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> El Nikkor or El Nikkor N Enlerger lens. |
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#11
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#12
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Quote:
It isn't precise because the fall off for each focal length differs. Remember, the fall is controlled by Cos^4. All lenses are bound by this physical law - so the Cos^4 curve should be quoted in the illumination fall off test results. Martin |
#13
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Neil mentioned earlier, good optics being an investment.
I talked with a chap many years ago when I was buying some gear from him. The old boy told me when he popped off, due to her lack of knowledge, his wife would probably get a dealer in, and nowhere near the value of his expensive glass. I wonder how many members here have made suitable arrangements for their cherished, expensive kit? I know I haven't, and should do something about it now. Cheers.
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It will all be over by Christmas. |
#14
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All catered for in my will.
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#15
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Just noticed this old thread, forgive me adding a couple of extra points, might be of use to someone.
I have an El-Nikkor 105 N for 6x9 printing. I don't know if there was a change to the optical design, from the earlier lens, however the 'N' version almost certainly has better coatings. This will be most relevant for colour work though. Quote:
It is approx correct however for Plasmats and Double-Gauss lenses, and some simpler, symmetric lenses. This Nikkor lens ( like Symmars ) is a Plasmat. The fall-off rate is affected by the angle the off-axis principal rays come through the stop, and also the angle they ultimately make when they hit the image plane. These parameters are construction-dependent. With Super-Angulon types, and symmetric wides like the Leica M ones, you get about cos^3 (Ө) falloff . With inverse-telephoto wides for SLR's, it's as low as cos^2(Ө) . |
#16
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Advanced optics
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I am considering buying a very expensive lens for architectural photography - the 40mm Hasselblad Distagon. It is roughly the same price as a SWC with a 38mm Biogon. Reviews suggest that the Distagon suffers less vignetting compared with the much simpler Biogon. Can you explain this? Obviously the angle of rays subtended at the film surface is less extreme on the Distagon because the design must allow for mirror movement - the SWC has no mirror. But is that it? |
#17
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Where did you go to college ?
I did the Imperial 'Applied Optics' course. Good question. You can find all the data on the older lenses here : https://www.zeiss.co.uk/consumer-pro...otography.html From what I can see, the 40/4 is not fully free of mechanical vignetting at f/8, but it ought to be by f/11, then it will be better - as you say - vs. the Biogon. The distortion is quite low for a retrofocus wide - only max 1%. The 'T' field resolution at higher frequencies isn't great - as with a lot of 1970's/80's Zeiss designs. This is due to secondary lateral colour. If you can use the lens with a yellow or orange filter, the fine detail sharpness will improve quite a lot. Both lenses have a negative front group, which decreases the off-axis angles through the stop. However the Distagon has a positive (only) rear section, and a longer back focus, which keeps the principal ray angles lower at the film plane. In the Biogon, those angles increase again through the rear negative group, so the obliquity is greater for the off-axis fields. So, the answer to "is that it ?" is yes. That makes the difference of one Cos factor. Hope this makes some sense. |
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