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Photo Forum / Digital Photography / DSLR Cameras / November 2006Plastic lenses losing element aligment?
A magazine made the comment the other day as to whether a plastic-housed lens would maintain alignment over the "long haul." I wasn't aware this was an issue. I'd have thought that expansion and contraction of plastic during temp changes might compromise the shape of glass elements mounted in them though. For instance, if you take lens out on a cold day, the plastic will shrink, possibly pinching or warping glass lens elements. However, how this might effect image quality is another issue. High quality professional (non-consumer camera) lenses usually have "compensating mounts" that can accommodate shape and size changes when aluminum or whatever housing material is exposed to different temperatures. http://www.freepatentsonline.com/5570238.html >A magazine made the comment the other day as to whether a > plastic-housed lens would maintain alignment over the "long haul." A magazine made the comment the other day as to whether you're a troll. And why wouldn't this happen for other materials than plastic. Why are you singling out plastic. ben >A magazine made the comment the other day as to whether a > plastic-housed lens would maintain alignment over the "long haul." I [quoted text clipped - 8 lines] > exposed to different temperatures. > http://www.freepatentsonline.com/5570238.html >And why wouldn't this happen for other materials than plastic. >Why are you singling out plastic. > >ben Plastic, at least some plastics, has a greater coefficient of thermal expansion that metal. but, I'd bet that the lens designers knew that before I did. >>And why wouldn't this happen for other materials than plastic. >>Why are you singling out plastic. [quoted text clipped - 3 lines] >Plastic, at least some plastics, has a greater coefficient of thermal >expansion that metal. Which metal? They are all different hence freezing ball of a brass monkey.  Signature\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ \/\/\/\/\ Chris Hills Staffs England /\/\/\/\/ /\/\/ chris@phaedsys.org www.phaedsys.org \/\/\ \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ > >>And why wouldn't this happen for other materials than plastic. > >>Why are you singling out plastic. [quoted text clipped - 6 lines] > Which metal? They are all different hence freezing ball of a brass > monkey. I doubt there is any metal used in lenses that has a differential of expansion between it and the glass elements that is anywhere near as large as that between plastic and the glass elements. >> >>And why wouldn't this happen for other materials than plastic. >> >>Why are you singling out plastic. [quoted text clipped - 10 lines] > expansion between it and the glass elements that is anywhere near as > large as that between plastic and the glass elements. I doubt there is any plastic used in lenses that has a differential of expansion between it and the glass elements that is anywhere near as large as that between metal and the glass elements. > >> >>And why wouldn't this happen for other materials than plastic. > >> >>Why are you singling out plastic. [quoted text clipped - 14 lines] > expansion between it and the glass elements that is anywhere near as > large as that between metal and the glass elements. Then you'd be wrong. >> I doubt there is any plastic used in lenses that has a differential of >> expansion between it and the glass elements that is anywhere near as >> large as that between metal and the glass elements. > > Then you'd be wrong. Plastic is an umbrella term ... it includes some amazing materials that can outperform metals and metal alloys in given applications. You really need to learn more about this before you make silly statements and post arcane innuendos. > >> I doubt there is any plastic used in lenses that has a differential of > >> expansion between it and the glass elements that is anywhere near as [quoted text clipped - 6 lines] > to learn more about this before you make silly statements and post arcane > innuendos. That is true. Pity all that's used in cameras is boring old polycarbonate and not "high-tech" kevlar, boron, carbon nanotube composites. But don't let that stop you from LOOKING UP the thermal coefficient of expansion of aluminum, magnesium, polycarbonate, FPL glasses, Flint glass, crown glass, etc. Also, look-up "compensation cell" and while you at it, look-up why they use stainless steel for the most critical lens mount applications in industrial optics. > That is true. Pity all that's used in cameras is boring old > polycarbonate and not "high-tech" > kevlar, boron, carbon nanotube composites. And you can prove that? > But don't let that stop you from LOOKING UP the thermal coefficient of > expansion of aluminum, magnesium, polycarbonate, FPL glasses, Flint > glass, crown glass, etc. Also, look-up > "compensation cell" and while you at it, look-up why they use stainless > steel for the most critical lens mount applications in industrial > optics. What does that have to do with this newsgroup? Industrial optics must perform over much wider temperature ranges. Do you want to spend 100000 on a lens? Get real, Rich! >> >> I doubt there is any plastic used in lenses that has a differential of >> >> expansion between it and the glass elements that is anywhere near as [quoted text clipped - 10 lines] >polycarbonate and not "high-tech" >kevlar, boron, carbon nanotube composites. Do you have any evidence to indicate that polycarbonate is the only plastic being used or that it is an inappropriate material? While you're at it, do you have ANY evidence to indicate that a fiber compound like Kevlar would be an appropriate material for camera lenses? Carbon nanotube composites? Why not add ceramic matrix composites to this fantasy? >But don't let that stop you from LOOKING UP the thermal coefficient of >expansion of aluminum, magnesium, polycarbonate, FPL glasses, Flint >glass, crown glass, etc. Also, look-up >"compensation cell" and while you at it, look-up why they use stainless >steel for the most critical lens mount applications in industrial >optics. While you're stuck on LOOKING UP, why don't you look up the name of this froup? That's right - rec.photo.digital.slr-systems. Now, do you really think the high tolerances required in industrial optics has any place here? I do not doubt that differences in thermal expansion the glass elements and the other elements, whether plastic or metal, is a real problem. I seriously doubt it is a significant problem for most photographers. TR > >> >> I doubt there is any plastic used in lenses that has a differential of > >> >> expansion between it and the glass elements that is anywhere near as [quoted text clipped - 31 lines] > you really think the high tolerances required in industrial optics has > any place here? You mean when a lens is expected to accurately transmit unaberrated light rays down on pixels the size of large bacteria, with microlenses in front whose positional tolerances are in the 100,000th of a mm range? Could be! > I do not doubt that differences in thermal expansion the glass > elements and the other elements, whether plastic or metal, is a real > problem. I seriously doubt it is a significant problem for most > photographers. Maybe not. But the high curvatures on elements in more compact lenses with wider zoom ranges being used to day and the use of SD, ED, etc, glass mean greater susceptability to things like misalignment, pinching, etc, than in older lens designs, with shallower curves, and longer focal ratios than are in use now. Plastic, as a mounting medium for lenses is far less thermally stable than aluminum, magnesium or steel. <another baseless anti-plastic post> Rich, all these posts against plastic in cameras actually do is convince people you have a problem. Personally, the level of obsession (and it is an obsession) over plastic in cameras convinces me that you have Asperger's Syndrome. You need to talk to your therapist about this. Really. Austin > <another baseless anti-plastic post> > [quoted text clipped - 3 lines] > have Asperger's Syndrome. You need to talk to your therapist about > this. Really. I hope his therapist takes his keyboard. > <another baseless anti-plastic post> > [quoted text clipped - 5 lines] > > Austin Asperergers is treated with drugs, blue pill for you Mister Anderson <> > > <another baseless anti-plastic post> > > [quoted text clipped - 7 lines] > > Asperergers is treated with drugs, blue pill for you Mister Anderson <> "I hear and obey...the will of Canon..." >> > <another baseless anti-plastic post> >> > [quoted text clipped - 9 lines] > > "I hear and obey...the will of Canon..." LOL? Never had a Canon in my life Richie boy, you are sadly mistook in your Oly shilling assumption. > >> > <another baseless anti-plastic post> > >> > [quoted text clipped - 12 lines] > LOL? Never had a Canon in my life Richie boy, you are sadly mistook in your > Oly shilling assumption. I've never shilled for Olympus. I'll slam any company that F----- up. |
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