35mm adapters and DOF charts/tables

M

msolid

Active member
i have a question that i'm hoping someone can answer for me. i would've thought that it would've been asked before but when i did a search, i didn't see any answers. maybe it's a dumb question but i'm just a noob - so sue me.

when using a 35mm adapter, what DOF charts/tables (if any) can i use to figure out my DOF? i know that there are online DOF calculators out there, but i'm not sure what format i'm supposed to say that i'm using. i'd guess it would be 35mm still film since that's what lenses i'm using, but i'm not experienced enough to know for sure.

can anyone enlighten me on this? thanks.

oh, and not sure if this affects the answer at all, but the rigs that i'm using are a dvx or hvx with a sgpro rev 3 or brevis flip - nikon mounts.
 
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It's never so easy. It all depends on how far you zoom into the ground glass on these adapters. If you're using a dedicated relay lens adapter, like the mini35, you can just use the 35mm cine charts and be good to go. But with the adapters that mount to the front of the lens, where you can zoom in, you'd have to know what field of view you're getting before knowing what chart would be appropriate. Some, like the Brevis and Letus, allow you to see the full still frame; others might not. If you want to replicate the look of the movies, you'd normally want to zoom in to where you're getting a 22x17mm chunk of the ground glass as your full frame. If you do so, you'd then use the cine 35mm chart for DOF calculations.
 
Thanks for the informative answer Barry. I appreciate it very much. Now it's my turn to follow up with another noob question. What process would I follow to know whether or not I'm zoomed in properly to get a 22x17 mm chunk of the ground glass? I usually just zoom in far enough to where I can't see any edges on the adapter or any more vignetting and then adjust my focus to the GG grain.
 
I would have thought the measurements for depth of field would stay the same no matter what sensor size you use in the calculations. An F1.4 lens focused at 1m will have 1-1.05 meters depth of field no matter what the crop factor is from zooming?
 
DOF depends on circles of confusion - ie.e how much " out of focusness" is acceptable. If you zoom in on the image you are increasing the size of the circle of confusion so its somewhat akin to using a longer lens.
Likewise the DOF for a video screen would be different than for expected projection which is what most DOF tables are based on. So as Barry said its not so easy. You are probably in the ball park using a standard DOF 35mm table and then check a few lenses and draw your own conclusions as to whether they are accurate. No one here has ever studied the issues carefully and run tests that I know of.

Lenny Levy
 
thanks for contributing to this discussion. anyone have any suggestions on how i would carry out barry's suggestion to get a 22x17mm chunk of the ground glass as my full frame?
 
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