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#21
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Quote:
https://www-photoinfos-com.translate..._x_tr_pto=wapp Terry S |
#22
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Quote:
<<The image quality of all three lenses improves by stopping down slightly to f/5.6 or 8. After that, the resolution decreases due to diffraction effects at the aperture.>> |
#23
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So again, the optical physic could help us.
As far as I know, all optical formulas are reversible. A given ratio of let's say 5:1 could be changed to 1:5 . Decades ago macro lenses have been rare and very expensive. It has been usual to grap a 50mm lens and to bring it in retro position to the camera, just to maintain the qualities of the lens while making sharp macros. A longer lens of 100m would have been better because the greater distance to the biting subject but 100mm lenses hasn't been as sharp as the shorter 50mm, so 50mm have been a good choice. Landscape at infinity will give a small projection onto the small negative , but photographing bees will give tiny subjects the doubled size. That's not what a landscape lens is designed for. Retro turning the lenses then is necessary because most of our lenses aren't designed symmetrically - the front group often has another design then the rear group. Now the lens is able to produce sharp images of tiny and enlarged things. A symmetrical lens must not to be turned for projection or photographing, because nothing would change then. On the other hand my enlarging machine has been designed as an enlarger of course. But with some further equipment it was possible to use the enlarger as a repro camera. Retro positioning the lens is not necessary because in each case, enlarging or projectioning, the direction of the ratios remains the same and we don't leave the ideal conditions of the lens. The man has told us about the minimizing ratio of 2:1 in its construction . Enlarging / magnifying 1:2 with enlarging lenses is "allowed", viceversa too. So I only could see issues with the digital camera but probably not with optical principles. <<After that, the resolution decreases due to diffraction effects at the aperture.>> That is what I would expect with enlarging lenses and to me it seems to be logical with the lens design in mind. But again I don't believe in diffraction with a relatively wide open lens. I am neither a scientist nor a lens designer but to me the results of the tests tell more about the lens design, it's requirements and their realization than about diffraction. But if diffraction or simply the restrictions from the lens design - the answer to Nat should be yes, stopping down your lens could be detrimental. It could depend on your magnification ratio if the problems will rise or not. Last edited by Reginald S; 28th May 2022 at 01:19 AM. |
#24
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Macro
Before Macro lenses were within my financial pocket and I was still using fully manual cameras, or those with only aperture priority automation I had a set of bellows that fitted my camera (Pentax M42 with an adapter for Minolta MC/MD) I used a 105mm F4.5 TTH Ental Enlarging lens that stopped down to F32.
I knew nowt about diffraction in those days and frequently stopped it down fully to get the extra depth of field especially at larger magnifications than 1-1 and was quite happy with the sharp prints that resulted when printed up to 10x12. (I rarely printed larger in those days). Grain was more of a problem. I fully believe that some of the associated problems that are supposed to happen when you treat lenses to the level/purpose they 'were not designed for', are mostly an urban myth. Chinese Whispers reign here! I am not saying that they do not happen, but for the level we use lenses for, these aberrations are insignificant for our purposes. To appreciate what they are, I suggest can only clearly be seen in a meaningful way in controlled laboratory conditions. Much the same applies to the film - is film 'A' made by 'Ilfdak' sharper than the alternative film 'B' made by 'Kodford'.? Most film today may well out perform lenses, especially if the cameras are not on on a firm tripod. These observations are of course, my opinion, so not claiming they are 100% accurate, it is just what I found over the years. Last edited by John King; 28th May 2022 at 07:20 AM. |
#25
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So why not stop whispering and changing opinions then?
I am in the uncomfortable but somehow beneficial situation to reanimate my darkroom which will need combining some tests like fiddling from N-3 to N+2 with new to me Tanol developer, aligning the enlarger and finding the lens best performing under new LED light while enlarging large magnifications. Meanwhile I will quit whispering here :-) |
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