2004.12.09
With just one night to go before the Star Party on Friday, Bob and I got together again to make sure we could get his STV autoguider working. Setup for the evening was very quick because we had left the scope out from last night, so it was already polar aligned.
We put the eFinder tube and focal reducer onto the STV camera head which makes it a standalone 100mm f/4 CCD finder scope. This was attached to the piggyback camera mount and hand-tightened. Bob had played around with the STV hardware some but had never used it to guide the telescope, so that was our first task. After plugging in the 6-wire connector between the LX200GPS and the STV, we hit the auto-calibrate button and it started doing its thing but it was complaining about not being able to cause movement in the DEC axis (relays 3 and 4).
Turns out the time constant was set too short and the focal length and ratio was set for viewing through the LX200 rather than the eFinder. Once we fixed these issues the STV worked like a charm. We left the aggressiveness at 1.0 for both axes, but with the terrible seeing I suspect we should have dropped it down to 0.5 or so to prevent oscillation.
As soon as everything was working, we set about to recreate one of the M42 pictures from yesterday. Unfortunately, the STI Stiletto was still not doing anything for us. We both futzed with it but in the end, whenever we thought we had the best focus we could do with the STI (which was a huge grey area due to the dancing interference noise), I'd switch over to the camera and see the star as a big donut. I ended up just focusing through the viewfinder and the image suffered as a result:
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The Great Orion Nebula, M42, exposed for 20 minutes, ISO 100, ~3550mm EFL, f/10.
STV autoguider piggyback on OTA w/ eFinder (100mm, f/4). You can also make out
M43 to the upper left.
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The stars are big puffballs probably due primarily to the focus. I think the STV took care of significant vibration and imbalance problems for us. Notice that this is a 20 minute exposure as compared to the 30 second and 2 minute exposures yesterday. Guiding was more or less perfect. The average guide error given by the STV was about 1.2 arcseconds, though I didn't save an error histogram for this shot. We have got to do something about the focus!!