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Photo Forum / Digital Photography / DSLR Cameras / February 2007Are IS lenses doomed ?
The release of Sony Alpha with the image stabilization in camera ( although this is not new) highlighted the fundamental problem with Canon. Canon have had IS lenses long ago as it would be very difficult to do in-camera stabilization in film cameras. The digital cameras had to support older lenses including the ones with IS. If Canon developed a camera with in-body stabilization it would hurt Canon sales and reputation. So I guess Canon will continue with its nonstabilized bodies and when Sony or someone else will achieve the same image sensor quality Canon will find itself in a very difficult situation. There is a very small advantage in having IS in the lens but it is not significant enough to grant double and triple cost of the same quality lenses. What do you guys think ? > The release of Sony Alpha with the image stabilization in camera ( > although this is not new) highlighted the fundamental problem with [quoted text clipped - 11 lines] > lenses. > What do you guys think ? Until someone comes up with a sensor-based IS that is as effective as Canon and Nikon IS/VR at all focal lengths, they have nothing to worry about save for Sony's less-than-honest marketing tactics.  SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson > Until someone comes up with a sensor-based IS that is as effective as > Canon and Nikon IS/VR at all focal lengths, they have nothing to worry > about save for Sony's less-than-honest marketing tactics. Isn't that the truth? A lot of people are uninformed enough to believe IS is going to help freeze sports action, as shown in Sony's marketing campaign. >The release of Sony Alpha with the image stabilization in camera ( although >this is not new) highlighted the fundamental problem with Canon. >Canon have had IS lenses long ago as it would be very difficult to do >in-camera stabilization in film cameras. The digital cameras had to support >older lenses including the ones with IS. If Canon developed a camera with >in-body stabilization it would hurt Canon sales and reputation. How on earth would in-camera IS hurt Canon's reputation? Sales, maybe, because in-camera IS would /eventually/ kill off their market for IS lenses, but a huge number of photographers (including myself) would consider in-camera IS on Canon DSLRs to be a godsend, & would be saving their pennies to buy one ASAP. > because in-camera IS would /eventually/ kill off their market for IS > lenses, but a huge number of photographers (including myself) would > consider in-camera IS on Canon DSLRs to be a godsend, & would be > saving their pennies to buy one ASAP. There might even be a little to be gained by using an IS lens on an IS chip. Probably not much, but possibly something. Also, I'm thinking IS in a 300+ mm lens is going to do a lot better than on a chip. >> because in-camera IS would /eventually/ kill off their market for IS >> lenses, but a huge number of photographers (including myself) would [quoted text clipped - 3 lines] >There might even be a little to be gained by using an IS lens on an IS >chip. Probably not much, but possibly something. Dunno. It'd be awfully hard to prevent the two IS mechanisms from confusing each other. If Canon do ever introduce an in-camera IS system, I'd bet that they configure the camera firmaware to turn off the body IS when an IS lens is mounted. >Also, I'm thinking IS in a 300+ mm lens is going to do a lot better >than on a chip. On that, I agree with you. In-camera IS would need a huge amount of travel to compensate for the amount of shake you get with big tele lenses. >>Also, I'm thinking IS in a 300+ mm lens is going to do a lot better >>than on a chip. > > On that, I agree with you. In-camera IS would need a huge amount of > travel to compensate for the amount of shake you get with big tele > lenses. What actually happens with in-body IS is that the travel is the same in extent, it's just the velocity (speed of travel) which increases with longer focal lengths. Sony (Minolta) use angular momentum sensors, since it is an angular shake which counts, so shake is not considered in mms it's in degrees (or small fractions of a degree) plus velocity. When a lens covers 8 degrees a quarter degree of shake is substantial, when a lens covers 80 degrees it's not so much. However, you are 'safe' to shoot at 1/30th without IS on an 18mm lens, but you have to use 1/500th to be safe on a 300mm lens (both APS-C examples). The long lens magnifies the shake in effect, so that the image moves as far in 1/500th with the 300mm, as it moves in 1/30th with the 18mm. The long lens only gets into 'huge amount of travel' if you try to hand-hold 1/30th at 300mm. With anti-shake, you can do 1/8th and maybe 1/4 at 18mm. You can do 1/250 or 1/125 at 300mm. In each case, the sensor is travelling about the same amount, but it is having travel faster for the 300mm. Shake does not just keep going in one direction, anway. It tends to be tremor or vibration-like when it is not a brief, fixed jerk caused by pressing the shutter. Sony's SSS will cope with tremors between 1Hz (swaying gently back and forth once a second - heartbeat, breathing) and 60Hz (someone just plugged you into a wall socket by mistake). Most shake is apparently around 10Hz, a typical frequency of human body tremor. So the system, whether in the lens or the body, has to respond to acceleration, fixed velocity, vector (direction) including rapid changes of all three. Both in-lens and in-body IS appears to function equally well over a wide range of conditions. It's not possible to state that in-lens IS is definitely superior at long focal lengths, on in-body superior with extreme wides and hand-held 1/4s. In practice I have found my KM and Sony bodies very similar to Canon IS with 100-300mmm/70-300mm lenses (the KM 100-300mm is much smaller and lighter than our early Canon IS 70-300mm, but I don't think this improves the efficiency - if anything the large Canon lens is a bit easier to hand-hold steadily). What I forget - and I suspect many others forget - is that you really should not be able to use 1/30th with either system, if the lens is at 300mm. I do so regularly, and the result is nearly always perfectly sharp. That's 4-5 stops of stabilisation, not the claimed 1-2 for the older Canon lens, or 2-3 for the KM/Sony systems. Yet both, with a little care, will give a high success rate. David >>> Also, I'm thinking IS in a 300+ mm lens is going to do a lot better >>> than on a chip. [quoted text clipped - 16 lines] > image moves as far in 1/500th with the 300mm, as it moves in 1/30th with > the 18mm. No, you haven't worked out your math. Your 1/500 on 300 mm is above the 1/fl guide, so IS is not needed. Newest IS on canon claims 4 stops, so if 1/300 is the guide, then 4 stops is 1/20 second. At 18mm, the guide is 1/20 second, and 4 stops is 1 second. The IS feedback loops don't work well at 1 second. Image shake of ~1 arc-minute per 1/20 second, and tracking needs to be at least ~10 times that level (you can't keep your shake to 1 arc-minute pointing accuracy). Thus a range of 10 arc-minutes is needed at a rate of 20 arc-minutes/second. For a 300 mm lens that works out to a range of 0.9 mm (900 microns), and a rate of 1800 microns/second, with a required accuracy of ~ 2 microns (pretty difficult. Now try that with a 600 mm lens, then a 600 mm + 2x TC. Rate goes up in proportion to focal length, but so does the range, because you can't accurately point to the 1-arc-minute limit, you need a larger limit, and that is at best constant and in reality worsens as you hold more weight. Thus 1200mm would require 3.6 mm range at a rate of 7200 microns/sec with an accuracy of ~2 microns. It can be done in a lens because you can tune the power of the optical element being moved to give image movement within the range and accuracy of the device doing the movement. Also, in my experience, the 1/fl guide falls apart as the lens size goes up, and the longer you hold the lens. Try holding an 8-pound 500 mm f/4 lens for a while. Thus, for telephoto work, in lens IS is the only reasonable engineering solution. Here are example of high magnification hand help in lens IS: For this image, a friend was shooting with a 300 f/2.8 non IS lens and got no good images, despite using faster shutter speeds and lower magnification. My image was 1/1600 sec at 500 mm: http://www.clarkvision.com/galleries/gallery.bird/web/road.runner.c11.29.2005.JZ 3F5598.b-700.html This one even with IS, about half the images I took were sharp, the other slightly blurry: http://www.clarkvision.com/galleries/gallery.bird/web/c12.18.2002.IMG_2794.hawk. b-600..html Roger > The long lens only gets into 'huge amount of travel' if you try to > hand-hold 1/30th at 300mm. With anti-shake, you can do 1/8th and maybe [quoted text clipped - 29 lines] > > David >>>Also, I'm thinking IS in a 300+ mm lens is going to do a lot better >>>than on a chip. [quoted text clipped - 9 lines] >When a lens covers 8 degrees a quarter degree of shake is substantial, >when a lens covers 80 degrees it's not so much. I think I must have missed some vital point here, David. How does an angular movement of the camera, which moves the image in linear fashion along the sensor, require a change in the angular orientation of the sensor. ISTM that it must require a linear movement of the sensor to correct it. OTOH, it is quite feasible to change the location of an image on the sensor by a small angular displacement of the image-forming beam somewhere in the lens, and quite credible that this would require much smaller movements. If I have misunderstood this (and many others have too, including Canon, who I see give a similar rationale for favouring lens-based IS), is there a suitable web site which explains the position? I freely acknowledge a lack of specific expertise here, and accept the situation may be more complicated than my simple thoughts here. >However, you are 'safe' to shoot at 1/30th without IS on an 18mm lens, >but you have to use 1/500th to be safe on a 300mm lens (both APS-C [quoted text clipped - 33 lines] >older Canon lens, or 2-3 for the KM/Sony systems. Yet both, with a >little care, will give a high success rate. I guess this is the ultimate test - if in-camera works as well as in-lens, then it is as good. Would be good to see some rigorous tests though. David SignatureDavid Littlewood >>>> Also, I'm thinking IS in a 300+ mm lens is going to do a lot better >>>> than on a chip. [quoted text clipped - 16 lines] > sensor. ISTM that it must require a linear movement of the sensor to > correct it. I didn't mean the sensor changes angle in any way - it correct while remaining strictly plane-parallel in its film plane. The calculation as to how much linear movement to give is based on research into camera shake, which shows that linear movement of the entire camera is rare and causes very little visible shake; angular (so-called rotational) shake is universally the main cause of unsharpness, but it has to be corrected by a linear movement of the sensor corresponding to the image movement. This subject has been discussed to death on the Sony forum on dPreview as a result of a misinformed ideas by a physics graduate (it's very easy to get it wrong if you think camera shake is a displacement of the lens axis, rather than a dip/swing/tilt of the lens axis). My conclusion, after some very useful posts from others including one which emphasised that long lenses don't need greater sensor movemen if you stick to the rules about shutter speeds (with the IS factor included), was that the programming is pretty complex and relies on 'typical' shake detection. There is no way the sensors in the Sony can really tell whether displacement, rotation, etc is causing them to detect motion. Somewhere in the system (same goes for IS in lens) the designers have said 'if the signal from the sensors is THIS, the required correction will be amost certainy be THIS'. It is not actually a direct link. David >> I think I must have missed some vital point here, David. How does >>an angular movement of the camera, which moves the image in linear [quoted text clipped - 10 lines] >corrected by a linear movement of the sensor corresponding to the image >movement. Thanks; I think misunderstood your previous post. The above matches my understanding; clearly you are right that linear displacement will cause a very small effect compared with angular changes. >This subject has been discussed to death on the Sony forum on dPreview >as a result of a misinformed ideas by a physics graduate (it's very >easy to get it wrong if you think camera shake is a displacement of the >lens axis, rather than a dip/swing/tilt of the lens axis). Not a forum I follow, but thanks. >My conclusion, after some very useful posts from others including one >which emphasised that long lenses don't need greater sensor movemen if [quoted text clipped - 6 lines] >required correction will be amost certainy be THIS'. It is not actually >a direct link. I can imagine this would be a reasonable approximation, except for lenses where there is significant shape distortion at the edges (i.e. very wide lenses) - but these are the IS is least needed in normal use. David SignatureDavid Littlewood >The release of Sony Alpha with the image stabilization in camera ( although >this is not new) highlighted the fundamental problem with Canon. [quoted text clipped - 9 lines] >lenses. >What do you guys think ? AIUI, the problem with in-camera IS is that the range of movement required in the chip is *much* greater than the movement required in an optical correction element in the middle of the lens. Thus, other things being equal, an in-lens system will always have the advantage, and be capable of being smaller, lighter, faster acting, or more effective (more f-stops effective benefit) or all of the above. The corollary is of course that you will need one in every lens, instead of just one in the body, but at least that one in each lens will be optimised for that lens, not constrained to some generic compromise value. So it is probably a choice of cheapness versus maximum effectiveness. I know which side I come down on, YMMV. David SignatureDavid Littlewood > The release of Sony Alpha with the image stabilization in camera ( > although this is not new) highlighted the fundamental problem with > Canon. There is no problem, that's just marketing hype. > Canon have had IS lenses long ago as it would be very difficult to do > in-camera stabilization in film cameras. The digital cameras had to > support older lenses including the ones with IS. If Canon developed a > camera with in-body stabilization it would hurt Canon sales and > reputation. Where do you get that idea? Canon has a good reputation as it stands, so how would adding another feature to the dozens of current features hurt their market share? Was Canons rep hurt when they introduced a sensor cleaner in the XTi? While we know the sensor cleaners are mostly hype, it doesn't seem to hurt image quality or camera performance, so how is it detrimental to sales? > What do you guys think ? I think you're an easy target for marketing campaigns. :-) > The release of Sony Alpha with the image stabilization in camera ( > although this is not new) highlighted the fundamental problem with Canon. [quoted text clipped - 10 lines] > lenses. > What do you guys think ? The lenses are doomed, the companies that make them are doomed, photography as we know it is doomed, we are all doomed. SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm [ . . . ] > The lenses are doomed, the companies that make them are doomed, > photography as we know it is doomed, we are all doomed. Now that's what I like to see. None of this namby-pamby "glass is half empty" rubbish. Neil >[ . . . ] >>> [quoted text clipped - 5 lines] > >Neil I'm on the way to the trash to throw away my 5D and the 24-105.... ;-) SignatureScott in Florida >> [ . . . ] >>> The lenses are doomed, the companies that make them are doomed, [quoted text clipped - 5 lines] > > ;-) Don't bother. As Skip pointed out, we're all doomed. Doomed, I tell ya, doomed! So it's no use. Signaturejohn mcwilliams >>> [ . . . ] >>>> The lenses are doomed, the companies that make them are doomed, [quoted text clipped - 8 lines] >Don't bother. As Skip pointed out, we're all doomed. Doomed, I tell ya, >doomed! So it's no use. <grin>.... SignatureScott in Florida >>[ . . . ] >>>> [quoted text clipped - 9 lines] > > ;-) But why? We're all doomed anyway, might as well enjoy our material stuff right up until the moment the sky falls. ;-) Neil >>>[ . . . ] >>>>> [quoted text clipped - 14 lines] > > Neil That's what I'm planning to do... SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm >>>[ . . . ] >>>>> [quoted text clipped - 14 lines] > >Neil You are, of course, correct. I just caught the trash guys in time..... ;-) Shoot on, 5D.... SignatureScott in Florida > > although this is not new) highlighted the fundamental problem with Canon. > > Canon have had IS lenses long ago as it would be very difficult to do [quoted text clipped - 15 lines] > -- > Skip Middletonwww.shadowcatcherimagery.comwww.pbase.com/skipm Good one, Skip -- Gator Bait <snip a bunch of words> > There is a very small advantage in having IS in the lens but it is not > significant enough to grant double and triple cost of the same quality > lenses. > What do you guys think ? I keep seeing this bandied about as the premium for IS/VR, but nowhere do I see it in actual practice. It is about a $400-500 increase in price over the non IS version, if such does exist in the lineup. The only times this has occurred is with the old 75-300, a cheap lens with a gimmick, as far as I am concerned, the 70-200 f2.8L ($1100 vs $1600) and the current 70-200 f4L ($600+ vs. $1100). Not exactly triple the price. When you get into the long teles, the price premium becomes such an insignificant part of the whole as to drop out of consideration, like with the 600mm f4L at more than $7000. So far, newer Canon IS lenses maintain their lead over sensor based IS, the 24-105 f4L and 70-200 f4L IS lenses give a minimum of 4 stops of correction. SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm > I keep seeing this bandied about as the premium for IS/VR, but nowhere do I > see it in actual practice. It is about a $400-500 increase in price over > the non IS version, if such does exist in the lineup. Canon's 8x25 IS Binoculars retail for $200 after rebate. While implementation complexity (& cost) will obviously vary, this does suggest at least that a low performance IS system has to cost less than $200. In general, I think that the "+$400-ish" rule of thumb is probably around the mark (retail), which means that anyone claiming "double", "triple", etc are only doing their comparisons based on one or two cheap lenses, rather than considering a broader range of IS lenses. -hh > <snip a bunch of words> >> There is a very small advantage in having IS in the lens but it is [quoted text clipped - 7 lines] > lineup. The only times this has occurred is with the old 75-300, a > cheap lens with a gimmick, as far as I am concerned I think it was more than a gimmick. I used that lens in Alaska in 1997, and it allowed decent shots that would have been total garbage without it. Was it a great optic, in strict optical terms? No. Did it render FAAAAR better captures than its non-IS sibling would have? Absolutely. --I was hanging out the window of engine-running shuttle-buses in Denali. -No tripod or monopod was possible. In situations like these, the lens was definitely worth having. I gave it to my dad, and he's happily shooting with it on his 10D... >, the 70-200 f2.8L > ($1100 vs $1600) and the current 70-200 f4L ($600+ vs. $1100). Not [quoted text clipped - 4 lines] > IS, the 24-105 f4L and 70-200 f4L IS lenses give a minimum of 4 stops > of correction. SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson >> <snip a bunch of words> >>> There is a very small advantage in having IS in the lens but it is [quoted text clipped - 16 lines] > definitely worth having. I gave it to my dad, and he's happily shooting > with it on his 10D... Maybe "gimmick" was too harsh of a word. It just seemed to me, at the time, that it was a cheap lens with IS added to justify getting a premium price. SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm >>> <snip a bunch of words> >>>> There is a very small advantage in having IS in the lens but it is [quoted text clipped - 20 lines] > the time, that it was a cheap lens with IS added to justify getting a > premium price. Partially, maybe. OK. But the price wasn't outlandish considering the tech it presented for the first time. What was the alternative for hand-held tele photography? The only alternatives at that point were very high dollar, large aperture lenses...or non-IS equiv. lenses that were nearly useless without eithe a tripod, or grainy film. This was a truly unique lens for its day. For its range, it allowed use of a slower lens without being tethered to a tripod. Beyond that, this was the lens that confirmed the whole concept of IS's usefulness. I think much like a prototype. Prototypes are never perfection, but they are the test and display of what is possible with new tech. As a prototype, it was very successful as it ushered in what has become serious a point of Canon influence over the industry. Everyone has had to adjust. Nikon with VR, Sigma is even trying...and now we've got every type of camera trying to sell based on some for of "IS." IS has changed the entire ballgame, and this lens started that. By the time I went mostly digital, I'd already replaced that lens with the 100-400 IS, so I don't have easily posted pictures taken with it... One of the few is this goofy monkey pic: http://www.pbase.com/markuson/image/47306239/original Nothing specatacular, but certainly not tirrible. SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson > the few is this goofy monkey pic: > http://www.pbase.com/markuson/image/47306239/original It's a good thing we're not on the planet of the apes. Calling an Orangutan a Monkey is grounds for a severe beating. :-) >> the few is this goofy monkey pic: >> http://www.pbase.com/markuson/image/47306239/original > >It's a good thing we're not on the planet of the apes. Calling an >Orangutan a Monkey is grounds for a severe beating. Or at the Unseen University on Discworld. David SignatureDavid Littlewood >>> the few is this goofy monkey pic: >>> http://www.pbase.com/markuson/image/47306239/original [quoted text clipped - 5 lines] > > David Ya, I thought of that, but alas...the send button was clicked...and I figured only the most anal among us would mind... :) SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson >>>> the few is this goofy monkey pic: >>>> http://www.pbase.com/markuson/image/47306239/original [quoted text clipped - 8 lines] >Ya, I thought of that, but alas...the send button was clicked...and I >figured only the most anal among us would mind... :) Oh, that must be me then. :-) David SignatureDavid Littlewood >>>>> the few is this goofy monkey pic: >>>>> http://www.pbase.com/markuson/image/47306239/original [quoted text clipped - 14 lines] > > David But...but... In Disney's animiated film "Jungle Book," King Orangutan even sings, "I'm tired of monkeying around...oh...ooh-bee-doo...I wanna be like you-hoo-hoo..." If HE says monkeying...then it must be OK. ;) SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson > <snip a bunch of words> >> There is a very small advantage in having IS in the lens but it is not [quoted text clipped - 4 lines] > I keep seeing this bandied about as the premium for IS/VR, but nowhere do I > see it in actual practice. That is because it does not exist. Among Nikon lenses VR is about a $200-$250 premium, not even 1/2 again as much as a comparable lens. the double and triple cost thing is more Sony disinformation. That company is beginning to irritate me some. Can't they do anything honestly? >> <snip a bunch of words> >>> There is a very small advantage in having IS in the lens but it is not [quoted text clipped - 12 lines] > to > irritate me some. Can't they do anything honestly? They seem incapable of it. They're beginning to seriously irritate me, too. SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm >>> <snip a bunch of words> >>>> There is a very small advantage in having IS in the lens but it is [quoted text clipped - 15 lines] > They seem incapable of it. They're beginning to seriously irritate > me, too. They've irritated me for a long time. It was with clenched teeth that I finally broke down and bought their uniquely small/powerful/light SZ notebook computer, which makes for what I think is the perfect travel/flight laptop. I'm very computer savvy, and yet the couple times I had to deal with their customer service/tech support, I was literally BLOWN AWAY with their lack of professionalism and knowledge--even at their "second tier" level of "support." I found that *I* was *educating THEM* about their own product, because my (to me) basic research in shopping meant I knew more about it than they did. Truly pathetic on their end. I love the laptop, though. SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson > The release of Sony Alpha with the image stabilization in camera ( although > this is not new) highlighted the fundamental problem with Canon. [quoted text clipped - 9 lines] > lenses. > What do you guys think ? I can't find the article but I remember reading about the comparison between in-camera IS and in-lens IS. It stated that the in-camera IS would prevent a full sized sensor from working with the in-camera IS. It stated that the camera would be very large to allow for full sensor movement and the light from the lens could fall off the edges of the sensor, therefore even a larger then full sensor was needed, thus making the camera even larger. Am I blowing smoke or does anyone else remember this? SignatureLen > I can't find the article but I remember reading about the comparison > between in-camera IS and in-lens IS. It stated that the in-camera IS [quoted text clipped - 5 lines] > > Am I blowing smoke or does anyone else remember this? It's quite obvious if you think about it. The lens throws a circular, fixed-size image into the camera. The size of this image circle is designed to cover the film frame (or sensor, obviously) and not a smidgeon more than necessary- or, if the image circle size IS significantly bigger than the film frame you will have to carry around a lens that is correspondingly larger, heavier and more expensive than would otherwise be the case. Now, with in-camera IS the sensor has to move around to "chase" the image as it wobbles around the sensor plane as your hands shake. The image circle is of course constant and stays in place, so the sensor has a hard limit on how far it can move in any direction before parts of it actually pokes out into the darkness outside the image circle. So, in-body IS is a good idea only as long as the image circle is sufficiently larger than the sensor. A full-frame sensor on a full-frame lens is a particularly bad candidate for in-body IS, an APS-sized sensor on a "digital" APS-sized lens with reduced image circle size ain't too hot a proposition either. Full-frame lens and APS-sized sensor gives you the most leeway. Compare this to an IS lens, which de facto lets the image circle chase the wobbling image so that it stays in the same place relative to the sensor. >> I can't find the article but I remember reading about the comparison >> between in-camera IS and in-lens IS. It stated that the in-camera IS [quoted text clipped - 12 lines] >film frame you will have to carry around a lens that is correspondingly >larger, heavier and more expensive than would otherwise be the case. It's not at all obvious. It very much depends on focal length, of course. But for medium telephoto and onwards (say 200mm focal length and upwards) the size of the image circle has very little effect on lens size and weight. A 300mm/f4 for a 6x7 camera is just about identical in all dimensions to a 300mm/f4 for a 35mm body, and costs just about the same. The determining factor for size (and weight, and cost) is the fromt element. Mind you, a 50mm lens for a 6x7 system *will* be larger/heavier/costlier than a 50mm lens for a 35mm camera. > Compare this to an IS lens, which de facto lets the image circle chase the > wobbling image so that it stays in the same place relative to the sensor. In fact the displacement in IS lenses does cause loss of illumination (asymmetrical vignetting) as well as localised aberrations. One of the main arguments against using IS lenses is that at the best (IS turned off) they may not entirely match the performance of similar non-IS designs, and at the worst (moving element or group at maximum displacement) optical performance will be visibly compromised. One slightly ironic point is that so far all the sensor-stabilised cameras have been 1.5X APS factor. In practice, even lenses like the 11-18mm and 10-20mm wide angles provide 2mm or more coverage beyond this at their shortest setting - the Tamron 11-18mm will cover full frame at 13-14mm. Yet Canon uses 1.6X sensors, which would be even better (more room to move round!) with sensor-based IS than the 1.5X format. The only lens I know which causes problems with sensor-based IS on the KM/Sony 1.5X bodies is the Sigma 30mm f1.4 - it was, I think, really designed to work on Canon 1.6X or Sigma 1.7X sensors, and it's already pushing its coverage on 1.5X when wide open. David [ . . . ] > One slightly ironic point is that so far all the sensor-stabilised cameras > have been 1.5X APS factor. [ . . . ] Off topic for the thread, but this is the first time I've seen that term, "APS factor," used. I think it's a very good one, much better than the common "crop factor" (and variants) which I have always objected to on the grounds that nothing is actually being cropped, and even if it were, nothing is being *multiplied* by the so-called crop and the 1.5x or other number given is obviously a multiplier. "APS factor" is very good. Neil >[ . . . ] >> [quoted text clipped - 9 lines] > >"APS factor" is very good. I agree with your disagreements, but some complain bitterly about using APS to describe these sensor sizes, because the sizes don't exactly agree. See http://tinyurl.com/somes KS >[ . . . ] >> [quoted text clipped - 9 lines] > >"APS factor" is very good. Well, up to a point, Lord Copper. The reference to APS indicates that the sensor is the same size as APS film (more specifically, IIRC, APS-C). This is decidedly specific; there are many other sensor sizes in use in digital cameras, so the term would not do for a general case. Would be a lot more rigorous if the exact sensor size in mm were to be quoted. David SignatureDavid Littlewood >>[ . . . ] >>> [quoted text clipped - 13 lines] >> > Well, up to a point, Lord Copper. Now that sent me to Google to find out who Lord Copper was. > The reference to APS indicates that the sensor is the same size as APS > film (more specifically, IIRC, APS-C). Well, up to a point, Lord Copper. (dang, that's handy already.) APS-C, yes, but not *exactly* the APS-C size in any digital SLR as far as I know. Since it's inexact in the first place, and there are at least two other APS sizes in the second place, "APS factor" should be understood to be taken somewhat loosely. As I'm sure you know, the APS factor is about 1.5x for Nikons and about 1.6x for the majority of Canons. I'm aware that there are some other dSLR formats smaller than "full frame" too, but don't know (or care) much about 'em. As long as the sensor size is within the general ballpark of some APS format, the term seems good enough -- particularly when used with the multiplier number, which does make it more specific. > This is decidedly specific; there are many other sensor sizes in use in > digital cameras, so the term would not do for a general case. Not for digital cameras in general, most of which have much tinier sensors, but for dSLRs of less than "full frame." I'm only suggesting that "APS factor" is a huge improvement on the rather silly term "crop factor" or any variation on that. People who use "crop factor" do so only in connection with dSLRs, as far as I'm aware. There isn't any obvious reason to use any such term for cameras without interchangeable lenses. > Would be a lot more rigorous if the exact sensor size in mm were to be > quoted. But that wouldn't even begin to serve the same purpose. When people say "crop factor" what they really mean is the multiplier needed to convert the actual focal length to 35mm equivalency. It's not a crop factor (whatever that might mean) at all that they're talking about. How, for example, could you crop anything by 1.5 times? You can't crop 150% of something. Some folks used to call it a "focal length multiplier," which is not really bad, but was objected to by nitpickers on the grounds that the focal length wasn't actually multiplied. "APS factor" dodges that complaint neatly and seems to me a very good solution. It's certainly handier than, say, "multiplier for converting actual focal length into 35mm equivalency." If you can't even get people to say "fixed focal length" when that's what they mean, you'd never get them to say *that*. Neil >>>[ . . . ] >>>> [quoted text clipped - 20 lines] > >Well, up to a point, Lord Copper. (dang, that's handy already.) Glad you like it! It's a very funny book, BTW. >APS-C, yes, but not *exactly* the APS-C size in any digital SLR as far as I >know. Since it's inexact in the first place, and there are at least two [quoted text clipped - 5 lines] >ballpark of some APS format, the term seems good enough -- particularly when >used with the multiplier number, which does make it more specific. I realise there is more than one APS size, that is why I referred specifically to APS-C; this is the format generally understood to be meant when a reference is made to APS-sized sensors. As for the lack of exact correspondence, this simply increases my conviction that it is not really a good term to use in this context. >> This is decidedly specific; there are many other sensor sizes in use in >> digital cameras, so the term would not do for a general case. [quoted text clipped - 5 lines] >with dSLRs, as far as I'm aware. There isn't any obvious reason to use any >such term for cameras without interchangeable lenses. To me, that just confirms that the kind of sloppy usage involved is bound to result in a messy compromise or inconsistency at some point in the logic chain. >> Would be a lot more rigorous if the exact sensor size in mm were to be >> quoted. [quoted text clipped - 4 lines] >that might mean) at all that they're talking about. How, for example, could >you crop anything by 1.5 times? You can't crop 150% of something. Factors - ratios - can be denominators as well as numerators, especially in the hands of those to whom linguistic precision is some kind of offence. We are all familiar with this in the usage f/1.4, which many people sloppily quote as f1.4. We just have to get used to it. >Some folks used to call it a "focal length multiplier," which is not really >bad, but was objected to by nitpickers on the grounds that the focal length >wasn't actually multiplied. Personally don't see why a term is required. It's an image size ratio, everything else works as before; why not call it image size ratio? Better, since the "ratio" is to a film format which will become increasingly irrelevant to new generations of photographers, eventually it will be enough to just quote size, as I said >"APS factor" dodges that complaint neatly and seems to me a very good >solution. It's certainly handier than, say, "multiplier for converting >actual focal length into 35mm equivalency." If you can't even get people to >say "fixed focal length" when that's what they mean, you'd never get them to >say *that*. Sorry, Neil; we'll have to agree to differ on this one. IMO, to refer to the ratio between a given sensor size and a 35mm film (36x24mm) by using a term which is in fact the name of a particular film format (and not even the one being compared) is not just confusing, it's downright perverse. David SignatureDavid Littlewood >>> In article <PfedncnUasyDXTrYnZ2dnUVZ_ragnZ2d@comcast.com>, Neil >>> Harrington [quoted text clipped - 28 lines] >> > Glad you like it! It's a very funny book, BTW. In fact, last night I checked my local library's online catalog and I see they have a copy. I mean to take it out, perhaps this weekend. Thanks for pointing me to it. >>APS-C, yes, but not *exactly* the APS-C size in any digital SLR as far as >>I [quoted text clipped - 15 lines] > As for the lack of exact correspondence, this simply increases my > conviction that it is not really a good term to use in this context. But a) it's close enough, especially since without the "-C" it's vague as to exact dimensions, and b) it has already achieved considerable currency. I can never remember the exact dimensions anyway, only that it's a bit less in area than a half-frame 35. >>> This is decidedly specific; there are many other sensor sizes in use in >>> digital cameras, so the term would not do for a general case. [quoted text clipped - 11 lines] > to result in a messy compromise or inconsistency at some point in the > logic chain. But how? Since it's almost always going to be used with the specific multiplier -- "APS factor 1.5x" or whatever -- just as the nonsensical "crop factor" is now, how is it messy or inconsistent? >>> Would be a lot more rigorous if the exact sensor size in mm were to be >>> quoted. [quoted text clipped - 11 lines] > offence. We are all familiar with this in the usage f/1.4, which many > people sloppily quote as f1.4. We just have to get used to it. Well, *we* convert that to f/1.4 in our minds when we read it. It only lacks the virgule to be correct. But whether you take "crop factor" to mean a denominator or a numerator it makes no sense when used as it is used. Nothing is cropped by 1.5 times, and nothing is cropped by 1/1.5 either. That should mean *removing* two thirds, not *leaving* two thirds. And linear, or in area? Now there's messiness for you. >>Some folks used to call it a "focal length multiplier," which is not >>really [quoted text clipped - 7 lines] > irrelevant to new generations of photographers, eventually it will be > enough to just quote size, as I said You do have a point on the increasing irrelevance of 35mm. I agree with that, but for the time being and probably some considerable time to come, we are used to thinking of magnification and angles of view in terms of familiar 35mm focal lengths and those numbers are useful for that reason. It may be the case that the equivalency will long outlast the source and even become permanent, so that for example "35-105mm equiv." will convey the idea of a certain range of angles of view for users who have never used or seen an actual 35-105mm lens, including your new generations of photographers. Stranger things have happened. After all, in compact cameras it is standard practice to describe sensor sizes in video tube terms, even though that's completely irrelevant to compact camera use and the number given is meaningless as far as the actual sensor dimensions are concerned. And this appears to be a permanent practice. >>"APS factor" dodges that complaint neatly and seems to me a very good >>solution. It's certainly handier than, say, "multiplier for converting [quoted text clipped - 8 lines] > term which is in fact the name of a particular film format (and not even > the one being compared) is not just confusing, it's downright perverse. Well, the alternative then is what? You suggest just quoting size, but there are so many sizes -- at least four sub-"full frame" sizes in dSLRs, several more (the so-called 2/3 type, 1/1.8, 1/2.5, 1/2.7, . . .) in compact and ultracompact cameras. This is a problem that we never had in 35mm, which unless otherwise specified was always assumed to be 24x36. Where "APS size" is used, it seems to be used only in connection with dSLRs having either the 1.5x or 1.6x f.l. equivalency factor. So when you speak of quoting size, how exactly would you do that? My Nikon dSLRs I think are 15.something by 23.something. What size would you call that? I know most Canons are slightly smaller. Would you call them "Nikon size" and "Canon Rebel size," something like that? Neither of those really serves the purpose the user most wants: what the actual focal lengths he may use will mean in terms that are familiar to him. Neil ------- Cut, on sensor and lens multiplier or divider --------- >Personally don't see why a term is required. It's an image size ratio, >everything else works as before; why not call it image size ratio? >Better, since the "ratio" is to a film format which will become >increasingly irrelevant to new generations of photographers, eventually >it will be enough to just quote size, as I said Why not quote the angle of view that the lens gives with the sensor? Most users are not interested in the focal length per se. I realise that macro work and photometry can require more than the angle of view. SignatureIan G8ILZ There are always two people in every picture: the photographer and the viewer. ~Ansel Adams > ------- Cut, on sensor and lens multiplier or divider --------- > [quoted text clipped - 7 lines] > users are not interested in the focal length per se. I realise that macro > work and photometry can require more than the angle of view. And long lenses require more too. You're quite right, angle of view is the important thing -- but only with normal to wide-angle lenses. Users could in time get used to the idea that "28mm equivalent" meant "75 degrees corner to corner" and end up just calling such a lens a 75-degree lens. There is a small fly in that ointment, in that third-party lenses made in more than one mount would be slightly different on a Nikon than on a Canon, 1.5x and 1.6x focal length multipliers respectively and the necessary adjustments to angle, but those adjustments in most cases would be small. With long lenses however it's the magnification that the user is interested in, not the angle of view. Sure, one is necessarily related to the other, but for example calling a 200-400mm zoom a 12-degree-20-minute-to-6-degree-10-minute lens gets a little unwieldy, isn't very informative for most users -- and is only correct for the 24x36 format anyway. So I think using an appropriate multiplier to relate sensor focal lengths to some familiar standard continues to be useful, and while there's nothing cosmically significant about the 35mm format at least it is a familiar standard, and by far the most familiar one. Neil >> ------- Cut, on sensor and lens multiplier or divider --------- >> [quoted text clipped - 23 lines] >very informative for most users -- and is only correct for the 24x36 format >anyway. Magnification depends on the focal distance as well as the focal length, it is independent of the "multiplier factor". For macro you are interested in the angle of view and the focal distance, which is why I said that "I realise that macro work and photometry can require more than the angle of view". >So I think using an appropriate multiplier to relate sensor focal lengths to >some familiar standard continues to be useful, and while there's nothing >cosmically significant about the 35mm format at least it is a familiar >standard, and by far the most familiar one. It is a convenience that most people will understand, I made my suggestion half in jest, with far more variation in sensor size than there was in film size it becomes important to know that there is more than focal length to consider, although most of the cameras have fixed lens without any focal length marks it is probably not a great problem. SignatureIan G8ILZ There are always two people in every picture: the photographer and the viewer. ~Ansel Adams >>> ------- Cut, on sensor and lens multiplier or divider --------- >>> [quoted text clipped - 35 lines] > > Magnification depends on the focal distance as well as the focal length, Sure, but "near infinity" is generally understood when comparing focal lengths for purposes of magnification. > it is independent of the "multiplier factor". For macro you are interested > in the angle of view and the focal distance, which is why I said that "I [quoted text clipped - 11 lines] > film size it becomes important to know that there is more than focal > length to consider, As long as the lens factor used is correct, it takes care of the differences in sensor size for the purposes most users are interested in, i.e. magnification or angle of view. > although most of the cameras have fixed lens without any focal length > marks it is probably not a great problem. Just so, but users still want to know what the focal length range is in terms of some familiar standard. There's no reason of cosmic importance for 24 x 36 to be that standard, other than the fact that it is by far the most familiar one. Neil >>>> ------- Cut, on sensor and lens multiplier or divider --------- >>>> [quoted text clipped - 38 lines] >Sure, but "near infinity" is generally understood when comparing focal >lengths for purposes of magnification. Only in a crudely qualitative sense; thing "near infinity" are arbitrarily small, magnifying them only serves to make them arbitrarily larger. >> it is independent of the "multiplier factor". For macro you are interested >> in the angle of view and the focal distance, which is why I said that "I [quoted text clipped - 15 lines] >in sensor size for the purposes most users are interested in, i.e. >magnification or angle of view. I wonder how many users of compact cameras know or care what the focal length is, using the view finder to obtain the view required is the principle interest. The users of DSLRs will make a purchases based on their requirement taking account of the 'lens correction factor', and then frame with the viewfinder having little regard for the focal length. >> although most of the cameras have fixed lens without any focal length >> marks it is probably not a great problem. [quoted text clipped - 3 lines] >24 x 36 to be that standard, other than the fact that it is by far the most >familiar one. Indeed, as a comparison for relative angle of view it is most useful, and I do use it, but what of DoF? SignatureIan G8ILZ There are always two people in every picture: the photographer and the viewer. ~Ansel Adams >>> In article <h-WdnVy7dYo6NzTYnZ2dnUVZ_u-unZ2d@comcast.com>, Neil >>> Harrington [quoted text clipped - 93 lines] > Indeed, as a comparison for relative angle of view it is most useful, and > I do use it, but what of DoF? >>> In article <h-WdnVy7dYo6NzTYnZ2dnUVZ_u-unZ2d@comcast.com>, Neil >>> Harrington [quoted text clipped - 78 lines] > length is, using the view finder to obtain the view required is the > principle interest. For the majority of 'em I'm sure you're right. For those of us used to the idea of choosing different focal lengths though, the equivalent focal length range of even an ultracompact is of primary importance and interest. The *actual* focal length range is not. The users of DSLRs will make a purchases based on > their requirement taking account of the 'lens correction factor', and then > frame with the viewfinder having little regard for the focal length. [quoted text clipped - 11 lines] > Indeed, as a comparison for relative angle of view it is most useful, and > I do use it, but what of DoF? DoF is different, of course. But I think that's secondary for most users most of the time, in choosing a focal length. The *difference* in DoF for dSLRs I think is relatively small, especially since the greater magnification for the final print cancels some of the difference out. Neil > DoF is different, of course. But I think that's secondary for most users > most of the time, in choosing a focal length. The *difference* in DoF for > dSLRs I think is relatively small, especially since the greater > magnification for the final print cancels some of the difference out. Different? If you put a 50mm lens on a camera the DOF will be the same whatever film/sensor is fitted. > > DoF is different, of course. But I think that's secondary for most users > > most of the time, in choosing a focal length. The *difference* in DoF for [quoted text clipped - 4 lines] > If you put a 50mm lens on a camera the DOF will be the same whatever > film/sensor is fitted. No, the DOF will be smaller for a smaller sensor/film format, all else equal. This is because DOF is defined on a print, and to obtain the same sized print from two sensors of different sizes, the image from the smaller one must be enlarged more, thus enlarging the circle of confusion more. In other words, a smaller sensor needs a smaller circle of confusion, so the DOF is smaller, if all else (focal length, aperture etc) is equal. I hope this time the thread does not degenerate into a stupid argument (please think about this before saying it's wrong!). >> > DoF is different, of course. But I think that's secondary for most >> > users [quoted text clipped - 17 lines] > I hope this time the thread does not degenerate into a stupid argument > (please think about this before saying it's wrong!). Your definition of DOF depends on viewing distance from the print. Think about it. 8-) > Your definition of DOF depends on viewing distance from the print. > Think about it. 8-) Hi. I have. It's not my definition, it's the one used for the markings on your lenses and for DOF calculators. It is the one used in books etc. >> > DoF is different, of course. But I think that's secondary for most users >> > most of the time, in choosing a focal length. The *difference* in DoF for [quoted text clipped - 12 lines] >of confusion, so the DOF is smaller, if all else (focal length, >aperture etc) is equal. I agree with this. DOF is smaller in the smaller sensor camera when the aperture, focal length, and subject-sensor distance are the same. However, all is not equal. The images captured differ because the angles of view differ. If the two cameras are set up for the same angle of view, then the smaller sensor camera has more DOF at the same aperture. The DOF will be about the same when the smaller sensor camera lens is opened one stop. KS >> DoF is different, of course. But I think that's secondary for most users >> most of the time, in choosing a focal length. The *difference* in DoF for [quoted text clipped - 4 lines] > If you put a 50mm lens on a camera the DOF will be the same whatever > film/sensor is fitted. For all practical purposes, DoF is something that exists on the print (or other final image), not on the sensor. The more you enlarge the image, the more depth of field shrinks -- because you're enlarging the CoC along with everything else. So since the image from a smaller sensor must be enlarged more, the DoF of the lens used with it is smaller, assuming of course the same size final image. On the other hand, its DoF is *greater* than a lens of the 35mm equivalent f.l. That is, the DoF of a 50mm lens on a dSLR with 1.5x conversion factor will be less than that of the same lens on a 35 (same distance, aperture etc. assumed) but greater than that of the 75mm lens that it's "equivalent" to. Neil > Just so, but users still want to know what the focal length range is in > terms of some familiar standard. There's no reason of cosmic importance for > 24 x 36 to be that standard, other than the fact that it is by far the most > familiar one. And that's why it's the standard, but not a cosmic one. Signaturejohn mcwilliams > Why not quote the angle of view that the lens gives with the sensor? > Most users are not interested in the focal length per se. I realise that > macro work and photometry can require more than the angle of view. Yes, that seems like a good idea. Call an angle an angle and a focal length a focal length. Stating everything relative to 35mm full-frame is silly, especially if it's not even what most people use. Signature--Bryan >> Why not quote the angle of view that the lens gives with the sensor? Most >> users are not interested in the focal length per se. I realise that macro [quoted text clipped - 5 lines] > Stating everything relative to 35mm full-frame is silly, especially > if it's not even what most people use. Well, with so many sensor sizes, and proportions, on the market, 35mm probably seems like the best to pick for a standard, since most of the digital cameras, both point and shoot and DSLR, are similar in size, or at least started out that way, to 35mm film cameras. And, originally, most of the customers who migrated to digital came there from 35mm film. What standard would you propose? SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm >>> Why not quote the angle of view that the lens gives with the sensor? >>> Most users are not interested in the focal length per se. I realise that [quoted text clipped - 11 lines] > least started out that way, to 35mm film cameras. And, originally, most > of the customers who migrated to digital came there from 35mm film. . . . Exactly. And I think that even long after 35mm is dead and gone, its use as a familiar standard for focal lengths will probably go on and on. It's already *the* standard of comparison for focal length conversions, and once such a standard is established there's no obvious reason to change it. Neil > Exactly. And I think that even long after 35mm is dead and gone, its use > as a familiar standard for focal lengths will probably go on and on. It's > already *the* standard of comparison for focal length conversions, and > once such a standard is established there's no obvious reason to change > it. You can't just convert the focal length and come up with the correct answer. Not every lens characteristic changes when you change sensor size. Things like the DOF stay the same. They only change if you move the camera or zoom to reflect the change in field of view. >> Exactly. And I think that even long after 35mm is dead and gone, its use >> as a familiar standard for focal lengths will probably go on and on. It's [quoted text clipped - 8 lines] > They only change if you move the camera or zoom to reflect the change in > field of view. Actually, I believe DOF is different, but, otherwise, everything else, like perspective, stays the same. SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm >>> Exactly. And I think that even long after 35mm is dead and gone, its use >>> as a familiar standard for focal lengths will probably go on and on. It's [quoted text clipped - 11 lines] >Actually, I believe DOF is different, but, otherwise, everything else, like >perspective, stays the same. The perspective depends on where you stand relative to the scene; neither the size of the sensor nor the length of the lens, real or pretend, can effect it. SignatureIan G8ILZ There are always two people in every picture: the photographer and the viewer. ~Ansel Adams >>>> Exactly. And I think that even long after 35mm is dead and gone, its >>>> use [quoted text clipped - 18 lines] > the size of the sensor nor the length of the lens, real or pretend, can > effect it. Funny, I think that's what I said. SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm >>> Exactly. And I think that even long after 35mm is dead and gone, its use >>> as a familiar standard for focal lengths will probably go on and on. [quoted text clipped - 11 lines] > Actually, I believe DOF is different, but, otherwise, everything else, > like perspective, stays the same. No. All you have effectively done is put a mask over the film. Unless you actually move it all stays the same, just less of the scene. >> Actually, I believe DOF is different, but, otherwise, everything else, >> like perspective, stays the same. > > No. > All you have effectively done is put a mask over the film. > Unless you actually move it all stays the same, just less of the scene. Yes, the image on the sensor is the same as that part of the image from the lens regardless, of course. However, the visual depth of field *in a print* (or screen display, or whatever) also depends on the size of the print (that is, on the degree of enlargement). If you're making 8x10 prints of everything, the print from the small sensor will be enlarged more than the print from the larger sensor/film, and will hence show less depth of field. >>>> Exactly. And I think that even long after 35mm is dead and gone, its >>>> use as a familiar standard for focal lengths will probably go on and [quoted text clipped - 15 lines] > All you have effectively done is put a mask over the film. > Unless you actually move it all stays the same, just less of the scene. Not really. You need to remember that the smaller image has to be enlarged more to fill the same size final print, which reduces the DoF. Neil >> Exactly. And I think that even long after 35mm is dead and gone, its use >> as a familiar standard for focal lengths will probably go on and on. It's [quoted text clipped - 4 lines] > You can't just convert the focal length and come up with the correct > answer. Sure you can, as far as the resulting magnification and angle of view is concerned. > Not every lens characteristic changes when you change sensor size. > Things like the DOF stay the same. > They only change if you move the camera or zoom to reflect the change in > field of view. No, DoF changes too, though not in the same degree. Neil >> Not every lens characteristic changes when you change sensor size. >> Things like the DOF stay the same. >> They only change if you move the camera or zoom to reflect the change in >> field of view. > >No, DoF changes too, though not in the same degree. Right, you get about 1 stop DoF advantage with the APS-C-type sensors compared to 35 mm. KS >>> Not every lens characteristic changes when you change sensor size. >>> Things like the DOF stay the same. [quoted text clipped - 7 lines] > > KS That depends on what you're after. Sometimes limited DOF is what you want...and sometimes the reverse is true... SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson >>> Not every lens characteristic changes when you change sensor size. >>> Things like the DOF stay the same. [quoted text clipped - 7 lines] > > KS Or disadvantage, depending on what you want. If you want less, then 35mm has the advantage, if you want more, 1.5x has the advantage, unless you merely stop the 35mm down...much easier to get more depth of field from a full frame sensor than it is less depth of field from a crop sensor. SignatureSkip Middleton www.shadowcatcherimagery.com www.pbase.com/skipm >>> Not every lens characteristic changes when you change sensor size. >>> Things like the DOF stay the same. [quoted text clipped - 5 lines] >Right, you get about 1 stop DoF advantage with the APS-C-type sensors >compared to 35 mm. Or disadvantage if you are trying to isolate the subject. SignatureIan G8ILZ There are always two people in every picture: the photographer and the viewer. ~Ansel Adams >>> Not every lens characteristic changes when you change sensor size. >>> Things like the DOF stay the same. [quoted text clipped - 4 lines] > Right, you get about 1 stop DoF advantage with the APS-C-type sensors > compared to 35 mm. You get that by using a smaller aperture. A shorter lens will have the same speed at a proportionally smaller aperture. The the total light falling in frame will be the same, so it's not the advantage it might appear. If you want the larger depth-of-field but have the larger sensor, you could either: Use the shorter lens smaller aperture, and crop down to the center of the image, just as happens with the smaller sensor. Use the longer focal length, but up ISO and stop down. The same amount of light falls on sensor. Signature--Bryan >> Not every lens characteristic changes when you change sensor size. >> Things like the DOF stay the same. >> They only change if you move the camera or zoom to reflect the change in >> field of view. > > No, DoF changes too, though not in the same degree. No, it can't. The formulae for DOF doesn't know what size the sensor is. It is purely the distance to the subject, the *real* focal length and the aperture. I.e. a 50mm lens gives the same DOF on any format. >>> Not every lens characteristic changes when you change sensor size. >>> Things like the DOF stay the same. [quoted text clipped - 7 lines] > aperture. > I.e. a 50mm lens gives the same DOF on any format. This is blatantly false; the circle of confusion is a key input to the DOF calculation. And when picking your acceptable circle of confusion, you have to take into account the degree of enlargement you planned for the image. The markings on lenses, or standard tables, are based on commonly accepted circle of confusion values which are in turn based on common enlargement sizes; they're not any kind of physical absolute. >>> Not every lens characteristic changes when you change sensor size. >>> Things like the DOF stay the same. [quoted text clipped - 4 lines] > > No, it can't. It can, it must, and it does. > The formulae for DOF doesn't know what size the sensor is. > It is purely the distance to the subject, the *real* focal length and the > aperture. Wrong. It is also the degree of final enlargement (the more the enlargement, the less the DoF) and the viewing distance (the greater the viewing distance, the greater the DoF). The formulas *always* make certain assumptions about these things. If you understood how the formulas are derived in the first place you would know this. > I.e. a 50mm lens gives the same DOF on any format. That's not only wrong for the reasons I just stated, it's not even true from one country to another. Take a look at the DoF scales engraved on a 50mm Nikon lens and a 50mm Leica lens. They are not even nearly the same, the Nikon 50 showing substantially less DoF than the Leica 50 at the same aperture and distance. How can that be? Simple: German lens makers use a more generous CoC in their calculations. It's all in the assumptions, you see. DoF is not something that's set in stone as you seem to think. Neil |
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