shims for apo-germinar?

[Craig Wactor]

I have been reading up on my recently received 600mm and 750mm apo-germinars (carl zeiss jena model). I believe they are missing the brass shims, the "trimmring" spacers that Arne Croell wrote about. There is a slot in the middle of these barrel lenses that you can open by twisting the lens. I am guessing this is where the shim should go. Is anyone aware of where these things could be bought? I am under the impression that they improve focus at infinity.

[Dan Fromm]

No idea about where to get shims, but the slot you mentioned is most likely for Waterhouse stops.

[John Berry ( Roadkill )]

The slot can also be used for filters.

[Craig Wactor]

Hmm... The lenses have an internal iris, f/9-f/128. Wouldn't waterhouse stops be redundant? I could see the filters though...

[Arne Croell]

The barrel versions were not made to use shims, only the shuttered versions. The slot is for waterhouse stops and filters, as mentioned above.

[Mike Gudzinowicz]

Craig,

It's unlikely that the spacer which is placed between the front cell and the shutter
is available. You can test your lenses by replacing the camera's ground glass with
window glass to faciltate focusing on the aerial image with a low power microscope.
Focus on a distant (5 M+) backlit target on axis, stop down to f/22 and check the
corner image. Unscrew the lens a fraction of a turn, refocus on axis, and compare
the corner images. If you determine the shutter thread pitch, you'll know the spacer
thickness to use from the number of revolutions. For ULF the correction may not
be noticed since the prints aren't enlarged very much if at all.

[Craig Wactor]

Thanks for the help, everyone!

[Merg Ross]

Re the Waterhouse stops, for photo-engraving they can be punched square and rotated to bring the square in different relative positions to the screen lines. No one asked, but having been a process cameraman years ago I couldn't resist the comment.