25 replies to this topic

[dengar169]

Recently became the owner of a Sharpstar 150HNT scope. I've taken it out a couple of times so far and consistently get this circular gradient in my stacked/stretched images. I've attached starless example with only Graxpert used in Pixinsight. I've done 2 separate stacks, one with calibration frames and another without. It seems the circle is being caused by the subs themselves. I'm using a ZWO ASI2400MC-P which is a full frame sensor. Is this because the sensor is too big for the scope's image circle? Let's ignore my poorly collimated stars

 

 

Edited by dengar169, 30 October 2024 - 11:32 PM.

[DeepSky Di]

Please attach the images.

[dengar169]

Rookie mistake. Just edited to attach

[gsaramet]

Recently became the owner of a Sharpstar 150HNT scope. I've taken it out a couple of times so far and consistently get this circular gradient in my stacked/stretched images. I've attached starless example with only Graxpert used in Pixinsight. I've done 2 separate stacks, one with calibration frames and another without. It seems the circle is being caused by the subs themselves. I'm using a ZWO ASI2400MC-P which is a full frame sensor. Is this because the sensor is too big for the scope's image circle? Let's ignore my poorly collimated stars

 

Hello!

 

Can't see much useful in that image. However, a very simple answer to your question should lie within your flats. If instead of vignetting you have black outside that circle, it's the sensor size. Also, in that area, you won't see stars at all (well, mostly) in your lights. 

[dengar169]

Hello!

 

Can't see much useful in that image. However, a very simple answer to your question should lie within your flats. If instead of vignetting you have black outside that circle, it's the sensor size. Also, in that area, you won't see stars at all (well, mostly) in your lights. 

Sorry, I wasn't able to attach the star version. There are stars appearing outside of the circle. I did 2 separate stacks of this, 1 with calibration frames (flats, darks, etc.), and another with just the light frames. The circle shows up in both.

 

Here is the version including the stars:

 

[gsaramet]

I think it can be safely said that it's not the circle of illumination. 

 

Now, there are two things you can do. One is to bring the tube in a dark room, put one or two strong led flashlights inside and put the cap on. If you see light coming out, you need to fix that. It _could_ be light coming around the focuser drawtube. I had it in my newt. A cut sock will solve the issue. It could be light around the focuser itself. Could be coming from the back end of the scope. Just test it. 

 

The second is to share one of each types of frames in order for people to analyze: one bias (or dark flat), one dark, one flat, one light. Also describe how you are taking the flats. 

 

Cheers!

[vidrazor]

If you're using any extension rings or tubes, examine them and see if they're anodized. They could cause internal reflections like that if so. I've had to paint the inside of all my extension rings/tubes with flat black paint because they're were shiny anodized surfaces. Look for any shiny anodized surfaces.

Attached Thumbnails

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[dengar169]

Thank you both! I will test for light leaks and will also look for possible reflection issues in my image train. I'm using a Blue Fireball 360 Camera Angle Adjustor  on the focuser and am thinking it may be the cause of this problem. I have the same rotator on my Edge 8 but am not experiencing similar issues. Sounds like I have some testing to do. 

[vidrazor]

Thank you both! I will test for light leaks and will also look for possible reflection issues in my image train. I'm using a Blue Fireball 360 Camera Angle Adjustor  on the focuser and am thinking it may be the cause of this problem. I have the same rotator on my Edge 8 but am not experiencing similar issues. Sounds like I have some testing to do. 

Yes! I had to paint the inside of my 48mm and 42mm Blue Fireball 360 Camera Angle Adjusters, along with everything else in the chain. I used Rust-Oleum Flat Black Protective Enamel. Do not use water-based paints.

[dengar169]

Yes! I had to paint the inside of my 48mm and 42mm Blue Fireball 360 Camera Angle Adjusters, along with everything else in the chain. I used Rust-Oleum Flat Black Protective Enamel. Do not use water-based paints.

To Home Depot I go

[tosjduenfs]

I dealt with this issue for many years with my newts. I covered every crack and hole in the telescopes to no avail.  Eventually I took the imaging train off and capped it and started taking exposures while holding a flashlight in different orientations around the camera/filterwheel/OAG/coma corrector.  It turned out I had a light leak between the coma corrector and OAG, a threaded connection!  I would try the more obvious places first but if the issue persists make sure you check those bolted and threaded connections.

Edited by tosjduenfs, 31 October 2024 - 08:49 AM.

[unimatrix0]

Thank you both! I will test for light leaks and will also look for possible reflection issues in my image train. I'm using a Blue Fireball 360 Camera Angle Adjustor  on the focuser and am thinking it may be the cause of this problem. I have the same rotator on my Edge 8 but am not experiencing similar issues. Sounds like I have some testing to do. 

Since we are talking about a Newtonians, which are famous light strainers and they will include all light captured into your images, whether that's from a DSO or a porch light. 

 

Do a test at the same spot you image with a black cloth wrapped around the focuser part.  Now do a few without. Do as long as your subs are, also slew around the scope and do more test shots. 

 

 

Also the movement of your telescope throughout the night following the DSO, is there any point where a light shines on your telescope? 

 

If there is a light shining on your telescope from anywhere, there is a good chance that you got a light leak around the focuser. 

 

It could also be the back of the rear mirror. You're looking for a circle shaped light leak, so it could be around the rear mirror too. Just a guess. 

Edited by unimatrix0, 31 October 2024 - 09:03 AM.

[dengar169]

Thank you both. I have some homework to do now on this. I now suspect it is caused around the imaging train and/or focuser. I'm going to start there. But to Unimatrix' point, I'm also going to be running tests around the entire OTA for light leaks. I'll probably start using a black shower cap at the back end to cover the primary mirror and find a way to cover the focuser as well.

 

I dealt with this issue for many years with my newts. I covered every crack and hole in the telescopes to no avail.  Eventually I took the imaging train off and capped it and started taking exposures while holding a flashlight in different orientations around the camera/filterwheel/OAG/coma corrector.  It turned out I had a light leak between the coma corrector and OAG, a threaded connection!  I would try the more obvious places first but if the issue persists make sure you check those bolted and threaded connections.

 

 

Since we are talking about a Newtonians, which are famous light strainers and they will include all light captured into your images, whether that's from a DSO or a porch light. 

 

Do a test at the same spot you image with a black cloth wrapped around the focuser part.  Now do a few without. Do as long as your subs are, also slew around the scope and do more test shots. 

 

 

Also the movement of your telescope throughout the night following the DSO, is there any point where a light shines on your telescope? 

 

If there is a light shining on your telescope from anywhere, there is a good chance that you got a light leak around the focuser. 

 

It could also be the back of the rear mirror. You're looking for a circle shaped light leak, so it could be around the rear mirror too. Just a guess. 

[Oort Cloud]

I've never seen a light leak that perfect, but I also haven't had a lot of leaks to deal with either. The fact that it is perfectly round screams "reflection".

[dengar169]

I've never seen a light leak that perfect, but I also haven't had a lot of leaks to deal with either. The fact that it is perfectly round screams "reflection".

I was leaning towards reflection as well for this very reason. I suspect it's my rotator. Going to start there because I'm really not wanting to start flocking the edges of my secondary mirror or something else on the OTA 

[Oort Cloud]

I was leaning towards reflection as well for this very reason. I suspect it's my rotator. Going to start there because I'm really not wanting to start flocking the edges of my secondary mirror or something else on the OTA

I have used plenty of extensions, and most of them do not have a matte surface inside. I've only gotten something like this on my C6, and only when using the reducer.

So I'm a bit hesitant to think its extension tubes doing it, but I also don't own any Newts yet, so I'm admittedly not the best person to be speaking on this topic.

That said, I'll sit back and see what others say and follow along to see how you resolve it, so I can use that knowledge when I finally have one of my own.

[unimatrix0]

 

ZWO ASI2400MC-P which is a full frame sensor.

Quick question-  Are you using any filters and if you are, how far is it from the camera? 

[vidrazor]

To Home Depot I go

Wait a day or two for the paint to fully dry before using. I had a small fan adding some airflow to help along.
 

[dengar169]

Quick question-  Are you using any filters and if you are, how far is it from the camera? 

Yes, I'm using the ZWO Filter drawer installed right up to the camera plate. 

[Oort Cloud]

Try shooting with no filter. Maybe even no drawer, with any openings covered to keep light out.

[dengar169]

I have used plenty of extensions, and most of them do not have a matte surface inside. I've only gotten something like this on my C6, and only when using the reducer.

So I'm a bit hesitant to think its extension tubes doing it, but I also don't own any Newts yet, so I'm admittedly not the best person to be speaking on this topic.

That said, I'll sit back and see what others say and follow along to see how you resolve it, so I can use that knowledge when I finally have one of my own.

To your point, I’ve never had this issue with any other scope. I also use extension tubes in those. My, very beginner, assumption is because of the faster optics of the newt (shrug). That said, vidrazor has used the same rotator I have and ran into an issue with reflections so it’s definitely a great starting point. I’m taking everyone’s suggestions and will try a combination of all of them. 

[DeepSky Di]

I had rings like this in SCT images when I used an illuminated flat panel (Amazon tracing panel) with no white t-shirt. White t-shirt over the flat panel fixed it. 

[dengar169]

Welp nothing fixed this issue. Painted the inside of my extension tubes, tested for light leaks, etc. I'm at a loss. Is it possible for this issue to be caused by poor collimation of the secondary mirror?

[jonnybravo0311]

Have you tried a mirror mask?

[dengar169]

Have you tried a mirror mask?

I haven't because I've been worried about screwing up the mirror. But, it may have to be my next step.