From: jack@rml.UUCP (jack hagerty)
Newsgroups: rec.models.rockets
Subject: Astrocam Breakthrough
Date: 15 Aug 92 06:42:39 GMT
Organization: Robotic Midwives, Ltd., Livermore, CA

Well, I *finally* got what I would consider a decent photo out of 
my Astrocam/Delta II (the box-stock combination).

Before leaving for NARAM, I made three flights (C6-7) from the
park about a block from my house. The first was severely light 
struck, but had a regognizable image of houses and cars. The 
last had the dreaded "black frame desease" (a completely saturated 
negative).  The middle one, however, Mama Mia! It was just about 
the sharpest, best exposed image the marginal optics in that 
camera can provide. It looked like it was shot on a tripod! The 
best part is that it was looking straight down onto a parking 
lot with perfect white stripes on black asphalt so I can get a 
ground measurement to determine altitude.

At NARAM, I flew it three more times (also with C6-7's). The
first flight acted more like a C6-7/2 since it seems like Estes
left out at least half of the delay charge, and I got <4 sec
before ejection. Got a nice, sharp shot of the underside of the 
cumulonimbus (cloud) moving in ahead of the rain squall (no 
smiley, it really is a great cloud shot). The second flight again 
had black frame desease. The final flight was part of a three 
Astrocam salvo that included Tom Beach's dual, rear looking hack 
and (I think) Mark Johnson's B6-4 powered low weight/low drag
version. My flight was textbook straight up and pitched over,
almost photographing its own smoke. The image was generally 
good, if a little off center and slightly blurred due to motion.
Still, you can pick out the people, cars, prep tents and even
the Tripoli launch pads (the white Mantis pads used for the 
model rockets just blend into the white lakebed).

After both of the launch sessions above, I think I've come up
with a theory on the black frames that seem to plague me
about one launch per session.

The fit of the camera in the Delta II body is not especially
tight. I assume this is so the shutter string releases quickly
on the first motion of the ejection charge. However, the camera
is quite heavy as a nose cone, and what problem pops up when
you have a heavy nose in a loose fitting body? Anyone been 
reading the FAQ? The Lovelace Effect!

I think that the tightness of the camera depends on the 
rotational orientation of the camera in the body (it's 
a little different each time I prep it). If it's at all
loose, at burnout the camera can ride forward in the body 
and allow the shutter string to creep forward. If it's 
enough to let the shutter hole anywere near the lens opening, 
you've got a completely saturated negative. 

This flash (ahem) of insight came after viewing the light
struck image mentioned above. At first I thought the camera 
had somehow caught the sun in the field of view, except that 
the camera was pointing almost exactly *away* from the sun at 
ejection. Also, the pattern of light damage was a circular 
reigion starting at the bottom of the frame and radiating up 
in a circular pattern.  I think the black frames occur when 
the shutter hole is allowed to actually breach the lens opening, 
whereas this frame had allowed only the barest crack of light 
in through the round shutter hole before the ejection charge 
released the string.

I've also come up with a way to beat the "flip the negative"
problem, but a lot of people don't read this far on long
posts :-) so I'll put it in the next one.

- Jack

=============================================================================
||Jack Hagerty, Robotic Midwives, Ltd.                 jack@rml.com        ||
||Livermore, CA		           NOTE! New, improved address! ^^^        ||
||(510) 455-1143	            (old ones will still work)             ||
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||               "Do or not do. There is no try." - Yoda                   ||
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