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Photo Forum / Digital Photography / DSLR Cameras / December 2006"Hybrid" or polycarbonate lenses and aging
Two main factors result in aging (weakening, hazing and yellowing) of polycarbonate lens material. 1. UV light exposure. 2. Mechanical stress (internal or external). With new camera lenses, particularly inexpensive "kit" lenses utilizing plastics in standalone or hybrid lens designs, the vulnerability of the plastic should be kept in mind. Exposure to UV can cause aging of the lens material to the point where detail is reduced in images (because of hazing) and light throughput drops by 5%, effectively nullifying the increased throughput provided by the use of anti-reflection coatings. Though this does not increase surface reflectivity, it does increase internal scattering. These changes are the result of broken molecular bonds in the plastic material itself. Glass is unaffected by UV light exposure and less effected by mechanical stress. However, plastic moulded elements are far cheaper to produce than glass aspherics which must be moulded and ground or ground from the blank stage. Interestingly, the effects of aging on plastic are similar to the effects caused when mold that has adhered to glass elements in camera lenses that have been exposed to moisture and stored in darkness before being allowed to dry out. > Two main factors result in aging (weakening, hazing and yellowing) of > polycarbonate lens material. <moronic banter snipped> Get on that one-trick pony and ride. >Two main factors result in aging (weakening, hazing and yellowing) of >polycarbonate lens material. >1. UV light exposure. Adding a UV inhibitor to the optical resin will reduce yellowing, and using this material on the internal lens elements should eliminate any UV exposure. Also, I would imaging you could off-set any "yellowing" by adjusting the white balance. >2. Mechanical stress (internal or external). Have you seen what happens when a glass lens is subjected to mechanical stress? >With new camera lenses, particularly inexpensive "kit" lenses utilizing >plastics in standalone or hybrid lens designs, the vulnerability of the >plastic should be kept in mind. Can you give an example of a lens that uses plastic lens elements? >Exposure to UV can cause aging of the lens material to the point where >detail is reduced in images (because of hazing) and light throughput >drops by 5%, effectively nullifying the increased throughput provided >by the use of anti-reflection coatings. Before I share your concern I would like to know the amount of UV exposure needed to cause a plastic lens element to degrade significantly. So please state your source for this information. Also, please provide the UV Exposure / Degradation Curve, and whether the entire UV wavelength considered or just certain bands. TR > >Two main factors result in aging (weakening, hazing and yellowing) of > >polycarbonate lens material. [quoted text clipped - 4 lines] > UV exposure. Also, I would imaging you could off-set any "yellowing" > by adjusting the white balance. To a degree you can. But you can't recover the light loss through filtration. > >2. Mechanical stress (internal or external). > > Have you seen what happens when a glass lens is subjected to > mechanical stress? Sure, but it is far less prone deformation due to force stress than plastic. Put a piece of plastic and a piece of glass between two polarizers and see which show the most deformation with force. Some plastic already has problems internally because you can anneal it like a glass lens element. > >With new camera lenses, particularly inexpensive "kit" lenses utilizing > >plastics in standalone or hybrid lens designs, the vulnerability of the > >plastic should be kept in mind. > > Can you give an example of a lens that uses plastic lens elements? Tamron's new 18-50mm f2.8. Uses a hybrid (glass-plastic cemented element). > >Exposure to UV can cause aging of the lens material to the point where > >detail is reduced in images (because of hazing) and light throughput [quoted text clipped - 4 lines] > exposure needed to cause a plastic lens element to degrade > significantly. Hundreds of sunny days worth I'd guess. > So please state your source for this information. Also, please provide > the UV Exposure / Degradation Curve, and whether the entire UV > wavelength considered or just certain bands. Source is myself. I haven't read about it in years. > TR >> >Two main factors result in aging (weakening, hazing and yellowing) of >> >polycarbonate lens material. [quoted text clipped - 7 lines] >To a degree you can. But you can't recover the light loss through >filtration. BFD. So you lose a (small) fraction of an f-stop. >Tamron's new 18-50mm f2.8. Uses a hybrid (glass-plastic cemented >element). Not familiar with this lens. Surprised that Tamron would come out with a new lens in this range/speed when earlier in the year it released the 17-50mm f/2.8 XR Di II LD. The reviews I've seen of this lens have all been very favorable. If you're talking about the 17-50mm f/2.8 XR Di II LD, have you seen ANYTHING that might indicate it will be prone to the sort of problems you've indicated? Or are you just making this up? >> >Exposure to UV can cause aging of the lens material to the point where >> >detail is reduced in images (because of hazing) and light throughput [quoted text clipped - 6 lines] > >Hundreds of sunny days worth I'd guess. Constant exposure to hundreds of sunny days? Is it more severe at lower latitudes and/or higher elevations? Will a Skylight Filter reduce the effect? Does this UV exposure also degrade intraocular lenses, prescription lenses, and protective eyewear? Or are you just making this up? >> So please state your source for this information. Also, please provide >> the UV Exposure / Degradation Curve, and whether the entire UV >> wavelength considered or just certain bands. > >Source is myself. I haven't read about it in years. Oh, so you're making it up. Pardon my French, but IMO you have 'yeux bruns'. TR > Constant exposure to hundreds of sunny days? Is it more severe at > lower latitudes and/or higher elevations? Will a Skylight Filter > reduce the effect? One would think that a good UV filter would block ultraviolet light from passing through the lens elements, and thus guard against discoloration. I have read that Tiffen, of all people, make a filter that is far more effective at blocking UV than most other brands that make UV filters. I cannot recall which filter is Tiffen's star UV blocker, but perhaps someone else can tell us. > >> >Two main factors result in aging (weakening, hazing and yellowing) of > >> >polycarbonate lens material. [quoted text clipped - 9 lines] > > BFD. So you lose a (small) fraction of an f-stop. Then why not go burnish the coatings off your lenses if you don't need it? They are softer than glass and you can avoid scratches in cleaning by doing that. > >Tamron's new 18-50mm f2.8. Uses a hybrid (glass-plastic cemented > >element). [quoted text clipped - 7 lines] > ANYTHING that might indicate it will be prone to the sort of problems > you've indicated? Or are you just making this up? That's the lens. It's too early to see any problems since the lens is new. How long do you intend to keep it? 10 years, 20? Think it will last as long as a manual all glass and metal lens? Not likely. > >> >Exposure to UV can cause aging of the lens material to the point where > >> >detail is reduced in images (because of hazing) and light throughput [quoted text clipped - 15 lines] > > Or are you just making this up? Polycarbonate is particularly sensitive to this. > >> So please state your source for this information. Also, please provide > >> the UV Exposure / Degradation Curve, and whether the entire UV [quoted text clipped - 6 lines] > > TR Yes, between the time I read about it and now, they invented a new, magic polycarbonate that has a completely different chemical structure. Honest. Keep whistling in your plastic camera graveyard. > Two main factors result in aging (weakening, hazing and yellowing) of > polycarbonate lens material. [quoted text clipped - 15 lines] > adhered to glass elements in camera lenses that have been exposed to > moisture and stored in darkness before being allowed to dry out. Hey Rich, you have a good grasp of camera arcane facts, remeber the Thorium based lenses from Pentax in the 60s and 70s, Where the name Super Takumar came from. They have all yellowed years ago. Tom >> Two main factors result in aging (weakening, hazing and yellowing) of >> polycarbonate lens material. [quoted text clipped - 21 lines] > > Tom Holy cow!!! Thorium, how much radioactivity do they give off??? Anything like the old Coleman mantles? Those things 'light up' a Geiger counter... One search said he would recommend handling with cotton gloves to protect from the alpha particles........... > >> Two main factors result in aging (weakening, hazing and yellowing) of > >> polycarbonate lens material. [quoted text clipped - 26 lines] > counter... One search said he would recommend handling with cotton > gloves to protect from the alpha particles........... Read the story about the kid in the U.S. who processed thousands of mantles and nearly created his own mini-reactor. Radiation was detected (once they found out he had it in an old garden shed) a block away. The Brits did a documentary about it. "Wolfgang Schmittenhammer" <tonguesten@sbcglobal.net> wrote in message news:TGDch.9617 > Holy cow!!! Thorium, how much radioactivity do they give off??? Anything > like the old Coleman mantles? Those things 'light up' a Geiger counter... > One search said he would recommend handling with cotton gloves to protect > from the alpha particles........... As I understand it, if the rear lens element were to be put on top of an unexposed film sheet and allowed to sit for some time, there would be noticeable fogging on the film when it was developed. But the camera body itself would prevent the radioactivity from affecting humans merely from having the camera and lens hang from a neckstrap. Just don't peer through the lens by putting it up against your eye, especially with the rear element positioned very close to the eye. > > Two main factors result in aging (weakening, hazing and yellowing) of > > polycarbonate lens material. [quoted text clipped - 21 lines] > > Tom Much like old instrument panel meters painted with radium. But not nearly as harmful. Take a look at some of the Russian binoculars from the 1970s too. Yellow was used as a "haze filter" when imaging distant objects. >> Two main factors result in aging (weakening, hazing and yellowing) of >> polycarbonate lens material. >> 1. UV light exposure. 2. Mechanical stress (internal or external). >> With new camera lenses, particularly inexpensive "kit" lenses utilizing >> plastics in standalone or hybrid lens designs, the vulnerability of the >> plastic should be kept in mind. [snip] >Hey Rich, you have a good grasp of camera arcane facts, remeber the >Thorium based lenses from Pentax in the 60s and 70s, Where the name >Super Takumar came from. They have all yellowed years ago. > >Tom Yeah, but that wasn't due to UV exposure like a polycarbonate lens. It was due to radioactive decay, and that sort of yellowing is okay because thorium is a metal. Besides, they are still better than the crap "kit" lens from Canon. Or something along those lines.... TR "Tom Ross" <TRoss-usenet@columbus.rr.com> wrote in message > > Yeah, but that wasn't due to UV exposure like a polycarbonate lens. It > was due to radioactive decay, and that sort of yellowing is okay > because thorium is a metal. Besides, they are still better than the > crap "kit" lens from Canon. Or something along those lines.... I have 6 SMC Takumar 50mm f/1.4 lenses and they have all exhibited some degree of yellowing. The most severe specimen exhibited, not yellow, but a brownish cast. They were great lenses, but were not of much use for color work, and even if used for B&W I suspected that the color cast probably reduced the amount of light passing through to less than the f/1.8 55mm or f/2.0 55mm versions, neither of which had Thorium and thus no discoloration. About a month ago I decided to return to those classic 50mm f/1.4 lenses, and I wrapped one in aluminum foil, pointed the rear element out a window and let it sit. I checked about 10 days ago and found that the color cast had been significantly lessened. So I put 2 additional 50mm f/1,4 lenses on the windowsill and they, too are exhibiting a much reduced color cast after a week and a half. I may just let those lenses sit out in the sun for a full 60 days, but I anticipate that they will return to their original water-clear condition. The process may be taking more time than normal because the Northeast US is experiencing shorter days than would be present during the summer months, and also because the rear elements are separated from the sunlight by 2 layers of window glass, and part of the UV light is probably being absorbed by the window. I can wait. I had known about this sub-bleaching technique for a number of years, but I had always procrastinated to try it. It turns out that the process is quite straightforward and does, in fact, get rid of the yellow color cast quite nicely. I look forward to using those fast normal lenses once again. I had been using the SMC Takumar 55mm f/1.8, and also the SMC Pentax A 50mm f/1.7, but the classic 50mm f/1.4 SMC Takumar imparted a "glow" to skin tones, especially faces, and it imparted a unique 3-d-like quality especially when used with Kodachrome. I still have one more 50mm f.1.4 lens that I have not subjected to bleaching. I'll do a side-by-side comparison with the bleached lenses when they're done, to see just how effective the bleaching actually was. But I can see a significant change for the better already in lenses that I previously thought had become dogs. The only negative aspect of this process is that it takes a long time and does require some degree of patience. But it looks as though the results will be worth the wait. [] > About a month ago I decided to return to those classic 50mm f/1.4 > lenses, and I wrapped one in aluminum foil, pointed the rear element > out a window and let it sit. I checked about 10 days ago and found > that the color cast had been significantly lessened. So I put 2 > additional 50mm f/1,4 lenses on the windowsill and they, too are > exhibiting a much reduced color cast after a week and a half. Did I miss the smiley? David On Mon, 04 Dec 2006 08:49:47 GMT, "David J Taylor" <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote: >[] >> About a month ago I decided to return to those classic 50mm f/1.4 [quoted text clipped - 5 lines] > >Did I miss the smiley? Why? The method works, I've used it successfully on an old Pentax S-M-C Takumar 50/1.4 that had yellowed over the years. It didn't end up perfect but it was much improved.  SignatureJohn Bean > On Mon, 04 Dec 2006 08:49:47 GMT, "David J Taylor" > <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> [quoted text clipped - 13 lines] > Pentax S-M-C Takumar 50/1.4 that had yellowed over the > years. It didn't end up perfect but it was much improved. OK. What's the mechanism? David "David J Taylor" <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote: >> On Mon, 04 Dec 2006 08:49:47 GMT, "David J Taylor" >> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> [quoted text clipped - 15 lines] > >OK. What's the mechanism? Ultra violet light. > "David J Taylor" > <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote: [quoted text clipped - 21 lines] > > Ultra violet light. But Jeremy said he wrapped the lenses in aluminium foil, which would not pass UV. Or if the read element is exposed, how does adding more UV to a lens cure the damage done by UV in the first place? I know that UV can degrade certain plastics... David >>"David J Taylor" >><david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote: [quoted text clipped - 23 lines] > > I know that UV can degrade certain plastics... I think these are old glass lenses with radioactive elements and the foil is probably just on the back side. >>> "David J Taylor" >>> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote: [quoted text clipped - 26 lines] > I think these are old glass lenses with radioactive elements and the > foil is probably just on the back side. Thanks. Can't really comment. I sold off all my off 35mm stuff a few years back, but I'd never seen any discolouration of the lenses. David "David J Taylor": > Thanks. Can't really comment. I sold off all my off 35mm stuff a > few years back, but I'd never seen any discolouration of the lenses. Thorium lenses were rare and expensive. The most common one was a very fast (for the time) 50mm f/1.4 Super Takumar (but the even more common 50mm f/1.4 SMC Takumar contained no Thorium element and shows no discolouration). I think there was also at least an Yashinon 50mm f/1.4 and several early Leica Summicrons that contained Thorium. Thorium is radioactive and dangerous. While these lenses does not pose a health hazard as long as they are intact (but don't keep such a lens in your pocket or have it sitting on the table next to your bed!) - they can become dangerous if you break them and glass dust from the broken thorium oxide element enter your system, or if they are disposed off in a mannener than cause fragments of the glass to enter the ecosystem. I think maing such lenses became illegal in the mid-1960ies, but some samples are still around and pop up on eBay. Signature- gisle hannemyr [ gisle{at}hannemyr.no - http://hannemyr.com/photo/ ] ------------------------------------------------------------------------ Sigma SD10, Kodak DCS460, Canon Powershot G5, Olympus 2020Z ------------------------------------------------------------------------ [] > I think maing such lenses became illegal in the mid-1960ies, but some > samples are still around and pop up on eBay. Thanks, Gisle and J.Clarke for the explanations. I was only just starting out with photography around that time, so perhaps helps explain why I'd never heard of the problem or the cure. You really do learn something every day! Cheers, David > [] >> I think maing such lenses became illegal in the mid-1960ies, but some [quoted text clipped - 5 lines] > > You really do learn something every day! Did I miss the smiley? >"David J Taylor": >> Thanks. Can't really comment. I sold off all my off 35mm stuff a [quoted text clipped - 4 lines] >common 50mm f/1.4 SMC Takumar contained no Thorium element and shows >no discolouration). Also some of the "Super Multi Coated" (not "SMC") Takumars like the one I have suffer from yellowing. As you rightly say the later SMC Takumars didn't have this problem. SignatureJohn Bean > Also some of the "Super Multi Coated" (not "SMC") Takumars > like the one I have suffer from yellowing. As you rightly > say the later SMC Takumars didn't have this problem. The Super-Multi-Coated Takumars were optically identical to the SMC Takumars. The only difference was that Pentax changed the cosmetic design of the Super-Multi-Coated Takumar, which had a fluted metal focusing ring, to a rubberized focusing ring. When the Spotmatic II was introduced, the normal lens was badged Super-Multi-Coated Takumar, and it had the metal focusing ring. When that camera was replaced by the Spotmatic-F (and with the parallel introduction of the ES and it's subsequent replacement, the ES-II) the normal lens had the rubberized focus rings and the shorter "SMC Takumar" name. The optical designs were the same. Both the earlier Super-Multi-Coated Takumars and the SMC Takumars used thorium elements in their 50mm/1.4 focal lengths. I do not know if Pentax discontinued using Thorium when they replaced the M42 lenses with the K-mounts. I think that the K-mount version had no Thorium, but my knowledge of that line of lenses is somewhat limited. > Thorium lenses were rare and expensive. The most common one was a > very fast (for the time) 50mm f/1.4 Super Takumar (but the even more > common 50mm f/1.4 SMC Takumar contained no Thorium element and shows > no discolouration). I think there was also at least an Yashinon > 50mm f/1.4 and several early Leica Summicrons that contained Thorium. The 35mm f/2.0 SMC Takumar is reputed to have a radioactive element, but mine is water-clear and has never showed even a trace of yellowing. There were three SMC Takumar normal lenses, the 50/1.4, the 55/1.8 and the 55/2. Of those, only the 50mm had the thorium, and it was only in the rear element. I do not recall specifically whether the Super-Takumar version (identical except for lack of Super Multi Coating) had a Thorium element, but I tend to think it did not. >>>"David J Taylor" >>><david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote: [quoted text clipped - 26 lines] > I think these are old glass lenses with radioactive elements and the foil > is probably just on the back side. The foil covers all of the lens, except for an opening for the rear element. It is to reflect back the sunlight so it does not overheat the lens barrel and make the lubricants run inside. "David J Taylor": > Tony Polson: >> "David J Taylor" >>>> "David J Taylor" >>>>> jeremy: >>>>>> About a month ago I decided to return to those classic 50mm f/1.4 >>>>>> lenses, and I wrapped one in aluminum foil, pointed the rear [quoted text clipped - 3 lines] >>>>>> they, too are exhibiting a much reduced color cast after a week >>>>>> and a half. >>>>> Did I miss the smiley? >>>> Why? The method works, I've used it successfully on an old >>>> Pentax S-M-C Takumar 50/1.4 that had yellowed over the >>>> years. It didn't end up perfect but it was much improved. >>> OK. What's the mechanism? >> Ultra violet light. > But Jeremy said he wrapped the lenses in aluminium foil, which would > not pass UV. He wrapped the UV around the front end, and pointed the rear out the window towards the sun. The purpose of the aluminium foil is to act as a mirror, so the UV light strikes the thorium oxide glass element from both sides. > Or if the rear element is exposed, > how does adding more UV to a lens cure the damage done by UV in the > first place? The yellowing of thorium oxide glass is /not/ caused by UV, it is caused by radioactive decay intrinsic to this type of glass. Supplying energy in the shape of strong UV radiation reverses the process. > I know that UV can degrade certain plastics... Correct, but thorium oxide glass is not a plastic. It also is well known that UV radiation removes discolouring from thorium oxide glass. Signature- gisle hannemyr [ gisle{at}hannemyr.no - http://hannemyr.com/photo/ ] ------------------------------------------------------------------------ Sigma SD10, Kodak DCS460, Canon Powershot G5, Olympus 2020Z ------------------------------------------------------------------------ "David J Taylor" <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote in message news:R8Wch.11513 > But Jeremy said he wrapped the lenses in aluminium foil, which would not > pass UV. Or if the read element is exposed, how does adding more UV to a > lens cure the damage done by UV in the first place? The technique of leaving the rear element facing the sun does work over time, but the sun's energy is absorbed by the black finish of the lens barrel, and the lens is at risk of heating up. This might cause the internal lubricants to thin and to run, which would damage the internal optical elements. The aluminum foil is to reflect the light back, rather than to let the lens heat up. Another possible benefit of the foil is to cover the FRONT element, and to reflect the light back toward the rear element, hopefully maximizing the UV that passes through the rear element. My understanding is that SMC coatings absorb most UV, so I have my doubts as to whether that is of much benefit. Other than acting as a reflector of light, the aluminum foil does nothing to bleach the rear element. When I first heard of the technique I had my reservations, but it seems to be working just fine. I'm looking forward to my four 50mm normal lenses returning to active duty. It is taking a long time, but it took 30 years for them to yellow. If it takes 60 or even 90 days to bleach, I have no basis to complain. >> On Mon, 04 Dec 2006 08:49:47 GMT, "David J Taylor" >> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> [quoted text clipped - 15 lines] > > OK. What's the mechanism? If you google "Takumar Yellowing" you'll find numerous references to the phenomenon and to its cure by exposure to UV. The notion that it is somehow caused by the radiation from thorium in the lens however seems to be speculation--there's no mention that I could find of the mechanism by which this yellowing occurs or that by which exposure to UV reverses it--it could be a purely chemical reaction rather than anything related to radiation and the thorium might be totally uninvolved. > David > The notion that it is somehow caused by the radiation from thorium in the > lens however seems to > be speculation--there's no mention that I could find of the mechanism by > which this yellowing occurs or that by which exposure to UV reverses > it--it could be a purely chemical reaction rather than anything related > to radiation and the thorium might be totally uninvolved. This is the first time that I've seen anyone question the cause of the yellowing. The only difference between those lenses that yellowed and those that did not was the presence of Thorium in the optical glass. Everything I have read has attributed the yellowing to the slow breaking-down of the radioactive element. I presume that I may have to bleach the lenses again in the future, as the yellowing may return over time. >> The notion that it is somehow caused by the radiation from thorium in >> the lens however seems to [quoted text clipped - 5 lines] > This is the first time that I've seen anyone question the cause of the > yellowing. I've never seen anybody describe the cause in any terms other than speculative. > The only difference between those lenses that yellowed and those that > did not was the presence of Thorium in the optical glass. And thorium compounds are chemically different from silicon compounds and aluminum compounds and so on. > Everything I have read has attributed the yellowing to the slow > breaking-down of the radioactive element. I presume that I may have to > bleach the lenses again in the future, as the yellowing may return over > time. In 40 years, about 0.0000002857 percent of the thorium will have decayed by alpha emission. whether that is a high enough radiation exposure to cause yellowing I don't know. On the other hand, if you google "glass radiation browning" you'll find quite a lot on the phenomenon, including information that exposure to light often reverses the process over time. I suspect that with enough research you could find tables giving degree of browning vs exposure. The most relevant single article I could find was <http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html> in which an astrophysicist with access to a properly equipped lab took a look at the Kodak Aero-Ektar, which also uses thorium glass. He attributes the discoloration to radiation browning, but never made an attempt to prove or disprove this. Incidentally googling "thorium glass" and the names of various camera manufacturers reveals that it was used by just about everybody at one time or another in one lens or another. In some cases the lenses apparently came from the factory with a yellow cast. > >> Two main factors result in aging (weakening, hazing and yellowing) of > >> polycarbonate lens material. [quoted text clipped - 15 lines] > because thorium is a metal. Besides, they are still better than the > crap "kit" lens from Canon. Or something along those lines.... Read this. http://www.hubbell-canada.com/whitePapers/lighting/whitehlpolylenses.asp >> >> Two main factors result in aging (weakening, hazing and yellowing) of >> >> polycarbonate lens material. [quoted text clipped - 19 lines] > >http://www.hubbell-canada.com/whitePapers/lighting/whitehlpolylenses.asp You really are an idiot. This white paper is describing the characteristics of luminaire lenses. Do you know what a luminaire lens is and the function it serves, and how it has nothing do to with camera lenses? You obviously didn't take the time to read the white paper; otherwise you might've noticed it listed the many advantages plastic lenses have over glass lenses. Here are a few quotes to digest.... "Their advantages over glass are many, including impact resistance, weight and viscosity of flow characteristics that allow them to be injection molded into optical designs of extremely high precision." " Both acrylic and polycarbonate are excellent choices for lens material as they have high transmissivity ratings and show very little hazing." "The use of a UV inhibitor in polycarbonate formulation reduces yellowing significantly." TR > >> >> Two main factors result in aging (weakening, hazing and yellowing) of > >> >> polycarbonate lens material. [quoted text clipped - 41 lines] > "The use of a UV inhibitor in polycarbonate formulation reduces > yellowing significantly." So the article has nothing to do with plastic "camera" lenses (as if lenses somehow magically differ from application to application) and yet you cite advantages of plastic lenses anyway? Which is it? >> >Read this. >> > [quoted text clipped - 24 lines] >So the article has nothing to do with plastic "camera" lenses (as if >lenses somehow magically differ from application to application) and A "luminaire" is a light fixture, and many have a lens. This lens can serve many purposes, and the application most definitely differs from that of camera lenses. Some of the fuctions these lenses serve include protecting the bulb, focusing or diffusing the light, and absorbing UV or IR wavelengths. It ain't magic. It may be beyond your comprehension, but it ain't magic. >yet you cite advantages of plastic lenses anyway? Which is it? Don't throw your strawman at me. You're the one who finds fault with plastic, and you're the one who served up this totally inapplicable white paper to support your foolish notion that polycarbonate is an unsuitable material for camera lens. *I* have no problem with using plastics where it is appropriate and feasible. I have no problem with polycarbonate camera or camera lenses with polycarbonate components ... including lens elements. TR > *I* have no problem with using plastics where it is appropriate and > feasible. I have no problem with polycarbonate camera or camera lenses > with polycarbonate components ... including lens elements. I was just reading that the spectacular Nikon 17-35mm f/2.8 has plastic aspherical elements. It's impractical these days to hand craft glass aspherics. And it seems to work spectacularly well. This is not a cheap lens. >> *I* have no problem with using plastics where it is appropriate and >> feasible. I have no problem with polycarbonate camera or camera lenses [quoted text clipped - 4 lines] > aspherics. And it seems to work spectacularly well. This is not a cheap > lens. I've got one of the earliest hybrid glass-plastic aspheric lenses made (in fact the first commercial camera lens made using this method), the Minolta 35-70mm f4 AF of 1985. At 20+ years old it shows no signs of deterioriation or colour change. The plastic hybrid is internal, not an external surface, and well protected. David > I was just reading that the spectacular Nikon 17-35mm f/2.8 has plastic > aspherical elements. It's impractical these days to hand craft glass > aspherics. And it seems to work spectacularly well. This is not a cheap > lens. Why "impractical?" Perhaps to keep the cost down and the profit margin high? >> I was just reading that the spectacular Nikon 17-35mm f/2.8 has plastic >> aspherical elements. It's impractical these days to hand craft glass [quoted text clipped - 3 lines] > Why "impractical?" Perhaps to keep the cost down and the profit margin > high? Impractical because the price would be so high that nobody would buy them except a few pros with special needs. You do understand the notion of "handcraft", as in you have a room full of Japanese or German guys rubbing pieces of glass together and periodically checkign the curvature until they have it exactly right? I've seen estimates of 60 hours just to start with a spherical surface and adjust it to a parabola--do both sides and that's 120 hours of labor--at $20 an hour (low for someone with that level of skill) that's $2400 in labor alone for one lens element. Many modern lenses have multiple aspherics. So say there are two of them--that's $4800 in labor for the two elements. Put G&A (you understand "G&A"--that's what covers the lights and the heat and the water and the property tax and the mortgage on the building and the secretaries and accountants and managers and security guards and the rest) on top of that at typical levels and you're up to $7200 or more before the lenses are even put in a mount--we're basically talking a $20K lens here. That's why handcrafted aspherics are impractical. And the've been trying ever since aspheric lenses were first discovered to come up with a machine that will figure them properly, with as far as I can tell no success until precision-molded optics came along. > You do understand the notion of "handcraft", as in you have a room full of > Japanese or German guys rubbing pieces of glass together and periodically > checkign the curvature until they have it exactly right? Have you ever heard of computer-controlled lens grinding? It is no longer necessary to have that kind of work done by hand. >> You do understand the notion of "handcraft", as in you have a room full of >> Japanese or German guys rubbing pieces of glass together and periodically >> checkign the curvature until they have it exactly right? > > Have you ever heard of computer-controlled lens grinding? It is no longer > necessary to have that kind of work done by hand. Yes, I have heard of it. What of it? Do you know of any company that is producing computer controlled lens grinding equipment capable of mass-producing photographic quality aspheric lenses? >>> You do understand the notion of "handcraft", as in you have a room full >>> of [quoted text clipped - 9 lines] > producing computer controlled lens grinding equipment capable of > mass-producing photographic quality aspheric lenses? I know that Leica does a lot of computer-controlled lens grinding, and they claim that the results are even better than grinding by hand. I bought a digital P&S camera a few years ago that had a 9-element, all-glass zoom lens. Three of the surfaces were aspherics. Are you suggesting that manufacturers cannot make all-glass lenses with aspheric surfaces, without the price going through the roof? >>>> You do understand the notion of "handcraft", as in you have a room full >>>> of [quoted text clipped - 12 lines] > I know that Leica does a lot of computer-controlled lens grinding, and they > claim that the results are even better than grinding by hand. Do they claim that their computer controlled lens grinding equipment can produce aspherics of photographic quality? Are you comprehending the word "aspheric"? > I bought a digital P&S camera a few years ago that had a 9-element, > all-glass zoom lens. Three of the surfaces were aspherics. What model was that and on what information do you base the contention that all elements of the lens were glass? > Are you suggesting that manufacturers cannot make all-glass lenses with > aspheric surfaces, without the price going through the roof? Yes. >>>>>You do understand the notion of "handcraft", as in you have a room full >>>>>of [quoted text clipped - 26 lines] >>Are you suggesting that manufacturers cannot make all-glass lenses with >>aspheric surfaces, without the price going through the roof? http://oemagazine.com/fromthemagazine/aug01/beatingthegrind.html "Improved technologies make the manufacture of aspherical optics practical." Although it doesn't seem anyone is actually doing it yet. >You do understand the notion of "handcraft", as in you have a room full of >Japanese or German guys rubbing pieces of glass together and periodically [quoted text clipped - 13 lines] >that will figure them properly, with as far as I can tell no success until >precision-molded optics came along. That is a gross over-exaggeration. Leica lenses are almost entirely hand made. Many of the current range include at least one aspherical surface, and that is always hand polished. Yet even these superlative lenses sell for lower prices than you suggest. Several older Nikon lenses had aspheric services too - yet they were nowhere near as expensive as you claim here. Yes, it is expensive to hand polish aspheric elements. But most, if not all of the grinding is done by machine. Only the final, precise polishing needs to be done by hand. To suggest that machines can only grind a spherical surface is pure fantasy. You could have made a valid point about cost, but by over-exaggerating it beyond all logic, you failed to make the point at all. >>You do understand the notion of "handcraft", as in you have a room full of >>Japanese or German guys rubbing pieces of glass together and periodically [quoted text clipped - 21 lines] > than you suggest. Several older Nikon lenses had aspheric services > too - yet they were nowhere near as expensive as you claim here. What do "older Nikon lenses" made when labor rates in Japan were much lower than they are today have to do with current costs of doing business? As for Leica, how many aspheric surfaces do they have? If it's one then the cost I came up with is in the ballpark. Remember that an "aspheric" lens can have one aspheric surface and one spherical surface. Regardless. how much market do you think there is for Leica-priced single-focal-length lenses? > Yes, it is expensive to hand polish aspheric elements. But most, if not > all of the grinding is done by machine. Only the final, precise > polishing needs to be done by hand. To suggest that machines can only > grind a spherical surface is pure fantasy. Machines can rough-grind, not do the final figuring. > You could have made a valid point about cost, but by over-exaggerating > it beyond all logic, you failed to make the point at all. So show me where I exaggerated. How many hours does it take to grind a single aspheric surface? If I'm wrong on that give me a better number. How about the labor costs? Do German lens grinders get paid less than $20/hr? Or maybe they have less G&A somehow? If you're going to accuse someone who laid out all the numbers of "exaggerating" then at least have the courtesy to show the error in the calculation. >If you're going to accuse someone who laid out all the numbers of >"exaggerating" then at least have the courtesy to show the error in the >calculation. Your first gross error is in asserting that aspheric lenses cannot be ground by a machine, and must be ground by hand. That is patent nonsense, and is completely wrong. Nikon and Leica have been making aspheric lenses for years. They are mechanically ground to an aspheric surface then polished by hand. You then claim that costs of producing aspheric surfaces are astronomic, which is based on your false assumption above. Plenty of mechanically ground and hand polished aspheric elements can be found in lenses that sell for a fraction of the silly prices you suggest. Finally, you accuse me of introducing the question of old Nikkors that were made when wages in Japan were cheap. Yet the lenses I am talking about were made in the 1990s, when Japanese wages were at an all-time high relative to the wages in other developed countries. In relative terms, Japanese wages are cheaper now than they were then. So you are quite wrong again. But please don't let me stop you making outrageous statements that have absolutely no basis in fact. It makes hilarious reading, and I thank you for brightening up an otherwise dull newsgroup with your ridiculous and baseless assertions. ;-) >>If you're going to accuse someone who laid out all the numbers of >>"exaggerating" then at least have the courtesy to show the error in the [quoted text clipped - 5 lines] > aspheric lenses for years. They are mechanically ground to an > aspheric surface then polished by hand. Source please. > You then claim that costs of producing aspheric surfaces are > astronomic, which is based on your false assumption above. Plenty of > mechanically ground and hand polished aspheric elements can be found > in lenses that sell for a fraction of the silly prices you suggest. So show me the error in the numbers. > Finally, you accuse me of introducing the question of old Nikkors that > were made when wages in Japan were cheap. Yet the lenses I am talking > about were made in the 1990s, when Japanese wages were at an all-time > high relative to the wages in other developed countries. In relative > terms, Japanese wages are cheaper now than they were then. So you are > quite wrong again. Now in the 1990s please state which Nikkor used glass aspheric elements and what the price was and the basis on which you assert that it used glass aspherics and not molded aspherics. > But please don't let me stop you making outrageous statements that have > absolutely no basis in fact. It makes hilarious reading, and I thank > you for brightening up an otherwise dull newsgroup with your ridiculous > and baseless assertions. I see, you're just abusive for the Hell of it. <plonk> Signature--John to email, dial "usenet" and validate (was jclarke at eye bee em dot net) >>>If you're going to accuse someone who laid out all the numbers of >>>"exaggerating" then at least have the courtesy to show the error in the [quoted text clipped - 26 lines] > and what the price was and the basis on which you assert that it used > glass aspherics and not molded aspherics. We were just discussing the 20-35/2.8 glass aspheric versus the plastic 17-35. >>But please don't let me stop you making outrageous statements that have >>absolutely no basis in fact. It makes hilarious reading, and I thank [quoted text clipped - 4 lines] > > <plonk> >>>>If you're going to accuse someone who laid out all the numbers of >>>>"exaggerating" then at least have the courtesy to show the error in the [quoted text clipped - 29 lines] > We were just discussing the 20-35/2.8 glass aspheric versus the plastic > 17-35. And what leads you to believe that it had a glass aspheric rather than a molded one? >>>But please don't let me stop you making outrageous statements that have >>>absolutely no basis in fact. It makes hilarious reading, and I thank [quoted text clipped - 4 lines] >> >> <plonk> Signature--John to email, dial "usenet" and validate (was jclarke at eye bee em dot net) >>>Now in the 1990s please state which Nikkor used glass aspheric elements >>>and what the price was and the basis on which you assert that it used [quoted text clipped - 5 lines] > And what leads you to believe that it had a glass aspheric rather than a > molded one? Hmm, I can't confirm that but I found mention of a comparable Tokina: <http://www.fredmiranda.com/reviews/showproduct.php?product=234&sort=7&cat=40&page=1> "Two Pioneering all-glass aspherical lens elements, one front and rear" >>>>Now in the 1990s please state which Nikkor used glass aspheric elements >>>>and what the price was and the basis on which you assert that it used [quoted text clipped - 9 lines] ><http://www.fredmiranda.com/reviews/showproduct.php?product=234&sort=7&cat=40&page=1> >"Two Pioneering all-glass aspherical lens elements, one front and rear" Paul, you are right. The 20-35mm f/2.8 AF Nikkor had a glass aspherical element. <j.clarke> Source? SOURCE???? WHAT IS YOUR SOURCE??????? </j.clarke> >>>>Now in the 1990s please state which Nikkor used glass aspheric elements >>>>and what the price was and the basis on which you assert that it used [quoted text clipped - 9 lines] > <http://www.fredmiranda.com/reviews/showproduct.php?product=234&sort=7&cat=40&page=1> > "Two Pioneering all-glass aspherical lens elements, one front and rear" Read that carefully--note that they refer to those elements being made by Hoya's precision molding technique. It was my understanding that molded aspherics could only be made in plastic, not glass. If in fact precision molded glass aspherics are in commercial production then the whole lot of us are damned fools for not plonking a RichA thread when we first saw it. Signature--John to email, dial "usenet" and validate (was jclarke at eye bee em dot net) >It was my understanding that molded >aspherics could only be made in plastic, not glass. Even Cosina used moulded glass aspherics years before they first used plastic. Leica ASPH lenses are hand-finished but the blanks are press-moulded rather than ground to shape. SignatureJohn Bean > then the whole lot of > us are damned fools for not plonking a RichA thread when we first saw it. I think just plonking RichA should be enough. He's not going to change and if the information is real, someone else will post it, too. >> Hmm, I can't confirm that but I found mention of a comparable Tokina: >> <http://www.fredmiranda.com/reviews/showproduct.php?product=234&sort=7&cat=40&page=1> [quoted text clipped - 4 lines] >aspherics could only be made in plastic, not glass. If in fact precision >molded glass aspherics are in commercial production[...] Which they are. Canon have been mass-producing molded aspheric elements in both glass & plastic for decades: <http://www.canon.com/camera-museum/tech/room/b_hikyu.html> --------- Aspherical lens elements have a special non-spherical surface to converge central and peripheral light rays at a single focal point perfectly. The FD55mm f/1.2 AL was marketed in 1971 as the first interchangeable lens for 35mm SLR camera in the world, employing an aspherical lens element. Canon uses four different type of aspherical lens elements now depending on the purpose; 1. a ground and polished glass aspherical lens element. 2. a molded glass aspherical lens element. 3. a molded plastic aspherical lens element produced by a high-precision molding technology. 4. a replica aspherical lens element, ultraviolet-light-hardening resin layer on a spherical glass lens element. Large diameter ground and polished aspherical lens elements are used for "L" series lenses to achieve sharp definition. --------- [...] then the whole lot of >us are damned fools for not plonking a RichA thread when we first saw it. Well, yeah. ;) >>>> Now in the 1990s please state which Nikkor used glass aspheric elements >>>> and what the price was and the basis on which you assert that it used [quoted text clipped - 10 lines] > > "Two Pioneering all-glass aspherical lens elements, one front and rear" Hmm, not ground though but molded: "Hoya Corporation, the world’s largest optical glass manufacturer, has created a micron-tuned precision molding technique with the accuracy to form aspherical surfaces to the thousandths of a millimeter." >>>>> Now in the 1990s please state which Nikkor used glass aspheric >>>>> elements [quoted text clipped - 17 lines] > created a micron-tuned precision molding technique with the accuracy to > form aspherical surfaces to the thousandths of a millimeter." And Sigma use nothing except moulded glass aspherics. Tamron use hybrid glass-plastic. Minolta use(d) both and also used pure plastic aspherics, notably in their series of Riva zoom compact cameras which managed to have a 3X zoom constructed of only four elements, using two aspherical elements. David >Source please. You make me laugh! You spout complete and utter bullshit, without ever quoting any sources for your nonsense, and then you ask *me* for a source! You are truly priceless! >Now in the 1990s please state which Nikkor used glass aspheric elements You could easily find this information for yourself. The reason you haven't is that it shows your ridiculous assertions to be completely without foundation. Nikon lenses manufactured in the 1990s with precision ground aspheric elements included the 58mm f/1.2 NOCT-Nikkor (deleted 1997), the 20-35mm f/2.8 AF(-D) Nikkor, which has already been discussed, and the 28mm f/1.4 AF-D Nikkor. All have at least one aspheric surface that is machine ground. None of these were cheap lenses, but they were not remotely as expensive as you would like people here to believe. >> *I* have no problem with using plastics where it is appropriate and >> feasible. I have no problem with polycarbonate camera or camera lenses >> with polycarbonate components ... including lens elements. >I was just reading that the spectacular Nikon 17-35mm f/2.8 has plastic >aspherical elements. It's impractical these days to hand craft glass >aspherics. And it seems to work spectacularly well. This is not a cheap >lens. But it does raise an interesting question. Those plastic aspherics are expensive, but not nearly as expensive as glass ones. Might we expect to see some price drops? Signature--- Paul J. Gans > Hey Rich, you have a good grasp of camera arcane facts, remeber the > Thorium based lenses from Pentax in the 60s and 70s, Where the name > Super Takumar came from. They have all yellowed years ago. My Super Takumars are still in great shape. But you're right on one count - RichA is an idiot. > > Hey Rich, you have a good grasp of camera arcane facts, remeber the > > Thorium based lenses from Pentax in the 60s and 70s, Where the name > > Super Takumar came from. They have all yellowed years ago. > > My Super Takumars are still in great shape. But you're right on one > count - RichA is an idiot. Because the radiation doesn't yellow the glass, it's yellowish to BEGIN with. If you've go a few thousand years, it might do something to it though. I've been in a mine where the quartz (normally clear had turned black due to radiation from local uranium sources, but the strength of those sources was very high and the time frame was eons. >Two main factors result in aging (weakening, hazing and yellowing) of >polycarbonate lens material. >1. UV light exposure. Only an issue if the front element is the plastic one, as glass filters out UV. Haze filters also filter out UV. Besides which, very few of us in this newsgroup would be using lenses with plastic elements in the first place - they're generally found in extremely cheap consumer cameras, not in DSLR lenses. [] > Only an issue if the front element is the plastic one, as glass > filters out UV. Haze filters also filter out UV. > Besides which, very few of us in this newsgroup would be using lenses > with plastic elements in the first place - they're generally found in > extremely cheap consumer cameras, not in DSLR lenses. I believe I use plastic element lenses rather a lot - my glasses are made from them! Comfortably light, seem to be reliable, don't scratch easily in normal use, and I don't see any noticeable evidence of colouring after a few years use. Oh, and more expensive than glass, IIRC. David |
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