Finally had some good, if cold, clear nights here to star-test my attempts at collimating my GSO RC8 CF using OCAL electronic collimator. I had noticed the manufacturer had published a YouTube video on RC collimation :
https://tinyurl.com/26uuqyej which has a pretty reasonable english sound track and the video procedure was also clear enough. Only negative was they did not include a tilt adjustment segment, as presumably they didn't have one fitted to their RC.
So before starting the OCAL procedure, I used a well-collimated laser to check and adjust the tilt corrector to get the laser dot returning back exactly onto the centre of the bullseye. A simple and easy way to do this is to attach your smartphone on to the front spider with zip ties, so that it can see the reflection of the secondary mirror donut. Between that and being able to see the laser bullseye as you adjust the tilt corrector, it was pretty easy to get a reliable and repeatable result. This was done with all spacer rings and focuser in place as used with my 2600mc. Just minimise adaptors and make sure the laser is firmly attached to the 2" focuser. Rotate it to ensure the laser dot stays put on the donut. Don't proceed until you've achieved this result.
After this, do the OCAL as per the video, then rinse and repeat the laser adjustment. Last night star test showed a nice off-focus star donut, close enough that I didn't bother trying to improve further by adjusting the secondary mirror screws, just went straight to trying some galaxy snaps. I was pleasantly surprised at the result. Hocus Focus aberration tester in NINA says I still have some minor residual tilt, but I finally have an RC8 that seems to work OK. Attached pics show a NINA shot, obviously unstacked, and a stacked version done in APP with minimal processing. please excuse the dust donuts hiding near the centre galaxy. Too impatient to bother with cleaning the 2600 sensor.
Wish I could say that I had similar success with the C8, but I don't blame OCAL, just the sloppy floppy mirror design of the C8 and lack of precision focus and adjustment for tilt, etc. Compared to the RC8, it's like comparing an original 1960's mini to a 2022 Corolla. I've decided to consign it to Hyperstar-only duties, where most of these inbuilt deficiencies disappear. Even then, the latest Sharpstar stuff looks like strong competition.
The 1600mm/f8 flatter-field performance of the RC8 is also in my view far superior to either the 2000mm/f10 or 1300mm/f6.3 configurations of the C8. it's been a good scope, but time for Hyperstar only.
