[TASS] Coming Up for Air #3

[Tom Droege <droege@WWA.COM>]

Last night I got the first "almost" good data since 10 August.  The
"almost" is because the V shutter was sticking.  A little oil fixed it.
The shutter is self adjusting, and is supposed to reset it's position each
time it opens.  It was sticking enough that it did not quite close.  So the
frames have a bright line down their center.  Good enough to see that
everything else was working.

There are a few ice crystals here and there.

There are still a number of things to learn from experience.  Like what is
the best lubricant to use on the lead screw and the shutters.  I will
probably go to graphite lubricant (brass on brass) for the shutter and moly
grease for the lead screws.  (SS on teflon).   I have had good experience
with the moly in a previous life.

Today I will update boards and production test.  Until the "problem"
returns, I have a system that I like.

The "mystery" base line problem disappeared when I switched cameras.
Previously I had switched cameras with their filters.  This time I switched
camera filter comginations.  This is black magic.  I suspect the problem is
still to be found.  But I will charge ahead and wait for it to reappear.

I almost have the ice crystal problem solved.  I suspect it will be solved
after I operate warm for a day to give the desiccant a chance to absorb all
the water.  I have not gone more than a few hours without opening up a
camera.  It takes time for the desiccant to grab all the water molecules.
I am now operating the cameras under a partial vacuum.  About 28" Hg.  This
is what you can get with one of those little plastic hand pumps.  I figure
I will just attach one to each camera system.  That was the original plan
for the Mark IIIs.  This level of vacuum will also allow me to get a little
colder.  It seems to be just on the edge of where a vacuum helps.

The "O" ring seals just don't do the job.  They were designed to make the
cameras small and easy to work on.  It is not a recommended seal design.
So I solved the problem by just sealing up the camera with wax and a
soldering iron.  This makes a good seal, and is easy to break free if one
wants to open the camera up.

Tom Droege