Filters - advice please.

[symmetal]

I don't think that Astronomy Tools calculator is any use for filter halos, only dust spots. With  my image I posted above with the OIII halos it says the problem distance is 1.56mm which is nonsense. To get a distance of around 12mm which is around the distance to the front protect glass the dust spot diameter needs to be about 500 pixels which is a more reasonable value, but still seems a bit large.

The filters are probably around 30mm away on the flt-98 and the calcuator says the dust circle would be 1300 pixels across which again seems larger than the typical filter dust spot diameter with this scope and camera.

The halos are possibly due to reflections between the two filter surfaces and the astronomy tools calculated distances seem to be more related to the filter thickness which maybe a clue. 🤔

Edited February 16 by symmetal

[Skipper Billy]

I have carefully inspected the entire optical train with a really bright torch looking for anything that is reflective.

The only thing I can see that is reflective are the screws that hold the camera together - see attached. (The inside of the scope is beautifully baffled and darker than a coal hole!)

Is it possible that light is passing through the filter hitting the screw heads and bouncing off the back of the filter into the camera causing the halos???

I am toying with the idea of making a mask to cover the screw heads from stiff black card and sandwiching it between the filter wheel and the camera.

 

Edited February 26 by Skipper Billy
Typo

[tooth_dr]

22 minutes ago, Skipper Billy said:

I have carefully inspected the entire optical train with a really bright torch looking for anything that is reflective.

The only thing I can see that is reflective are the screws that hold the camera together - see attached. (The inside of the scope is beautifully baffled and darker than a coal hole!)

Is it possible that light is passing through the filter hitting the screw heads and bouncing off the back of the filter into the camera causing the halos???

I am toying with the idea of making a mask to cover the screw heads from stiff black card and sandwiching it between the filter wheel and the camera.

 

Those are pretty shiny indeed!  Good idea to cover.  Wee black round stickers would be handy.

[Stuart1971]

1 hour ago, Skipper Billy said:

I have carefully inspected the entire optical train with a really bright torch looking for anything that is reflective.

The only thing I can see that is reflective are the screws that hold the camera together - see attached. (The inside of the scope is beautifully baffled and darker than a coal hole!)

Is it possible that light is passing through the filter hitting the screw heads and bouncing off the back of the filter into the camera causing the halos???

I am toying with the idea of making a mask to cover the screw heads from stiff black card and sandwiching it between the filter wheel and the camera.

 

If it was that, it would show on all filters and not just one of them…but still a good idea to cover, or swap them out one  at a time for Black headed ones..

[Skipper Billy]

4 minutes ago, Stuart1971 said:

If it was that, it would show on all filters and not just one of them…but still a good idea to cover, or swap them out one  at a time for Black headed ones..

True but I think i read somewhere (Vlaiv?) that Blue light and Oiii are more easily scattered than all the other wavelengths???

Cant do any harm so black insulation tape and sharp scissors required 🙂 

[Stuart1971]

5 minutes ago, Skipper Billy said:

True but I think i read somewhere (Vlaiv?) that Blue light and Oiii are more easily scattered than all the other wavelengths???

Cant do any harm so black insulation tape and sharp scissors required 🙂 

What do you get on images with no filter or just a plain glass filter ??

[Skipper Billy]

33 minutes ago, Stuart1971 said:

What do you get on images with no filter or just a plain glass filter ??

No problem with any other filters apart from Oiii and Blue - I am fairly convinced that the issue is with the filters and Baader are looking into it for me. Meantime I am just making sure that all other possibilities are explored whilst the rig is in bits and spread across the dining room table! 🙂 

[Skipper Billy]

Cant do any harm and may help a little??

 

[Stuart1971]

7 minutes ago, Skipper Billy said:

Cant do any harm and may help a little??

 

That looks superb…nicely done…👍🏻