Originally posted by snostorm Consider that with film, the only focus aids were split image and microprisms in the center of the screen, and lenses were no less sharp nor did they have shallower DOF. . .
Just for clarification -
for the
same angle view
the smaller format APS-C will have a greater DoF than the larger full frame 35mm format.
For the same lens - as you say will have the same DoF -
eg: a 50mm lens at the same aperture will have the same DoF -
However in practice, that lens gives an angle of view on the 35mm film camera of 50mm a "normal lens".
BUT on an APS-C this is the equivalent of 75mm (adjusting for the crop factor) and is really a short telephoto.
To get the same angle of view the APS-C would have to use a 33.3mm lens - and that will have a greater DoF at the same aperture.
Please see:
DoF at Wikipedia
"
When the “same picture” is taken in two different format sizes from the same distance at the same f-number with lenses that give the same angle of view, and the final images (e.g., in prints, or on a projection screen or electronic display) are the same size, the smaller format has greater DOF. "
BUT it's unfortunately slight more complex than that:
"
Many small-format digital SLR camera systems allow using many of the same lenses on both full-frame and “cropped format” cameras. If the subject distance is adjusted to provide the same field of view at the subject, at the same f-number and final-image size, the smaller format has greater DOF, as with the “same picture” comparison above. If pictures are taken from the same distance using the same f-number, and the final images are the same size, the smaller format has less DOF. If pictures taken from the same subject distance are given the same enlargement, both final images will have the same DOF. The final images will, of course, have different sizes. "