Changing Optics and Tuning Alignment

I’ve found the Celestron C9.25 very challenging to set up for imaging – the very long focal length was a challenge for the mount, and the relatively short back-focus distance was a challenge for guiding. I know it can be done, but I didn’t feel up to the challenge yet, so I have backed off.

Astrophoto-Autoguiding-Stack-IMG_0622So, I have installed this set-up instead: An AT8RC 200mm imaging scope, 1600mm focal length f/8, with a piggybacked guide scope. This scope is half the weight of the 9.25, so should be stable on the mount. It has a fixed main mirror, focusing only by the Crayford, and it has a long back-focus distance that accommodates my focuser and filter wheel easily. I am staying with the piggybacked guide scope for a while before tackling the additional challenge of fitting an OAG in place – we’ll see how well the guide scope performs. The whole setup is very rigid so I’m expecting good results.

Last night I started tuning this setup. To start, I re-did polar drift alignment – I had noticed, in recent sessions, a lot of Declination correction by the autoguiding routine and realized that with good polar alignment and a solid mount there should be almost no Dec drift. So, I checked the alignment last night. Azimuth was pretty good, although I did a minor adjustment, but Altitude was off by several arc minutes. So, I tuned both with several iterations of the PEMPRO polar alignment routine, and have both axes correct to less than an arc minute.

I also discovered that I need to mount my counterweights in the other order, because I don’t have enough fine control of the weight for off-balancing the RA axis to the East using this setup. Next free night I’ll mount the weights in the other order and rebalance. (I like to arrange that one weight stays fixed in position, and the other creates a small imbalance to one side or the other by moving through a small range of possible positions.)

More status reports to follow as setup progress.

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