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| p.1 #18 · Aurora Northern Lights Shooting question |
David Baldwin wrote:
I suspect that older manual focus lenses which have a hard stop at infinity (for example the Nikkor AIS type lenses that I was using in the 1990s) are much better than modern AF lenses which are designed to focus beyond infinity, relying on electronic AF or more recently live view to get things sharp. But such old school lenses were designed on the whole for film, which is alot more forgiving of slight focus errors than digital.
I would treat any lens with great suspicion until its infinity focus has been verified by actual test shots on stars. As I say, I have never seen any AF lens by any manufacturer give perfect infinity focus on stars just by using the scale . I suspect this is a by product of the AF era, and is perhaps also an acknowledgement that some lens designs have focus which changes with the ambient temperature.
Only trust a lens' infinity position after actual stellar photography. I don't believe that perfect scale infinity focusing is of much interest to lens makers. Most photographers just don't need it, but any errors will be painfully apparent on stars and digital at f1.4/2.
As Ronnie Reagan once put it (I think) "Trust, but verify". Certainly personally I only abandoned film for my own night photography once live view came out. Before that focus at wide apertures on digital was a form of russian roulette, very hit and miss. Live view or stringent pre trip testing are the only ways to be sure.
David. The canon goes way beyond infinity at the end stop. It is also geared to be much more sensitive which makes it harder to focus manually. When you go to infinity stop on both my zeiss's it is as sharp as focussing manually. I move back a wee tiny bit on the 25. This is not possible by memory in the dark with the 24 because you have to move back a lot. The zeiss are calibrated for focus stop at infinity. But as you say, its best to test it in good light. But I still say the zeiss are way easier to use in the dark because the canon goes way way past infinity at the stop.