Peter,
If we compare two cameras with different sensor sizes, under the
following conditions:
- Same focus distance (distance to subject)
- Same circle of confusion criterion (relative to image size)
- Same field of view (35 mm equivalent of focal length)
then the same depth of field performance will be achieved on the
two cameras with apertures whose f-numbers are proportional to
sensor/film frame size.
So, for example, on the 300D, with sensor size 0.63 of the size of
the film frame on a 35 mm camera, the depth of field performance
achieved on the 35 mm camera with an aperture of f/5.6 would be
achieved on the 300D with an aperture of f/3.5.
Looking at it another way (again under the conditions noted above),
if we look at hyperfocal distance as one indicator of depth of
field performance, then for the same aperture, the hyperfocal
distance on the 300D would be 0.63 times the hyperfocal distance on
the 35 mm camera. (Hyperfocal distance is that distance such that,
with the camera focused at that distance, all objects from half
that distance to infinity will be in focus within our circle of
confusion criterion.)
Thus, in summary, compared to a 35 mm camera (again under the
conditions noted above), the 300D:
- WIll give the same DOF performance with a larger aperture
- WIll give greater DOF for a given aperture.
Sorry to state all this in such an elaborate way, but simpler
statements comparing depth of field performance don't really work.
I hestitate to use the term "better DOF performance" since there
are some workers whose outlook is that smaller DOF is "better"!
Best regards,
Doug
