When computing depth of field with various formats it's necessary to
recognize that larger formats require less magnification to produce a
given print size.
DOF is ultimately dependent on the resolution achieved on the film or
sensor in combination with the print magnfication. 30 lp/mm is enough
to make a sharp looking 8x10 print from a 35mm negative. For the same
final print resolution using the E-1, however, we need to capture 60
lp/mm but only 12 lp/mm for a 6x9 negative.
That said, the shorter focal length lenses on the smaller format cameras
still yield greater DOF in the final equivalent print. There is also a
significant difference in the hyperfocal distance.
Assuming an 8x10 print covering the same subject area and all lenses at
f/8 and focused at 5 feet the DOF (rounded to nearest 0.1 foot) is:
Lens/Format DOF @ 5 foot focus Hyperfocal distance
25 mm on E-1: 3.8 - 7.4 feet 15.5 feet
50 mm on 35mm: 4.3 - 5.9 feet 30.9 feet
125 mm on 6x9: 4.7 - 5.3 feet 77.3 feet
Chuck Norcutt
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