AstroTrac, Take Two

Despite the full moon, I got out with my AstroTrac, modified Canon 350D and Borg 45ED. With the light-polluted skies of NYC, I put a Lumicon H-alpha filter on and shot as low as ISO 100 in order to test with 5-minute exposures. The conclusion? The AstroTrac is tracking just fine for 5-minute exposures. But my shots show bloated stars and some indication of what appears to be coma which is not centered on the sensor center. I had thought the bloating might be due to this camera having a clear filter. It was modified by Hap Griffith two years ago and I think I asked for a clear filter. However, I also have a Hutech "UIBAR-FF" in place which is supposed to provide both IR and UV cutoffs, so I really wasn’t expecting any bloating due to IR coming through.

I do have two remaining problems. First is that I have something on the filter/sensor/something that really calls for flat fielding. This was most noticeable in my images of M31, but shows up weakly even in star fields so long as the background is exposed enough to not be really black. Second, I really need dark frames, particularly at higher ISO speeds. The 5-minute exposure with in-camera noise-reduction turned on is significantly better looking than the one without. Ugh. I don’t like the idea of a 50% duty cycle for imaging. That starts to put me back at film-like times for imaging. Okay, not quite, but still. Around here, night-time temperatures are fairly stable so I could probably get away with taking a few dark frames and manually calibrating later. I’m not sure how well that will work when I’m in the boonies and the temperature is falling all night.

Oh, and I have to rearrange the wiring harness I so carefully put together last summer for CCD imaging tracking with the Losmandy GM8. I need things arranged a little differently for the AstroTrac.

Uhm, and I need to make some kind of stand-off to elevate the ball mount further off the AstroTrac. When looking near the zenith with the Borg 45ED, the camera hangs down low enough to bang into the AstroTrac. I’d also like to be able to mount two cameras instead of the current one, but that will take a little work in the garage I’m not sure I have time for before we leave.