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Weihan
4-Oct-2014, 13:18
Does anyone know what the optimal f-stop is for this lens at infinity?

Oren Grad
4-Oct-2014, 16:16
Depends how large a field you want to cover with optimal quality, and what sort of tradeoff you're willing to make between center and periphery. As you stop down you'll lose in the center of the field from diffraction but, up to a point, you'll gain around the periphery from aberration control. So your answer might be different for, say, working with 4x5 vs working with 6x7 cm.

FWIW, Schneider's published MTF's for the 47 XL cover only f/5.6 and f/22. Given that, and the fact that center-vs-periphery tradeoffs will be a matter of personal preference, the usual advice applies: if you need to split hairs over this, you should run your own tests.

Nathan Potter
4-Oct-2014, 16:57
I use this lens a fair bit and agree with Oren. The optimal aperture really depends on the subject matter you wish to capture. And by optimal I suppose you mean resolution.

In use, I typically focus only at the center since it gets progressively difficult to see an image toward the edge of the frame (in fact impossible at the edge). Many people use this lens in a fixed focus arrangement in schemes that approach a pinhole setup.

I use a hyperfocal chart which tells me the distance to focus on for obtaining a DOF from near point to infinity. I see from my data sheets that I most frequently use f/22 where for a COC of 40 Ám (12.5 lp/mm) I get a DOF from 4 ft. to ∞. For that setting the hyperfocal distance is 8 ft. - which I simply estimate. Even at f/22 I don't think you'll see 12 lp/mm near the edge of the frame with 4X5 format owing to a high degree of elongation distortion mixed with other aberration distortions.

Nate Potter

Weihan
7-Oct-2014, 18:22
I use this lens a fair bit and agree with Oren. The optimal aperture really depends on the subject matter you wish to capture. And by optimal I suppose you mean resolution.

In use, I typically focus only at the center since it gets progressively difficult to see an image toward the edge of the frame (in fact impossible at the edge). Many people use this lens in a fixed focus arrangement in schemes that approach a pinhole setup.

I use a hyperfocal chart which tells me the distance to focus on for obtaining a DOF from near point to infinity. I see from my data sheets that I most frequently use f/22 where for a COC of 40 Ám (12.5 lp/mm) I get a DOF from 4 ft. to ∞. For that setting the hyperfocal distance is 8 ft. - which I simply estimate. Even at f/22 I don't think you'll see 12 lp/mm near the edge of the frame with 4X5 format owing to a high degree of elongation distortion mixed with other aberration distortions.

Nate Potter

Is that a record for low resolution scores? I had no idea the res was actually so low!

EdSawyer
8-Oct-2014, 10:03
Generally, f/16 is the best tradeoff for this lens. f/22 won't gain anything in the corners, F/11 may gain some in the center but falloff and coverage on the corners will suffer.

Weihan
8-Oct-2014, 14:58
Generally, f/16 is the best tradeoff for this lens. f/22 won't gain anything in the corners, F/11 may gain some in the center but falloff and coverage on the corners will suffer.

THANKS ! I'm going to try a series of Los Angeles city-scape WA shots.