I just set up my 8x10 and my 35mm side by side on the same subject. The 8x10 is wearing a 14 inch Heliar about (350mm), set at f/4/5.6 split (it's WFO), no movements. The 35 is equidistant and set to the same approximate FoV, happening in this case to be about 70mm on a 24-70, making the subject (a small doctor Dr. Suess christmas tree on my window sill) the same size relative to the vertical part of the aspect ratios (the Heliar could easily cover a longer ratio), at f4/5.6 split. Only front part of the tree is in focus on the 8x10. The window frame behind it is decidedly bokehed. Nothing outside the window is discernable at all. With the DoF preview pressed to set the 35mm aperture to 4/5.6, focused on the christmas tree, similar FoV, all of the tree and the window sill are sharp, and I can easily make out the house number on the house next door. The exposures would be exactly the same, the FoV's very similar, and that's what even is where the rubber meets the road outside of a calculator. Dropping the aperture on the 35mm to 2.8 (thats as fast as my 24- 70 is) doesn't buy much of anything at all. Another stop and a half still wouldn't get it even close, and indeed stopping the Heliar to f8 doesn't change much in relation to the deep DoF of the 35mm camera at 2.8, which is still has far greater apparent DoF, and that's three stops of difference.
Originally Posted by Rudeofus
In practical application both my experience as a multi-format shooter and this test indicate that no matter what you calculated, the reality doesn't fit your interpretation. At similar apertures and similar FoV's larger formats have far less apparent DoF. What I think is overlooked is that while DoF is a constant relationship to aperture and focal length, in application across formats, FoV for film size for a given focal length isn't, and so apparent DoF for the same FoV isn't either.
When I put up the Turner Reich Triple at 25 inches, at a portrait distance, I'm lucky to get more than an eye without stopping down.
Don't make me make these negatives.
Last edited by JBrunner; 01-23-2010 at 05:32 PM. Click to view previous post history.