Originally posted by Lowell Goudge if you take the same field of view with an ASP-C sensor camera and a FF camera, the DOF in the two images is different (assuming again the same aperture)
This is a true statement if aperture denotes an f-stop number, and a false statement if aperture denotes a diameter.
Not being precise here is the root of many rants
Note that aperture w/o qualification normally means the latter to opticiens and the former to photographers
Originally posted by octavmandru If I remember right the Zeiss formula was developed for engineers to know how good the lenses should be.
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That's why the medium format lenses are not necessarily better than the FF lenses, when used on FF, or 35 mm.
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Take K20 & 5D. Canon has a bigger CoC, but a smaller PDoF, since it has a lower pixel density, right? If you take the same picture with both cameras, and print both images on max. resolution (equal printed pixel size), the reasonable clear depth on Pentax is narrower than Canon's?
The Zeiss formula was reverse-engineered by early web sites from the DoF scale on Zeiss lenses. Obviously, Zeiss uses a tighter CoC when what is commonly used by DoF calculators (which is 1/1500).
The resolution of lenses is determined by ambition.
- Zeiss 35mm rangefinder: 400 lp/mm
- Zeiss 35mm SLR: 300 lp/mm
- Zeiss for Hasselblad: 280 lp/mm (Superachromat 5,6/250)
- Zeiss Large Frame: 160 lp/mm (Biogon 4,5/75)
So, at least for Zeiss, the resolution of larger frame lenses decreases more slowly than their image circle increases:
The latter (8x10") renders 5300 million pixels (1 shot Gigapixel
) where 35mm SLR is limited to 300 million pixels (divide all numbers by 5 or so for comparison at higher contrast).
Your question about K20D vs. 5D is ill posed. You must clearly state what parameters you keep constant. Canon has a bigger CoC (1.5x)
and bigger pixel size (1.3x). One really should only compare PDoF for some given
constant number of pixels (same goes for noise and dynamic range btw).