Videotaping Observations

Brian Hunter (bkh@chem.QueensU.CA)
Fri, 2 Jul 1999 10:19:35 -0400

I have been experimenting with using a small television camera as a
supplement to visual satellite observing.  (Bart: How's that for a sneaky
way of staying on topic?)

As some of you know, my standard observing tool is an 80 mm. f/5 refractor
on a simple alt/az mount.  I purchased a ccd-based low light level
television camera and have it mounted on the end of the elevation axis
opposite the telescope.  It is mounted on a 135 mm focal length camera lens
( 48 mm aperature ) and connected to a VCR.  The two 'telecopes' are pointed
in the same direction so the VCR carries a complete record of what I am
looking at.  The camera has a built in microphone that picks up the clock
ticks generated by my computer and also any comments I make as I observe.  I
am sure that by now the neighbours have no doubts about my sanity.  Not only
do I have an observatory with a removable roof in my backyard, but I go out
there at night and talk to myself.

The camera is a P23C from Supercircuits Inc. in Leander Texas.
www.supercircuits.com ) It sells for US$80 plus shipping and handling
(about US$20 for me in Canada).  Mike McCants mentioned at Eurosom 3 that he
had purchased a camera fom them to try out.  ( Mike: Can you offer comments
on a different camera or is it the same one? )

The remarkable thing about this camera is that it is rated at 0.04 LUX
0.04 is not a typo! ).  This means that, with 48 mm aperture, I can see
stars down to 8th magnitude and satellites down to less than 7th magnitude
and occasionally fainter.  To put this in perspective, normal Iridium
satellites are easy to videotape and follow on the monitor and I have seen
fainter objects, such as Explorer 8, on favourable passes.  The downside is
that the ccd chip is only about 10 mm across the diagonal and the field of
view, even with the 135 mm focal length, is only about 3 degrees.  I am
playing with other optics to try to find a combination that gives me a
larger field of view and better sensitivity.  I have a well stocked junk
box.

There are a couple of other minor problems.  The resolution is not great.
Especially on bright objects, there appears to be blooming from pixel to
pixel and I don't ever get pinpoint ( i.e. single pixel ) images.  The chip
is not cooled and, at high gain, the random background noise is quite
obvious.

What are the benefits?  First, in a recent 90 minutes session, I observed 38
objects but when I reviewed the tape, I found five more.  Three were ones I
had missed because I was distracted and simply wasn't looking at the correct
moment.  Two others were unexpected because I had not picked them up in my
prediction file.  One of those, 84065C USA 3, is a faint flasher.  Second,
because I can replay the tape, I can check timing, position, and flash rate
after the fact. Even with a three degree field, I can track most objects
unless they pass close to the zenith where alt/az mounts are notoriously
difficult to steer.

Cheers,

Brian


Brian K. Hunter,                              Department of Chemistry
Professor                                        Queen's University
bkh@chem.queensu.ca                 Kingston, Ontario
(613)-533-2620                               Canada   K7L 3N6
44 14'  N         76 30' W