Originally posted by zx-m Thanks, Dave...you are right: this is rather complicated, much more than I had imagined. I suppose this is why I have ignored digital for so long.
I thought the "full frame" (3:2 or 2:3) designation of cameras such as the K-7 and D300 would make for easy, accurate printing. I suppose I have a rough understanding of what you are trying to explain, but I do not fully understand the concept. I am trying to determine if a 2:3 print (say a 4"x6") will offer the same DOF as it would with an SLR. It seems to me that if things work in the manner in which I understand them (which could be incorrect), then I would be getting something like a 50% increase in depth-of-field in using a manual focus lens on a DSLR--that is, the DOF of a 50mm focal length would be more like that of a 35mm focal length.
I'm sorry, by "3:2" I meant it is necessary to enlarge the APS-C print by a ratio of 3/2= 1.5X to match the print size from a full-frame camera.
Stated another way, when focused on a particular subject at a particular distance the same lens throws the same image on the sensor plane for both cameras, so at that level the DOF is the same.
However the smaller APS-C sensor only captures a central portion of what the full frame's sensor captures.
To make the same sized print from both cameras you've got two choices:
(1) set the enlarger so the size of the subject (eg. a face) on the easel is the same. In this case the print from the full frame camera will be larger, it so must be trimmed with scissors to make the two prints the same size. The two resulting prints will be identical with identical DOFs.
(2) grab a piece of 8x10" paper (for example) and enlarge what was captured by the sensors just enough to fill the paper. In this case the APS-C sensor's image will have to be enlarged 1.5x that of the full frame sensor's image (the face on the ASP-C print will be 1.5 times bigger.) This has the effect of altering the effective DOF.
I hope this helps clarify what's going on rather than adding to the confusion.
The rules given most places about DOF, sensor size, etc, assume you'll follow the second of the above alternatives with the result being DOF is increased by the crop factor (1.5X in this case).
Dave in Iowa