RC issues

[Norwich_lad_chris]

Hi all,

 

I'm looking for some advice. I have a 10" Astrosib RC which iv had for about 2 years (its seen limited use) but is still giving me issues. 

As you can see in the image below I have really weird stars and I cant seem to fix them and was hoping someone on here has any ideas or suggestions. 

The whole setup is - Astrosib 10" RC, Astro-Physics AP-CCDT67 reducer, Astrodon Filters and Starlight Xpress SXVR H694. I use a Takahashi collimation scope and SGPpro to autofocus (Moonlite motorised focuser). 

 

any help or suggestions appreciated.

 

thanks

 

[vlaiv]

Hi, and welcome!

This is rather strange, never seen anything like that, so I have no clue what might be going on, but I do have suggestion to get you started in detective work:

Start by removing all items apart from scope itself, do image of bright star and look for the same pattern. If there is no such pattern, then move to steps below, if there is such pattern next thing I would do is try different camera (borrow of somebody or try DSLR if you can find one) - just to narrow things down - when using just scope and camera - it has to be one of them that's causing the problem.

Next thing to do is start adding one item at a time and see if you spot the pattern - first focal reducer, then filters. If you find what is causing this, try using just item that without other items to verify that it is that exact thing that is causing trouble because it might be combination of things - like using that particular filters with that particular focal reducer that is creating weird effect.

Hope this helps.

[ronin]

Somewhere I have seen that "pattern" and like an idiot I didn't bookmark it. If I recall right it was reported as a spacer, full circumference one, that was too small and intruded into the optical field. Replacing it with a fractionally larger diameter item cured it. Slight problem is I do not think the artical referred top an RC but a refractor.

The alternative is slight pinching, but that looks evenly spread.

Will say I have only ever read of problems with an RC for imaging, and I know of one that has taken about a year to get set up, and the person who has it also has access to an optical workshop to check things and set it all up. Equally the person wants perfection. It seems the results can be good but getting to good is a long, difficult path. They are 2 hyperbolic mirrors and set up is very delicate and fragile.

 

[r3i]

A few folks reported similar star shapes with the Mk1 WO Star 71 refractor.  In this case they were caused by fixings on the lens cell protruding into the field of view, so I'd suggested checking along the light path of your setup and see if you can anything sticking out.