Halos around Stars

[wsteel33]

Hi Guys

I have just added the Orion 0.8 reducer/flattener to my image train. Don't know why I waited so long the extra speed of data collection alone (turning my f/7.5 Orion 80ED into a f/6) was well worth it.

However, I have found I get a halo around bright stars.

Anyone got any advice of how I can deal with this.

I have only managed one significant session with this new set-up (bloody British weather!!) so it may just be this  image but I never had this issue before I added the reducer/flattener. I notice a the halo is red too around what should be a bright blue star. I like my star colours to come out as natural as possible (don't we all?)

Any advice would be gratefully received.

FYI the set up is an Orion 80ED, Orion x0.8 reducer/flattener, modded Canon 600D with SkyTech CLS-CCD clip in filter for EOS (all on an ES EXOS2 mount). 

I have attached the photo for reference. The star is Xi Persei in the bottom right of this California nebula image.

 

Cheers

Wayne

Edited December 9, 2020 by wsteel33

[Whirlwind]

Halo's are a result of reflection within your imaging train. 

It is likely that the filter is reflecting some light back up the imaging train and which is then reflecting off the reducer back towards the camera.  

You won't have seen this before because if any reflection did occur it would be from the main telescope lens which would have by that point been so out of focus you would never notice it.

Some filters/reducers don't have great anti reflection coating (especially at the Near infra-red and given that you are getting red halos I would guess it is around this wavelength that the light is being reflected.

Sometimes flipping the filter the other way round can help (some have a 'shiny side'.

Otherwise it may just be finding a better filter.

 

Edited December 10, 2020 by Whirlwind

[wsteel33]

1 hour ago, Whirlwind said:

Halo's are a result on reflection within your imaging train. 

It is likely that the filter is reflecting some light back up the imaging train and which is then reflecting off the reducer back towards the camera.  

You won't have seen this before because if any reflection did occur it would be from the main telescope lens which would have by that point been so out of focus you would never notice it.

Some filters/reducers don't have great anti reflection coating (especially at the Near infra-red and given that you are getting red halos I would guess it is around this wavelength that the light is being reflected.

Sometimes flipping the filter the other way round can help (some have a 'shiny side'.

Otherwise it may just be finding a better filter.

 

Thanks Whirlwind.

The filter is a pretty good one and well reviewed, it is a clip-in one which I believe is supposed to go in one way around. I checked anyway after your comment and it looks to have the same coatings on both sides anyway.

Its the only clip in filter I plan to buy and I am going for 2'' mounted ones going forward that will screw into the front of the reducer/flattener and may replace this one eventually (budget wont stretch to that just yet).

Guess I live with the halo's for now in the sessions when I am using this particular filter and reducer combination.

Thanks anyway.

Clear skies (hopefully sometime soon) 🪐💫

[Chefgage]

I have the same issue. It became more apparent after modifying my DSLR. I then got a better lens (Samyang) rather than using the cheaper lens I had. This improved matters but it's still there. After a bit of reading it appears that the cls clip in filter could be the culprit. Depending on the setup this can cause the red halos (I notice it when focusing using live view). 

I have not tried imaging without the cls in RGB. I do a lot of just Ha so do not see the red halos because of the Ha filter. So this leads me to think yes it could be the cls. My next session is going to see if this is the case

 

Edited March 10, 2021 by Chefgage