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#1
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For the cost of today's lenses, should they be diffraction-limited, wide open?
$1800 for an 85mm f1.4 from Nikon. That's about 2x what the old one cost.
Is the lens $1000 better or should it be as good at f/1.4 as f/4? I'm not sure. I know that some optics made as f/4.0 have been diffraction limited. Pentax had some, but they weren't camera lenses. Some have claimed certain telephotos in the pro bracket have been diffraction-limited at f/2.8, but I've never seen it demonstrated. So, the question is, is it possible to make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what price? Likely it is, but they haven't done it. |
#2
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For the cost of today's lenses, should they be diffraction-limited,wide open?
On 8/11/2012 1:48 p.m., Anthony Polson wrote:
Rich wrote: $1800 for an 85mm f1.4 from Nikon. That's about 2x what the old one cost. Is the lens $1000 better or should it be as good at f/1.4 as f/4? I'm not sure. I know that some optics made as f/4.0 have been diffraction limited. Pentax had some, but they weren't camera lenses. Some have claimed certain telephotos in the pro bracket have been diffraction-limited at f/2.8, but I've never seen it demonstrated. So, the question is, is it possible to make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what price? Likely it is, but they haven't done it. It might be better if, instead of using the term "diffraction limited", you described your requirement as "a lens that gives its sharpest results when wide open". That is what you mean after all. Only Leica makes lenses that do that, and Leica lens prices are self-evidently very high indeed. Ridiculously high, even for Leica users. Which Leica lenses? http://www.photozone.de/canon-eos/20...report?start=1 Summilux R 50mm f1.4 is pretty good, but peaks at f5.6 here, much the same as any of the ( /much/ cheaper) 50mm lenses. I'm considering replacing two of my Leica lenses in the next year before signs of wear mean their used values begin to fall. I'm looking hard at Carl Zeiss ZM and Voigtländer lenses, both made in Japan by Cosina and costing a fraction of Leica prices. However, they don't perform at their best wide open. |
#3
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For the cost of today's lenses, should they be diffraction-limited,wide open?
On 08/11/2012 00:27, Rich wrote:
$1800 for an 85mm f1.4 from Nikon. That's about 2x what the old one cost. Is the lens $1000 better or should it be as good at f/1.4 as f/4? I'm not sure. I know that some optics made as f/4.0 have been diffraction limited. Pentax had some, but they weren't camera lenses. Some have claimed certain telephotos in the pro bracket have been diffraction-limited at f/2.8, but I've never seen it demonstrated. So, the question is, is it possible to make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what price? Likely it is, but they haven't done it. f1.6 and full achromatic mirror telescope has been done by Cambridge University. http://www.ast.cam.ac.uk/about/three-mirror.telescope 20" aperture prototype was built. That is one of the fastest diffraction limited wide field instruments I know of. You are hampered in real cameras by simultaneously wanting diffraction limited and a flat film plane when the lens is fast and the small angle approximations no longer hold. There is always a trade off. Anything can be done in principle but the cost to manufacture it and difficulties in assembly make it prohibitive. You could get the on axis sharpness truly diffraction limited by sacrificing edge resolution but never all at the same time and a flat film plane. Something has to give. At around f4 or f5 things are a lot easier. Most real lenses tend to have their resolution sweet spot at about that working aperture. -- Regards, Martin Brown |
#4
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For the cost of today's lenses, should they be diffraction-limited,wide open?
On 08/11/2012 00:48, Anthony Polson wrote:
(...) "a lens that gives its sharpest results when wide open". Only Leica makes lenses that do that, That's a ridiculous claim. http://www.cookeoptics.co.uk/ and http://lenses.zeiss.com/camera-lenses/carl-zeiss-camera-lenses/cine_lenses.html would be 2 examples of lens manufacturers other than Leica that are sharp wide open. And I have a hunch that these qualify as well: http://www.canon.co.uk/For_Home/Product_Finder/Digital_Cinema/Cine_Lenses/ http://www.fujifilm.com/products/optical_devices/cine/ -- audentes fortuna iuvat |
#5
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For the cost of today's lenses, should they be diffraction-limited,wide open?
On 08/11/2012 16:53, Anthony Polson wrote:
Joe Kotroczo wrote: On 08/11/2012 00:48, Anthony Polson wrote: (...) "a lens that gives its sharpest results when wide open". Only Leica makes lenses that do that, That's a ridiculous claim. http://www.cookeoptics.co.uk/ and http://lenses.zeiss.com/camera-lenses/carl-zeiss-camera-lenses/cine_lenses.html would be 2 examples of lens manufacturers other than Leica that are sharp wide open. And I have a hunch that these qualify as well: http://www.canon.co.uk/For_Home/Product_Finder/Digital_Cinema/Cine_Lenses/ http://www.fujifilm.com/products/optical_devices/cine/ With respect, I believe you have missed the point here. First, I was talking about still photography, not cine. I have no interest in, or specialist knowledge of, the latter. Neither is it on-topic for this newsgroup. A lens is a lens. Nothing stops you from taking stills with a cine lens. Second, I was not talking about lenses that are merely *sharp* wide open but lenses that give *their sharpest results* when used wide open. There is a difference. So was I. Cine lenses must be of equal sharpness along the full range of stops, so they should be equally sharp wide open as they are stopped down. In fact, shouldn't a lens that is less sharp stopped down than it is fully open be considered defective? Perhaps, given the confusion I appear to have caused, I should have stayed with Rich's term "diffraction limited". ;-) There is a difference between "diffraction limited" and "sharpest at full aperture" too... A lens that is sharpest at full aperture is not necessarily diffraction limited. -- audentes fortuna iuvat |
#6
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For the cost of today's lenses, should they be diffraction-limited,wide open?
On 08/11/2012 23:32, RichA wrote:
On Nov 8, 12:24 pm, Joe Kotroczo wrote: On 08/11/2012 16:53, Anthony Polson wrote: Joe Kotroczo wrote: On 08/11/2012 00:48, Anthony Polson wrote: (...) "a lens that gives its sharpest results when wide open". Only Leica makes lenses that do that, That's a ridiculous claim. http://www.cookeoptics.co.uk/ and http://lenses.zeiss.com/camera-lenses/carl-zeiss-camera-lenses/cine_l... would be 2 examples of lens manufacturers other than Leica that are sharp wide open. And I have a hunch that these qualify as well: http://www.canon.co.uk/For_Home/Product_Finder/Digital_Cinema/Cine_Le... http://www.fujifilm.com/products/optical_devices/cine/ With respect, I believe you have missed the point here. First, I was talking about still photography, not cine. I have no interest in, or specialist knowledge of, the latter. Neither is it on-topic for this newsgroup. A lens is a lens. Nothing stops you from taking stills with a cine lens. Second, I was not talking about lenses that are merely *sharp* wide open but lenses that give *their sharpest results* when used wide open. There is a difference. So was I. Cine lenses must be of equal sharpness along the full range of stops, so they should be equally sharp wide open as they are stopped down. In fact, shouldn't a lens that is less sharp stopped down than it is fully open be considered defective? Perhaps, given the confusion I appear to have caused, I should have stayed with Rich's term "diffraction limited". ;-) There is a difference between "diffraction limited" and "sharpest at full aperture" too... A lens that is sharpest at full aperture is not necessarily diffraction limited. What difference? What would cause a lens wide open and diffraction limited (across the visual spectrum) to not be sharpest when wide open? Resolution laws would argue otherwise. But you can still make a lens that is at its sharpest when wide open but whose sharpness is not significantly improved by stopping down. Such lenses are usually designed to avoid vignetting at the corners of the field of view. They are not diffraction limited at full aperture but they hold their sharpness at some particular nominal diameter. -- Regards, Martin Brown |
#7
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For the cost of today's lenses, should they be diffraction-limited,wide open?
On 08/11/2012 23:32, RichA wrote:
(...) There is a difference between "diffraction limited" and "sharpest at full aperture" too... A lens that is sharpest at full aperture is not necessarily diffraction limited. What difference? What would cause a lens wide open and diffraction limited (across the visual spectrum) to not be sharpest when wide open? Resolution laws would argue otherwise. Who says that a lens has to reach it's diffraction limit wide open? Can it not be diffraction limited at f/11 or something, and less sharp at any other stop, smaller or larger? And who says that a lens which is sharpest wide open has also reached it's diffraction limit? Can it not be sharpest wide open, but still a long way off it's diffraction limit? After all, what "diffraction limited" really means is "reaching it's theoretical maximum resolution". -- audentes fortuna iuvat |
#8
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For the cost of today's lenses, should they be diffraction-limited, wide open?
Joe Kotroczo wrote:
On 08/11/2012 23:32, RichA wrote: There is a difference between "diffraction limited" and "sharpest at full aperture" too... A lens that is sharpest at full aperture is not necessarily diffraction limited. What difference? What would cause a lens wide open and diffraction limited (across the visual spectrum) to not be sharpest when wide open? Resolution laws would argue otherwise. Who says that a lens has to reach it's diffraction limit wide open? Can it not be diffraction limited at f/11 or something, and less sharp at any other stop, smaller or larger? And who says that a lens which is sharpest wide open has also reached it's diffraction limit? Can it not be sharpest wide open, but still a long way off it's diffraction limit? After all, what "diffraction limited" really means is "reaching it's theoretical maximum resolution". And what is meant by "sharpest"? Sharpest in the centre? Sharpest at the edges? Those are often two different apertures. -- Chris Malcolm |
#9
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For the cost of today's lenses, should they be diffraction-limited,wide open?
On 09/11/2012 17:58, Chris Malcolm wrote:
Joe Kotroczo wrote: On 08/11/2012 23:32, RichA wrote: There is a difference between "diffraction limited" and "sharpest at full aperture" too... A lens that is sharpest at full aperture is not necessarily diffraction limited. What difference? What would cause a lens wide open and diffraction limited (across the visual spectrum) to not be sharpest when wide open? Resolution laws would argue otherwise. Who says that a lens has to reach it's diffraction limit wide open? Can it not be diffraction limited at f/11 or something, and less sharp at any other stop, smaller or larger? And who says that a lens which is sharpest wide open has also reached it's diffraction limit? Can it not be sharpest wide open, but still a long way off it's diffraction limit? After all, what "diffraction limited" really means is "reaching it's theoretical maximum resolution". And what is meant by "sharpest"? Sharpest in the centre? Sharpest at the edges? Those are often two different apertures. If you want to pick nits the problem is that to be "sharpest" as a true fully optimised glass based apochromat requires that the red image be truly diffraction limited and the green and blue images be very slightly geometrically degraded. I don't think anybody does this in practice. You end up with slight purple haloes on point sources. resolution is 1.22D/lambda Varies by a factor of two from deep red 680nm to violet 340nm. Astronomical instruments are optimised to diffraction limited for object at infinity and a realisable (not not always flat) focal plane. Camera lenses have to cope with a wider range of object distances. Mostly the marketing dept stick APO on to fleece wannabbees like RichA. The RichA troll just likes to **** and moan. -- Regards, Martin Brown |
#10
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For the cost of today's lenses, should they be diffraction-limited, wide open?
RichA wrote:
On Nov 8, 5:49*am, Martin Brown wrote: On 08/11/2012 00:27, Rich wrote: $1800 for an 85mm f1.4 from Nikon. *That's about 2x what the old one cost. Is the lens $1000 better or should it be as good at f/1.4 as f/4? *I'm not sure. *I know that some optics made as f/4.0 have been diffraction limited. Pentax had some, but they weren't camera lenses. *Some have claimed certain telephotos in the pro bracket have been diffraction-limited at f/2.8, but I've never seen it demonstrated. So, the question is, is it possible to make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what price? *Likely it is, but they haven't done it. f1.6 and full achromatic mirror telescope has been done by Cambridge University. http://www.ast.cam.ac.uk/about/three-mirror.telescope 20" aperture prototype was built. That is one of the fastest diffraction limited wide field instruments I know of. You are hampered in real cameras by simultaneously wanting diffraction limited and a flat film plane when the lens is fast and the small angle approximations no longer hold. There is always a trade off. Anything can be done in principle but the cost to manufacture it and difficulties in assembly make it prohibitive. You could get the on axis sharpness truly diffraction limited by sacrificing edge resolution but never all at the same time and a flat film plane. Something has to give. At around f4 or f5 things are a lot easier. Most real lenses tend to have their resolution sweet spot at about that working aperture. -- Regards, Martin Brown Only problem, with a central obstruction like it has, contrast would suffer. It should be possible with today's lens and mirror making technology to devise a mirror which instead of reflecting straight back, offset the folded beam offset to one side, thus avoiding the need for the obstruction. -- Chris Malcolm |
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