Bad Collimation

While imaging the last couple nights, I noticed that the images were a little wonky. Upon initial inspection, I suspected guiding just wasn’t being great, as the stars had that elongated shape to them as though the guiding was oscillating a few arcseconds. When I began to study the images more, I noticed that the star shapes were “rotating” around a central point that was between the center and the bottom left corner. In this small area, the star shapes were good.

I decided to recheck the collimation, and noted that it was off of the center of the laser collimator by a few millimeters. Where the laser fell was about the area of the chip that the stars were decent. So, I finally learned what bad collimation is. Have a look:

This is a full size frame that I color calibrated and stretched so that the stars are very visible. Note how they have this rotational trailing to them that seems to rotate about the yellow star near the bottom left corner. It’s especially noticeable in the diffraction spikes of the brightest stars. This shows how bad collimation that is off center of the coma corrector can really mess things up.