below the Rayleigh limit is certainly an > adequate practical description of optical perfection. However, this > would be difficult to achieve for a lens as short as 250mm covering a > large 6x6cm format. It would certainly be wasted on ordinary films > and non-vacuum film backs. Is there documentation online showing that > this level of correction has actually been achieved? You may want to go to the horse's mouth and look at what Zeiss has to say: http://www.zeiss.de > You may want to go to the horse's mouth and look at what Zeiss has to say: > http://www.zeiss.de The horse says "The so-called secondary spectrum, the dominating lens aberration in telephoto lenses, is so well corrected over the entire spectral range from 400 nanometers (the border of the ultraviolet range) to 1,000 nanometers (which is far inside the infrared domain), that residual aberrations are within the Rayleigh limit of focussing uncertainty." The lens is diffraction-limited in the center area of the field, also. SignatureTranspose hotmail and mxsmanic in my e-mail address to reach me directly. > > Keeping residual aberrations below the Rayleigh limit is certainly an > > adequate practical description of optical perfection. However, this [quoted text clipped - 5 lines] > You may want to go to the horse's mouth and look at what Zeiss has to say: > http://www.zeiss.de Q: I have no doubt that this is an excellent lens which is probably overkill on a 6x6 SLR film body. The website mentions that the longitudinal chromatic errors between 400nm and 1000nm are kept below the Rayeigh limit for defocus. I'm willing to believe this because I've designed systems over this same waveband with similar focal length which are also within the Rayleigh limit at f/5.6. Note that these systems were technically apochromats, with three crossings in the 400-1000nm band. Like I said before, Zeiss is subject to the same limitations we all face. Interestingly, the webpage also states that the lens is diffraction-limited near the center of the image, but the MTF curves indicate that performance improves slightly as you stop down to f/8. The MTF curves clearly show that anything approaching diffraction-limited performance at f/5.6 is completely lost once you move a modest distance off-axis. Brian www.caldwellphotographic.com > Note that these systems were technically apochromats, with > three crossings in the 400-1000nm band. Like I said before, > Zeiss is subject to the same limitations we all face. And they have the same possibilities. With the right glass, and with the other precautions they take, I don't see why they cannot effect continuous correction throughout a frequency band. You may not have managed that in the systems you designed, but it sounds like Zeiss has. > The MTF curves clearly show that anything approaching > diffraction-limited performance at f/5.6 is completely lost once you > move a modest distance off-axis. So? The documentation does not claim otherwise. SignatureTranspose hotmail and mxsmanic in my e-mail address to reach me directly. > > Note that these systems were technically apochromats, with > > three crossings in the 400-1000nm band. Like I said before, [quoted text clipped - 4 lines] > continuous correction throughout a frequency band. You may not have > managed that in the systems you designed, but it sounds like Zeiss has. The point I was making, which you have missed, was that the correction in both cases is about the same. The Zeiss lens *does not* have continuous perfect correction through the stated waveband; rather the residual axial color errors fall within the Rayleigh limit for defocus. Brian www.caldwellphotographic.com > The Zeiss lens *does not* have continuous perfect correction > through the stated waveband; rather the residual axial color > errors fall within the Rayleigh limit for defocus. How do you know? SignatureTranspose hotmail and mxsmanic in my e-mail address to reach me directly. > Q: > I have no doubt that this is an excellent lens which is probably [quoted text clipped - 6 lines] > the 400-1000nm band. Like I said before, Zeiss is subject to the same > limitations we all face. Stop protesting! The Zeiss ones *are* Superachromats. ;-) Max Herzberger (with or without Nancy McClure) started these things some 40 years ago, showed how to do this. Herzberger and McClure (both working for Eastman Kodak) designed one in the early 1960s that was achromatized for the F, D, C and g-lines (4 wavelenghts indeed, so technically not (!) an apochromat.). I can't find the particulars of the Zeiss Sonnar-Superachromat, but the fourth line it is achromatized for must be somewhere in the near IR part of the spectrum. Zeiss (and Herzberger, and McClure and Arthur Cox, and the designers at Pentax, and who knows else achieved the same) indeed all are subject to the same limitations we all face. But what was that again i said before about good designers and mere competent ones...? ;-) But again, it is not the number of wavelengths it is achromatized for, and whether technically it is a apochromat (which it is not) or a superachromat (which it is), it is what happened to the secondary spectrum. > Interestingly, the webpage also states that the lens is > diffraction-limited near the center of the image, but the MTF curves > indicate that performance improves slightly as you stop down to f/8. > The MTF curves clearly show that anything approaching > diffraction-limited performance at f/5.6 is completely lost once you > move a modest distance off-axis. Shows how concentrating on eliminating one aberration does not automatically produce perfect lenses, doesn't it? ;-) > > Q: > > I have no doubt that this is an excellent lens which is probably [quoted text clipped - 8 lines] > > Stop protesting! The Zeiss ones *are* Superachromats. ;-) No protest, just pointing out that similar correction can be achieved with plain old apochromats having only three crossings. I would like to see Zeiss publish an actual longitudinal color curve for the design, however. There is a Zeiss patent covering designs that appear similar to the 250/5.6 (U.S. Patent 3,883,230), and superachromat design ala Herzberger is discussed in the text. However, the examples I've looked at in detail only have ordinary apochromatic performance. Part of this might be due to small errors in glass specification and/or round off errors in the examples. > Max Herzberger (with or without Nancy McClure) started these things some 40 > years ago, showed how to do this. Herzberger and McClure (both working for [quoted text clipped - 9 lines] > same limitations we all face. But what was that again i said before about > good designers and mere competent ones...? ;-) Wasn't it Herzberger who created the phrase "superachromat" back in the mid-1960's with reference four chromatic crossing system you mentioned above? > But again, it is not the number of wavelengths it is achromatized for, and > whether technically it is a apochromat (which it is not) or a superachromat > (which it is), it is what happened to the secondary spectrum. Agreed. Number of wavelength crossings is almost an academic thing which may not be directly related to actual performance. Its also true that even if you design a system with 4 color crossings you may not actually get that many in an as-built system due to tolerance problems. > > Interestingly, the webpage also states that the lens is > > diffraction-limited near the center of the image, but the MTF curves [quoted text clipped - 5 lines] > Shows how concentrating on eliminating one aberration does not automatically > produce perfect lenses, doesn't it? ;-) Certainly true, although it is usually helpful to know *how* to eliminate a particular isolated aberration in order to gain the intuition necessary to bring about better overall correction. Brian www.caldwellphotographic.com > No protest, just pointing out that similar correction can be achieved > with plain old apochromats having only three crossings. Ah yes. Indeed. But before Bob jumps up and shouts "see!", let me remind him that there is a difference between "can be" and "is", and that the point of Zeiss' SA lenses is that very "is". ;-) > I would like > to see Zeiss publish an actual longitudinal color curve for the [quoted text clipped - 4 lines] > Part of this might be due to small errors in glass specification > and/or round off errors in the examples. It's always good to see actual, measured data, yes. Anyway, yes, the Determann/Zajadatz patent looks like it covers the 250 mm lens. Example 2 in the U.S. patent appears to be the one. Now i think i understand too what it is that Zeiss thought needed additional patenting. Though texts like "Zeiss found a way to even improve on apochromatic performance: the superachromatic correction" (example taken from Camera Lens News, No. 8) are a bit presumptuous. Thanks for the reference cited! The only way i have actually had an opportunity to "test" the 250 mm Sonnar-Superachromat is by using one in a normal photographic situation (the lens was borrowed, not my own. Alas...), and i can say that it really makes a difference: it is a very sharp lens indeed. I would be happy owning one even if it only has three crossovers. Zeiss, however, do indeed claim that their three superachromats have four crossovers. ;-) > Wasn't it Herzberger who created the phrase "superachromat" back in > the mid-1960's with reference four chromatic crossing system you > mentioned above? Yes. My earlier "And yes, it's a Zeiss invented term (and thing) too" was rather inaccurate... ;-) The idea of correcting for yet another wavelength obviously is something that evades claims of invention, but Herzberger was the first to describe a way to actually do it. What Zeiss did was register the name "superachromat" as trademark (how that is possible escapes me. But then, a patent was applied for, and actually awarded, covering the thing we call "life". So anything goes, it seems). And produce an actual, "useful", lens that meets the promised level of correction. Their interpretation of Herzberger's work, and with it the term "superachromacy", is a complete removal of the secondary spectrum. Deviating a bit from the "original" meaning perhaps, yet stressing what is important. Apropos built tolerances: of course more attention must be given, all throughout the manufacturing proces of these lenses. Tolerances must be tight enough, and must be kept. But that's not impossible, is it? ;-) If you do not know it already, you might enjoy reading the "story" of how the Zeiss Tele Superachromat f/2.8 300 mm was produced. I believe it is "up" somewhere on the Zeiss website, or else on the Hasselblad website (http://www.hasseblad.se). This lens, by the way, also is corrected into the IR band. > Certainly true, although it is usually helpful to know *how* to > eliminate a particular isolated aberration in order to gain the > intuition necessary to bring about better overall correction. Yes, of course. But the impression (which my ravings about the Zeiss SA may create ;-)) must be avoided that these lenses are perfect. |
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