On Nov 13, 2008, at 12:31 PM, John Celio wrote:
http://www.dpreview.com/lensreviews/pentax_50_1p4_p15/
One thing that confuses me was this text about the distance scale:
"A distance scale is provided with ... a depth of field scale marked
for
F11, F16 and F22. As a legacy film lens, this is calibrated for the
35mm
full-frame format, and will therefore be somewhat over-optimistic on
APS-C DSLRs."
How can DOF be affected by a cropped sensor? The lens itself hasn't
changed at all, just the image-recording surface area.
The recording format affects the magnification and field of view. DoF
is calculated based on those two elements, in part. EG, using
DoFMaster, comparing 50mm on film SLR @ 10', f/5.6 with 50mm on DSLR,
f/5.6 @ 10':
film DSLR
near limit 8.31 8.81 ft
far limit 12.6 11.6 ft
total 4.25 2.76 ft
hyperfocal 48.5 72.7 ft
CoC 0.03 0.02 mm
FoV using Rui Salgueiro's field-of-view calculator:
H V D
film 39.56 27.0 46.8 degrees
DSLR 27.0 18.2 32.2 degrees
So you can see they're close, but a little optimistic for the DSLRs
due to the smaller format and tighter FoV.
The distance scale and DoF markings on the 50/1.4 are too crude to be
of much useful value anyway, imo, regardless whether you're using a
DSLR or a 35mm film camera. Most DoF markings are too optimistic.
Godfrey
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