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Old September 16th 12, 06:39 PM posted to rec.photo.equipment.large-format
Richard Knoppow
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Posts: 751
Default Turner-Reich 6.8 Series II NO. 2 Missing Part


"BillyBobby" wrote in
message ...

I have a Grundlach-Manhattan Turner-Reich 6.8 Series II
NO. 2 mounted in
an Ilex shutter that I want to sell.

It is missing the f stop settings. Looking for a
replacement

6.8 – 32
12 - 45
14 - 64

Bill




--
BillyBobby


You may have to have a new plate made and engraved.
Its easy to calibrate the iris for the stop number. You can
assume the marked focal lengths are near enough although the
actual focal length of production lenses varies a bit from
the "nominal" length. When the single cells are used on the
back of the shutter or barrel the effective size of the
entrance pupil is the physical size of the iris. When the
lens is combined so that the iris is seen through the front
lens you must measure the size of the entrance pupil, which
is simply the image of the iris as seen through the lens.
The first step is to autocollimate the lens to find the
exact infinity focus. This is done easily by mounting the
lens on a view camera. You can get an accurate enough
measurement using the ground glass. Set a flat mirror
against the front of the lens. Use a penlight flashlight or
single LED against the ground glass, not quite at the
center. The mirror will reflect an image of the light back
to the ground glass. Focus it as sharply as possible. The
lens is now focused exactly at infinity. Now, using the same
small light against the ground glass place a translucent
screen over the front of the lens. A bit of ground glass is
ideal but paper works fine. You will now see a circle of
light projected through the lens. The diameter of this
circle is the diameter of the entrance pupil and the f/stop
is the focal length of the lens devided by the diameter of
this circle.
To make a stop plate mount a piece of thick paper or
card stock in place of the original plate. If you can mark
it with arcs matching the stop pointer. You can probably use
the stop pointer itself as a guide. Now, adjust the iris
for the f/stop numbers you want and mark them on the card.
Shops that do engraving can make a new stop plate based on
this card.


--
Richard Knoppow
Los Angeles
WB6KBL