cshimokita[Photo Forum Moderator]
10714
Jad... I don't claim to be a technical person ; )
Aug 13, 2019,08:43 AM
The depth of field can be determined by focal length, distance to subject, the acceptable circle of confusion size, and aperture. The approximate depth of field can be given by the following formula:
DOF ≈ 2u2NC / f2
for a given circle of confusion (C), focal length (f), F-number (N) and distance to subject (u).
The point of the test shots was that even though the FOV between the two systems is considered to be "equivalent", the results are not the same... that while it's convenient to think of a 23mm lens and APS-C sensor and a 35mm lens and FF sensor as "equal", they aren't.
The DOF is calculated base on the lens focal length not the FF equivalent focal length... a 23mm lens renders as a 23mm lens regardless of the sensor size...
If I wanted similar DOF results I could calculate the f-stop for the Canon as follows (leaving the Fuji at f/2.8):
_____________________________________
DOF Fuji vs. DOF Canon
2u2(2.8)C / 232 ≈ 2u2(f-stop_Canon)C / 352
2.8/529 ≈ f-stop_Canon/1225
f-stop_Canon ≈ f/6.48 _____________________________________
IF my math is correct, and I would want to test that "theory" in the real world ; )
Casey
EDIT: the above is a simplified calculation that assumes a constant CoC for both cameras. This is of course not correct as the image from the APS-C would require more enlargement than the FF image if both are printed to the same size. The "standard" CoC for FF is 0.03 and for an APS-C sensor it's 0.019. If you factor that into the calculation the f-stop_Canon ≈ f/4.1. How about that ; )
_____________________________________
DOF Fuji vs. DOF Canon
2u2(2.8)CAPS-C / 232 ≈ 2u2(f-stop_Canon)CFF / 352
(2.8 * 0.019) / 529 ≈ (f-stop_Canon * 0.03) / 1225
f-stop_Canon ≈ f/4.1 _____________________________________
DOF calculations are a fun exercise, the proof is in the print... and here the consensus seems to be that a current day APS-C sensor can produce excellent prints to a reasonable size ; )