Explore Scientific PMC-Eight Mount

I bought a new mount for astrophotography. Besides passively tracking to keep my camera steady it has “goto” capability for locating objects in the sky. It was definitely a big decision, even on sale at C$500.

I’ve had it out twice on our balcony overlooking the beach in a rented Florida condo. I have a good view to the east and north but limited to maybe 35 degrees altitude and no view to overhead or the west. It’s still pretty brilliant though to be outside at night without being cold or assaulted by neighbours’ yard lights.

Homemade alignment assist.

The first challenge is to align the mount with Polaris. The mount has a borehole in the Polar axis that you are supposed to sight through but the field of view is very small. I made a prealignment tool from a rolled up paper stick to the side of the mount that gives me a six degree view. With the North Star centered in that it’s much easier to nudge it into the borehole.

The paper tube and borehole got me roughly centered on Polaris and I went on to poke around the sky and take a few test pictures. At the end of the session I remembered reading about Photo Polar Alignment and I took two specific pictures of the Polaris area with the scope slewed 90 degrees between pictures. I used astrometry.net to solve the two images to see how I had done. The centers of the two images were about 1/2 degree apart which would probably be great for visual work but not great for astrophotography.

I downloaded a Python script called photopolaralign(PPA.PY) and ran it on my two images. This indicated that I needed to shift the mount 40′(arcminutes) – 2/3 degree laterally; and 18′ – 1/3 degree vertically. I’ll try it tonight in realtime – it’s supposed to be clear.

Photopolaralign: The X is where I am pointing, the green crosshair is where I should be.

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