On Sep 22, 2005, at 2:29 AM, Frantisek wrote:
JK> According to the lens barrel DOF markings, everything between 3
feet
JK> and infinity should be in focus at f5.6. The DOF at 15mm is
Don't count on DOF markings. They are useless because they are
computed for 3-4x linear enlargement _only_. Imagine how small a print
would that be from the APS sensor!
The reference magnification for most camera lenses' DoF markings is
from whatever format to an 8x10" print size, regardless of format.
The reason for this is that, in general, once a print is made larger
than 8x10 inches in size, one tend to view them from further distance
which means effective magnification levels out.
Of course the DoF markings on older Pentax lenses were calculated for
35mm format; for 16x24mm format you need to stop down one stop from
the markings to acquire the same DoF with a given focal length.
The only exception to this that I'm aware of is the Minox 8x11mm
subminiature cameras, where they chose to consider a typical 4x5"
print as the reference for DoF. That's about a 13x enlargement for
that tiny format, so that was considered the appropriate reference
standard.
Godfrey
