Last night tracking with Mach2


Roland Christen
 

Hi Astronuts,

I was busy yesterday testing mount software in our AP observatory. After dusk I noticed the sky was very dark - very low humidity, and good seeing. So I captured a number of unguided images of the Ring Nebula just for fun. 160 EDF refractor on the Mach2. Below is what I consider a successful imaging session.

For those needing an explanation of the pix below, I modeled a path for the object by measuring the position of 4 stars along the path. Took about 1 - 2 minutes per star to center them and add it to the model in the CP controller. The image shows how the RA axis moved over a 1 hour time period, starting when the object was approximately 3 hours from the meridian. This motion of the RA axis is a very close match to how the object actually moved across the sky. The difference or error in that 1 hour exposure was approximately 2 pixels. I took a number of 600 second exposures during that time with results as you can see in the image below.

What would have been the difference between modeled tracking with the Mach2 versus guiding? The main difference is in the smoothness of the tracking. Guiding would almost always impart a back and forth sawtooth motion, which can be very small on a premium mount, but can be several arc sec P-P on a lesser one. With fast optics and modern astrocameras, it's getting so that 10 minute exposures are plenty for even the faintest stuff. And for that you can model with a minimum of points along the object path.

Rolando

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