OK, here is the cinerio. Your shooting a head & shoulders portrait on 8x10. You first use a 300mm lens at f16. Then you switch to a 450mm lens. Move the camera back a bit and compose so the head is the EXACT same size on the ground glass as with the 300mm. Stop down to f16,is the depth of field the same with the two different focal lengths? My gut tells me yes....but?
Rich
Yes
No.
Well, that's settled.
Jim, how can you say that? DoF is controlled by magnification and aperture. See any good book on closeup work, e.g., Lester Lefkowitz' The Manual of Closeup Photography.
See!?? This is why I don't gamble. You have a fifty fifty chance, and blooooey.
Correct. Aperture and magnification. One type of magnification is the format size. If you take a 50mm lens and use it on an FX DSLR, it will have one less stop of DoF than it would on a DX lens. DoF is affected by format size.Originally Posted by Dan Fromm
300mm, f/16, 10ft, DOF = 1.97ft
450mm, f/16, 15ft, DOF = 1.96ft
It's not just "a little ways back," it's a good five feet. But yes, the DOF will remain the same.
For a 5ft distance, you'd need to move back to 8ft. So +50% focal length, +50% distance to move back to maintain DOF.
"It's the way to educate your eyes. Stare. Pry, listen, eavesdrop. Die knowing something. You are not here long." - Walker Evans
No. Fudge factors are affected by format size.
The DoF as calculated by various algorithms includes a fudge factor based on the supposed magnification
from the film to the final print. That fudge factor may or may not be valid for any particular image.
The depth of focus in the film emulsion is completely unrelated to the size of the film.
- Leigh
If you believe you can, or you believe you can't... you're right.
Depth of field is precisely the same, but magnification of the background is greater with the larger lens which will make it appear softer.
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