A helpful note for any Alpa users working with HPF rings on the Rodenstock 40mm f/4 HR, the Schneider 60mm f/5.6 XL and/or the Schneider 90mm f/4.5 Apo-Digitar: I got curious about whether these lenses exhibit focus shift. The short answer is, 40mm and 60mm, yes; 90mm, no.
I shot some tests at a distance of roughly 1.8m to the LensAlign chart, in order to see small differences in focus placement. (The minute adjustments I suggest below would probably make very little difference when focusing at great distances.) Here's what I found and what I'm doing about it:
40mm:
Focus moves slightly farther away as you stop down from f/4 > f/5.6 > f/8. Since I figure I'm shooting at f/8 whenever possible with this lens, I adjusted my HPF so that focus is dead-on at that aperture (using a Leica Disto D5 for measuring distance to the LensAlign). Therefore at f/5.6 and f/4, I'll be slightly front-focused.
Compensation determined through brief trial and error:
To shoot at f/5.6, focus 1 degree farther on the HPF ring than your Disto reading. To shoot at f/4, focus 1.5 degrees farther than your Disto reading.
60mm:
Again, focus moves slightly farther away as you stop down from f/5.6 > f/8 > f/11. Since I figure I'm shooting at f/11 whenever possible with this lens, I adjusted my HPF so that focus is dead-on at that aperture (using a Leica Disto D5 for measuring distance to the LensAlign). Therefore at f/8 and f/5.6, I'll be slightly front-focused.
Compensation determined through brief trial and error:
To shoot at f/8, focus 0.5 degrees farther on the HPF ring than your Disto reading. To shoot at f/5.6, focus 1 degree farther than your Disto reading.
90mm:
No focus shift.
I shot some tests at a distance of roughly 1.8m to the LensAlign chart, in order to see small differences in focus placement. (The minute adjustments I suggest below would probably make very little difference when focusing at great distances.) Here's what I found and what I'm doing about it:
40mm:
Focus moves slightly farther away as you stop down from f/4 > f/5.6 > f/8. Since I figure I'm shooting at f/8 whenever possible with this lens, I adjusted my HPF so that focus is dead-on at that aperture (using a Leica Disto D5 for measuring distance to the LensAlign). Therefore at f/5.6 and f/4, I'll be slightly front-focused.
Compensation determined through brief trial and error:
To shoot at f/5.6, focus 1 degree farther on the HPF ring than your Disto reading. To shoot at f/4, focus 1.5 degrees farther than your Disto reading.
60mm:
Again, focus moves slightly farther away as you stop down from f/5.6 > f/8 > f/11. Since I figure I'm shooting at f/11 whenever possible with this lens, I adjusted my HPF so that focus is dead-on at that aperture (using a Leica Disto D5 for measuring distance to the LensAlign). Therefore at f/8 and f/5.6, I'll be slightly front-focused.
Compensation determined through brief trial and error:
To shoot at f/8, focus 0.5 degrees farther on the HPF ring than your Disto reading. To shoot at f/5.6, focus 1 degree farther than your Disto reading.
90mm:
No focus shift.
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