[pure-silver] Re: spoiled by my new lens
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 7 May 2007 23:09:13 -0700
----- Original Message -----
From: "Shannon Stoney" <sstoney@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, May 07, 2007 7:39 PM
Subject: [pure-silver] Re: spoiled by my new lens
>I think you must be sure your camera movements are zeroed
>out..... This is pretty easy to do.....
But in my opinion, Peter has hit on the most likely
problem.... your GG is in the wrong place relative to the
film plane.
I am not sure how to fix this.... any suggestions out
there if the GG is out of calibration? How can you tell
the right location?
Then, after you are sure the GG is in the right location,
you can test your film holders for correct location....
but test the GG
first.....
There is a piece of glass or plastic with a grid on it,
and then under that is a thicker piece of glass.
But, if this were the problem, then both lenses would be
affected, would they not?
--shannon
That is correct, if the GG is out of place it will
affect short focal length lenses even more than longer ones.
Check the quality of the image on the GG. See if you can
detect the same softness there. This will tell you if the
problem is the lens or something else. Ken Hough rebuilds
Deardorf cameras and knows his stuff. He's sent a good
checklist worth following up, but check the GG image first
to make sure.
If the lens _is_ soft it can be from a couple of things,
all unlikely but possible. One is an element out of place
because its fastenings are loose. Check the lens to see if
it rattles when shaken, it shouldn't. Also, Get the best
focus you can on the GG and examine a corner or edge of the
image while rotating the lens slowly in its mount. You
should see no difference in the image. If it does change its
an indication of a tilted element. Its also possible that
the lens had an optimizing shim on one of the cells. Cell
spacing can be checked by focusing on a very distant small
object (a star image is best) and adjusting the cell spacing
by turning the front element around a couple of turns. If
the star becomes sharper as you turn its an indication that
a spacer is missing. This can happen if the cells are
removed to clean them but, again, is unlikely.
If the GG image _is_ sharp but the negatives are not
then suspect the GG position or holder accuracy but, since
your other lens performs well these are probably OK.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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