[pure-silver] Re: Is your camera really in focus ?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sat, 31 Mar 2012 10:16:49 -0700
----- Original Message -----
From: "Myron Gochnauer" <goch@xxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Saturday, March 31, 2012 6:06 AM
Subject: [pure-silver] Re: Is your camera really in focus ?
Tolerances are greater in large format, but more things seem
to go wonky.
Sheet film holders can be quite variable, with Graphmatic
6-sheet holders being so consistently different that I
wonder whether they were using a different standard.
The biggest problem I have had with 4x5's - - - especially
Cambo SC II - - - is lack of parallelism between front and
back standards. The Cambo designs for the 1970's have a
Y-shaped yoke to which the uprights attach. Since it is
pretty common to carry the Cambo upside down, and set it
down on the tops of the uprights, the yokes tend to get
twisted or bent
I have not checked a Grafmatic for a time but I think I
found mine to be pretty close. remember that the design of a
film holder is such that the film is _supposed_ to be pushed
back against the plenum by the edges. It doesn't always seem
to be. Of course, you must measure the depth from the
reference plane (the holder edges) with film in it. I've
found that sheet film holders are all over the place. The
best are the Riteway holders, which are usually close but
the older wooden holders must all be checked on both sides.
I also have a bunch of old plastic holders (name escapes me
at the moment), out of perhaps a dozen not on was correct.
I use a measuring jig made of fairly thick aluminum
sheet laid across the holder and a depth micrometer to
measure the distance from edge to film. The thickness of
the plate is then subtracted. I measure at corners and
center. I think a lot of old holders are just warped with
age.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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