[pure-silver] Re: Rodenstock Depth of Foeld/Scheimpflug Calculator
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 6 Jun 2008 17:38:52 -0700
----- Original Message -----
From: "Jim Brick" <jim@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, June 05, 2008 6:52 PM
Subject: [pure-silver] Re: Rodenstock Depth of
Foeld/Scheimpflug Calculator
Not recommended. DOF cannot be done by the numbered angles
and/or DOF
charts. DOF is done by looking at the ground glass with a
loupe and
tilting/stopping down until what you want in focus, is in
focus. This
is based on exactly 49 years of doing this - I was taught
this at
Brooks Institute of Photography in 1959 and it has served me
really
well since then.
But if you want it as a gadget to occupy some unused space,
then I
guess it would be good.
:-)
Jim
The problem with DOF calculators or charts is that they
are based on certain assumptions about what the eye will
perceive as sharp. The assumptions are not always true.
DOF can be confusing because some calculations are
based on constant resolution and some on constant percentage
of focal length. The former can be useful where lenses of
different focal lengths are used on the same camera for
images of the same size, the latter when comparing depth of
field for lenses of constant angle of view, that is for
instance, the depth at a given f/stop for a 12" lens used on
a 4x5 camera and a 45mm lens for a double-frame 35mm camera.
So, when quoting some "rule of thumb" for DOF make sure
which system its for.
Also note the the "effective" DOF will depend on the
visual angle for the final image. That is, if an 8x10 print
is made from a 35mm negative and compared to an 8x10 contact
print from an 8x10 negative the required resolution of the
35mm negative must be multiplied by that required of the
print. Ultimately, this also depends on viewing distance,
i.e., the size of the image at the retina of the eye.
There _are_ some applications, such as aerial
photography, where actual minimum resolution is important.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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