Focal Reducer + asi533 = messed up image How do I fix?

[Quetzalcoatl72]

This is clearly a terrible image. Mainly because of the bad seeing being middle of june and only 10 5mmin stacked images processed in APP. But clearly the major issue is the blue ring. This is only present when using my 0.75x focal reducer on my RCT 8" F/8 OTA. What can I do to fix this problem? The reducer is useless for me at this present moment.

Below is my camera set up before it goes in the scope. in order left to right:

ASI533, M42-M48 Adapter ,T2-M48 16.5mm Extender, Astro Essentials 0.75x Reducer for StellaLyra / GSO Ritchey Chretien, Optlong CLS-CCD LP Filter

[vlaiv]

That looks like rather nasty reflection. I wonder if flat would deal with that (I doubt but worth a try).

Did you take flats?

[Adam J]

37 minutes ago, Quetzalcoatl72 said:

This is clearly a terrible image. Mainly because of the bad seeing being middle of june and only 10 5mmin stacked images processed in APP. But clearly the major issue is the blue ring. This is only present when using my 0.75x focal reducer on my RCT 8" F/8 OTA. What can I do to fix this problem? The reducer is useless for me at this present moment.

 

Below is my camera set up before it goes in the scope. in order left to right:

ASI533, M42-M48 Adapter ,T2-M48 16.5mm Extender, Astro Essentials 0.75x Reducer for StellaLyra / GSO Ritchey Chretien, Optlong CLS-CCD LP Filter

That is a reflection of some sort probably between the focal reducer and the filter. Could be a poorly applied AR coating on either component. How old is the reducer? 

[Quetzalcoatl72]

33 minutes ago, vlaiv said:

That looks like rather nasty reflection. I wonder if flat would deal with that (I doubt but worth a try).

Did you take flats?

No but I have a feeling if I used a Barlow lens I'd get the similar results. Reflections can't have been from an external source however, When I was taking darks the next day(not added to this image) I could see similar rings on my darks which is literally impossible right?

[Quetzalcoatl72]

3 minutes ago, Adam J said:

That is a reflection of some sort probably between the focal reducer and the filter. Could be a poorly applied AR coating on either component. How old is the reducer? 

I only just got it brand new from FLO a few months ago used once with my DSLR never had this problem

[vlaiv]

1 minute ago, Quetzalcoatl72 said:

When I was taking darks the next day(not added to this image) I could see similar rings on my darks which is literally impossible right?

That actually suggests a light leak of sorts.

What do you use to cover your scope? Light leak can come from back side - but also from front side. If you have plastic scope cover - that won't stop IR radiation from getting in. Most people add aluminum foil in that case.

[Quetzalcoatl72]

Heres a stacked image with my dslr and reducer, if it's a leak I would be from the asi533 however that's not the case without the reducer. Looks like I'm going to have to so some choice of elimination. Sadly AP is impossible atm, I get one hour of darkness for another month or 2. I do not use covers of any kind, can you give me an example?

[vlaiv]

2 minutes ago, Quetzalcoatl72 said:

I do not use covers of any kind, can you give me an example?

How do you take your darks? You have to put some sort of cover on the front of the scope?

Here is for example solution from one member here:

But light leaks can happen in different places - if you have extension tubes or even at scope seams - here is another case of light leak handling from CloudyNights forum:

[vlaiv]

8 minutes ago, Quetzalcoatl72 said:

Heres a stacked image with my dslr and reducer, if it's a leak I would be from the asi533 however that's not the case without the reducer.

I just checked ASI533 has just plain AR coated window - that means it is sensitive in IR part of the spectrum. DSLR is not.

This could mean that problem is related to focal reducer - but it might be that it is not. It could be simple IR leak that just started to show for a different reason. What has changed in your setup or environment recently?

[Quetzalcoatl72]

13 minutes ago, vlaiv said:

I just checked ASI533 has just plain AR coated window - that means it is sensitive in IR part of the spectrum. DSLR is not.

This could mean that problem is related to focal reducer - but it might be that it is not. It could be simple IR leak that just started to show for a different reason. What has changed in your setup or environment recently?

I just put the lens cap over when doing darks, and a hoodie or something draped over the top. I do remember putting a cloth over the setup shown in that picture and that took away one of the light rings in the darks, but one remained that I didn't get rid of, I could give it another go later to locate the light. Maybe I can figure it out during the day? as I wont be setting up for while. There's been no change other than lighter nights, and this was the first time setting up the asi/focal reducer combo.

[vlaiv]

9 minutes ago, Quetzalcoatl72 said:

Maybe I can figure it out during the day?

If you can make your darks light leak proof during the day - that will certainly do the trick at night.

[PadrePeace]

I’m going to take a wild shot at an IR source given that you had a ring even on your darks. It’s been really  hot these past few weeks. Could it be that your sensor is picking up a warm spot or structure within your optical train? I know this sounds whacky but given Vlad’s observations on the lack of IR coating on the sensor window is it likely that given the multiple mirrors in that RC this might be the IR source?

Might be worth adding as IR filter right in front of the sensor. 

[Adam J]

4 hours ago, vlaiv said:

That actually suggests a light leak of sorts.

What do you use to cover your scope? Light leak can come from back side - but also from front side. If you have plastic scope cover - that won't stop IR radiation from getting in. Most people add aluminum foil in that case.

Except the cls CCD should block IR. 

[vlaiv]

6 hours ago, Adam J said:

Except the cls CCD should block IR. 

Indeed it should - but I would not be surprised if it actually does not.

There have been examples before where filters that should not pass IR - actually do pass IR part of spectrum.

[Quetzalcoatl72]

20 hours ago, PadrePeace said:

I’m going to take a wild shot at an IR source given that you had a ring even on your darks. It’s been really  hot these past few weeks. Could it be that your sensor is picking up a warm spot or structure within your optical train? I know this sounds whacky but given Vlad’s observations on the lack of IR coating on the sensor window is it likely that given the multiple mirrors in that RC this might be the IR source?

Might be worth adding as IR filter right in front of the sensor. 

How many filters can you actually add to the camera without the image getting weird? in what order would the ir filter go with my Optlong LP and reducer/or/barlow

[PadrePeace]

I have the ASI224 and 294 and both accept a 1.25” IR cut filter right in front of the sensor. There’s a step down adaptor ring that comes with the camera to allow for this which screws inside your first adaptor next to your camera judging by the image you posted. 
 

Remember it’s a bit of a punt idea so if you don’t have a cut filter already might be worth borrowing one or get an SVBony IR cut filter off of EBay for £12. 

Edited June 17, 2021 by PadrePeace