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View Full Version : f stop for max. sharpness on Xpan



Vincent Brady
09-27-2009, 03:17 PM
I came across a statement today saying the best f stop for max sharpness when using the XPAN was f8 and not f16 or f22. Can this be true or should I just test it out for myself.

Cheers
TEX

David A. Goldfarb
09-27-2009, 03:22 PM
It probably depends on the lens, but I suspect it would be around f:8-11 for that format. Stopping down further with the wider lenses should give more even illumination in the corners.

keithwms
09-27-2009, 03:24 PM
Yep, f/16 is going to be diffraction softened already. f/8 or f/11 sounds reasonable for a typical 35mm RF lens. But try it for yourself!

Lachlan 617
09-27-2009, 05:05 PM
As a (perhaps too) general rule, maximum sharpness for a lens is somewhere between 2 and 3 stops below wide open (thus, the f4 45mm Xpan will be at its sharpest around f8-f11).

As Keith has mentioned, diffraction will probably set in around f16. Mind you, it will be so insignificant at f16 and on such a small format to be almost undetectable at f16 and probably even at f22.

Also, the untrained eye will see a greater DOF as sharpness, so you should not fear shooting at f22. But, as Keith (again) mentioned, try it yourself. Use a 10x loupe to have a look at 2 scenes shot at different setting and see if you can tell the difference, and if you can, is this difference a show stopper?

Lachlan.

keithwms
09-28-2009, 07:33 AM
There is one article by Ken Rockwell, fortunately absent his usual nonsense, that explains all this quite well....

http://www.kenrockwell.com/tech/focus.htm

Now, I happen to think that judicious use of DOF is far more important than such effects, and my 'nonmathy' way to go about this, which has served me extremely well with the mamiya 6: simply scale focus and this will ensure that you stop down enough... but not too much. When in doubt, take two shots. When in serious doubt, take three shots. Eat, drink and be merry.

TheFlyingCamera
09-28-2009, 09:01 AM
Also, bear in mind that the lenses for the Xpan are not 35mm lenses, but rather medium format lenses. The Xpan just happens to use 35mm film, but the lenses have an image circle large enough to cover at least a 645 neg.