Question about shims and spacers

I have a lens I know is not in its original shutter. Photographic
results appear fine, but I'm curious how I could determine if this
lens should have any shims. Is there some relatively simple
test I can do on my own, like photographing the stock quotes
pages from the newspaper? Or would I do better to send it to
someone with optical skills for assessment? Any suggestions?

Thank you.

Steve

Stephan Goldstein wrote:

I have a lens I know is not in its original shutter. Photographic
results appear fine, but I'm curious how I could determine if this
lens should have any shims. Is there some relatively simple
test I can do on my own, like photographing the stock quotes
pages from the newspaper? Or would I do better to send it to
someone with optical skills for assessment? Any suggestions?

Which lens and shutter? Some designs such as a Dagor and some
symmetrical lenses are sensitive to spacing errors and may require
testing to minimize astigmatism across the useful field of the lens.

The easiest way is to set up a transilluminated USAF test target
about 30 feet from the camera. Substitute a sheet of plain glass for
the camera's GG, stop down to f/11 and look directly at the image
with a 10X-20X loupe. Adjust focus and determine the difference in
extension required for the sharpest radial and tangential images. (It
probably will be a fraction of a millimeter). Do that from the center
to the edge of the field. If the spacing is off, the distance between
the two focus points will increase markedly, usually at the edge of the
field. Turn the front or rear cell out a fraction of a turn, and test
again. If the deviation at the edge of the field decreases, repeat with
increased spacing. If not, you're done, unless you want to do some metal
work to test positions smaller than the shutter spacing.

Alternatively, you may see a small increment in one direction, no
difference part way out to the edge, and an opposite increment at the
edge. In that case, the anastigmatic focus points cross-over, and the
lens may be at its best compromise spacing.

In article y9Lpf.1600$Fo1.935@trndny07, Michael Gudzinowicz wrote:
Stephan Goldstein wrote:

I have a lens I know is not in its original shutter. Photographic
results appear fine, but I'm curious how I could determine if this
lens should have any shims. Is there some relatively simple
test I can do on my own, like photographing the stock quotes
pages from the newspaper? Or would I do better to send it to
someone with optical skills for assessment? Any suggestions?

Which lens and shutter? Some designs such as a Dagor and some
symmetrical lenses are sensitive to spacing errors and may require
testing to minimize astigmatism across the useful field of the lens.


It's an APO-Sironar W in Copal 3. It's one of the earlier ones, not
marked "W" and without the colored stripe, but in terms of size,
weight, filter size, etc. it's definitely a W.

The easiest way is to set up a transilluminated USAF test target
about 30 feet from the camera. Substitute a sheet of plain glass for
the camera's GG, stop down to f/11 and look directly at the image
with a 10X-20X loupe. Adjust focus and determine the difference in
extension required for the sharpest radial and tangential images. (It
probably will be a fraction of a millimeter). Do that from the center
to the edge of the field. If the spacing is off, the distance between
the two focus points will increase markedly, usually at the edge of the
field. Turn the front or rear cell out a fraction of a turn, and test
again. If the deviation at the edge of the field decreases, repeat with
increased spacing. If not, you're done, unless you want to do some metal
work to test positions smaller than the shutter spacing.

Alternatively, you may see a small increment in one direction, no
difference part way out to the edge, and an opposite increment at the
edge. In that case, the anastigmatic focus points cross-over, and the
lens may be at its best compromise spacing.


Thank you, that sounds like a relatively easy thing to do at home.

Steve

Stephan Goldstein wrote:

[edited]

It's an APO-Sironar W in Copal 3. It's one of the earlier ones, not
marked "W" and without the colored stripe, but in terms of size,
weight, filter size, etc. it's definitely a W.

I wouldn't bother. The lens was designed for that shutter, and the
variations between them are insignificant.

If you had an ancient glob of glass out of a lost barrel and wanted to
set it up for ULF, it might be worth the effort.

In article lVTpf.19727$AG1.10895@trndny04, Michael Gudzinowicz wrote:
Stephan Goldstein wrote:

[edited]

It's an APO-Sironar W in Copal 3. It's one of the earlier ones, not
marked "W" and without the colored stripe, but in terms of size,
weight, filter size, etc. it's definitely a W.

I wouldn't bother. The lens was designed for that shutter, and the
variations between them are insignificant.

If you had an ancient glob of glass out of a lost barrel and wanted to
set it up for ULF, it might be worth the effort.

That's what I thought, too, until I was in Hong Kong a few weeks ago
looking at a used 150mm APO-Sironar-W in a Compur 1 for US$600.
It had a very thin shim for the front cell, which is what prompted my
question. I ended up not buying the lens because it had some marks
dead-center on the rear element coating, even though they were willing
to lower the price.

BTW, this was at Tin Cheung, who have moved to a new location.
They're now at street level on Carnarvon Road. Used gear is on the
second floor. It's an altogether nicer space than the old spot in the
arcade.

They also had a 210 APO-W, asking HK$11000..

Steve