Stereo 225/Diacord update

[erker@xxxxxxxxxxxxxx (Greg Erker)]

  Dawn went out with the kids for an hour or
so last evening. So after I finished the dishes
I did some playing.

---
Test slide with glass spacers:

  I discovered that I need a thicker spacer
to have the projected slide in focus at
a reasonable distance (and size) with the
camera focused at infinity.

  I ended up stacking my 6mm and 5mm pieces
for a total of 11 mm spacer. Best focus was
at approximately 40" from the test slide to
the wall. I measure 20mm worth of projected
grid and got 22cm. So the magnification is
11.

  If you place your corner dots in a bit so
that they are 40mm apart. They will be 440mm
on the wall. The diagonal will be 622mm on
the wall. If you can measure to 1mm then
you could detect differences of less than 1/4%.

  One minor problem is that the point of best
focus isn't really obvious, at least with my
semi-wide grid lines and text. I would say I
was within +/- 1/4" of best focus. Which is
+/- 0.6% error in the measurement. With a better
focusing aid on the test slide (resolution bars?)
you may be able to cut that in half.

  So I think it may be best to find the best
focus for the first camera tested, then
place all following tested cameras at the same
distance from the wall. They won't be at their
best focus but you should still be able to
mark the center of a slightly fuzzy corner dot
accurately.  I think this will contribute less
overall error since the test cameras can be
placed at the same distance from the wall with
great accuracy: say 1/16" in 40" which is 0.16%.

  I'll try this out with my 225 and Diacord L
and maybe my two Ricohflex's to see how well
it works. I know from test rolls how much my
225 differs from my Super Ricohflex so maybe
I can re-prove it.

---
225 intermittent problem:

  It came back :(   And I had the front
panels off so I could see that the cocking
linkage was not the problem this time. So
it must have had two intermittent problems.

  This is quite bad news since 225's and
their shutters are quite rare*. My only hope
is that Sam can see some problem with it
when he opens it up to check for linking
ability.  Or it is possible my ebay 225
with the broken shutter has cocking problems
and the shutter module itself is okay.

  Needless to say I'm quite disappointed.

---
My insomnia is gone so I'm back to working
on this project in 15 minute chunks :)

Regards - Greg

* anyone know of a late 50's TLR with
Seikosha-SLV shutter? Cheap preferably.