Star Trailing.

[donboy]

Hi Robin,

The issue I'm having this past week is that one of my two scopes that are physically attached to each other has major star trailing.

I have a RASA 8" with a Uranus C Pro 585 that has major star trailing this week while live stacking and single long exposures. While my 51mm refractor has no star trailing with perfectly round stars.

I had this same setup running the previous week with version 4.1.11137 and this past week with 4.1.11239. Also switched over this week to SC Plate Solving.

Is it possible that the Player One camera could be shifting the image like dithering does? The RASA stacked images have a black border (like dithering) where the 51mm refractor has no border. I'm stumped for I can't find anything physically wrong with the RASA setup and the fact that it didn't show up until this week and the fact that the other attached scope show absolutely no signs of drifting or star trailing.



Don

[admin]

Hi Don,

I've never heard of an issue with a camera shifting the image like that, so I think it's unlikely.

My first 'check the plug' suggestion would be to make sure you are sill tracking at sidereal rate and haven't got lunar or solar rate selected, but if the second scope on the same mount shows good stars then that is unlikely. Next would be to check again the mounting of the RASA8 and the camera onto the RASA - any flex there could cause issues on the RASA but not for the other scope.

Are you capturing with both scopes at the same time and seeing trailing on one and not on the other?

cheers,

Robin

[donboy]

Hi Robin,

Yes I'm imaging with both scopes at the same time and there is trailing with the RASA and the Player One 585 and not with the 51mm with a ASI2600. With the 51mm setup I'm stacking using 5 min exposures and the RASA/Uranus Pro 585 I initial have to start out using shorter exposures of 90 sec and eventually increasing it to 4 min exposures. If I try to image initial with the RASA at anything over 120sec I get star trailing. The 51mm setup is attached to the RASA's top dovetail and never shows any signs of star trailing.

Last night I imaged using the method of progressively increasing the exposure time for the RASA setup and all went well, accept one time when I accidently set the exposure from 120 sec to 8 min and the image shifted quite a bit and the session was ruined with the image moving about 1/8 of a frame.

One livestack session I had last night I started out with 4min exposure with the RASA setup and it caused star trailing the was curved and very, very elongated curved trails.

Don

[admin]

Hi,

I'm guessing that the RASA/IMX585 will be about twice as sensitive (longer focal length ~400mm, smaller pixels 2.9micron) than the other scope (guessing ~250mm focal length, 3.75micron pixels), but it sounds like the difference is far more than that.

OK, so if the 51mm is piggy-backed then the tube of the RASA must be tracking correctly otherwise you would see trailing on both, so the likely candidates for movement come down to the camera (focuser/etc) on the RASA or something internal to the RASA (mirror shift like an SCT?). Could it be that the mirror inside the RASA is sensitive to moving the scope around, and when you move it to a new position, it sags a bit - that movement would slowly settle allowing you to get longer exposures as time passes.

cheers,

Robin

[donboy]

Hi Robin,

Settling of the mirror is something I’ve considered and hopefully will test it out tonight if skies cooperate.

Don