Quote:
Originally Posted by Startrek
How’s your collimation ? Maybe re collimate the OTA as best you can get
Secondly did you check or Re balance the mount / scope first to ensure you are properly balanced in Ra and Dec ( and slightly east heavy in Ra )
Are you balancing Dec correctly with the mounts Ra axis horizontally level and locked so the Ra axis and OTA form a T shape, then rotating Dec 180 degrees both ways to find good balance.
Then you need to check the mounts tracking and polar alignment first , guiding can come later ( as per my previous recommendation )
When you say “PA seems good” did you perform progressive unguided subs on a test Star ( say mag 1.5 to 2.0 ) in the east ?
Starting with 30 sec , then 45 sec , then 60 sec , then 80 sec and review all for signs of poor PA ( Star shape )
Don’t just rely on your guiding software to tell you “PA seems good”
I always run an unguided sub of up to 60 sec or longer to check PA even though my PA says under an arc min
Then proceed on to other checks like tilt and guiding .....
I’d still try and get that guide scope out of that damn offset shoe bracket and bolt it solidly onto a Losmandy bar attached to the tube rings so it’s centrally mounted along the centre axis of that big OTA. A solid mounting and tightened guide scope and camera will minimise flexure !!! The bigger bar and bolts the better !!! Those shoe brackets are prone to micron movement as it’s just relying on the thin metal wall of the OTA with this 0.5 to 0.75 kg guide scope and camera and cable hanging out at 90 degrees up to 200mm with various torque applied when the OTA slews to different angles
That’s enough for now .........
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Martin, some great comments. Thank you for taking the time to write that all up. Collimation is good, I’ve tried collimating using different techniques. All work fine, but don’t fix the elongation, so I don’t think collimation is the issue. Next you mentioned something that interests me that I’ve heard before but never applied: RA slightly East heavy. How much is slightly East heavy? Half a counterweight away from perfect balance? I do the T shape when balancing Dec, but must admit I don’t lock RA. I might try that too.
I tried your previous experiment up to 60 seconds. The star looked good. But I will try 80 seconds next time too.
I will purchase a Losmandy bar. Everyone seems to recommend this. I’m just not that good with all the DIY. I’ll give it my best shot. I’m convinced it will help.
Thanks so much, Martin. I have some more experiments to do. Please let me know how East heavy I need to go.
Regards,
Stéphane