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Some of my stars are donut shaped with a refractor

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#1 chvvkumar

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Posted 23 July 2023 - 02:41 PM

I noticed some of my stars are this donut shaped. This happens across two targets I tried. I have so far tried the following:

 

1. Re-run autofocus (though I am not sure if this is the issue since other stars are in focus)

2. Physically tighten up the imaging train so there is no unnoticed slack

 

I have uploaded my stacked image here:

 

https://drive.google...?usp=drive_link

 

I see this with the individual image frames as well (I also uploaded the individual sub to google drive).

 

Any idea what could be causing this?

 

My equipment:

 

80mm Doublet refractor, ASI533 OSC, ZWO Dualband filter, Auto Focus using ZWO EAF in NINA, 

Polar alignment was within <1 arc second and PHD2 RMS error was ~0.6

 

preview.png



#2 BucketDave

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Posted 23 July 2023 - 02:49 PM

Might be a reflection within the doublet objective. Have you tried to separate the three channels? If its a double-reflection within the objective, it will probably be most visible in the blue or green channel.
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#3 AstroCub

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Posted 23 July 2023 - 03:01 PM

I noticed some of my stars are this donut shaped. This happens across two targets I tried. I have so far tried the following:

 

1. Re-run autofocus (though I am not sure if this is the issue since other stars are in focus)

2. Physically tighten up the imaging train so there is no unnoticed slack

 

I have uploaded my stacked image here:

 

https://drive.google...?usp=drive_link

 

I see this with the individual image frames as well (I also uploaded the individual sub to google drive).

 

Any idea what could be causing this?

 

My equipment:

 

80mm Doublet refractor, ASI533 OSC, ZWO Dualband filter, Auto Focus using ZWO EAF in NINA, 

Polar alignment was within <1 arc second and PHD2 RMS error was ~0.6

 

attachicon.gif preview.png

I test all my focussing with a Bahtinov, have you tried that?

 

If this is a new issue for you, it could be down to high level smoke in the atmosphere.

Even when it has looked clear lately there has still been smoke around and I have noticed it has led to some bloated stars on my RASA. I know you're using a refractor, but it maybe be possible you're getting affected by the smoke, too. Just a thought.  

 

Best wishes

 

Siouxsie 


Edited by AstroCub, 23 July 2023 - 03:30 PM.

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#4 chvvkumar

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Posted 23 July 2023 - 03:08 PM

Might be a reflection within the doublet objective. Have you tried to separate the three channels? If its a double-reflection within the objective, it will probably be most visible in the blue or green channel.

I just did and it seems to be similar across channels

2023-07-23_15-02-36.jpg

 

 

I test all my focussing with a Bahtinov, have you tried that?

 

If this is a new issue for you, it could be down to high level smoke in the atmoshere. Even when it has looked clear lately there has still been smoke around and I have noticed it has led to some bloated stars on my RASA. I know you're using a refractor, but it maybe be possible you're getting affected by the smoke, too. Just a thought.  

Very well could be, I did have some smoke and high clouds. I was in Nebraska for NSP for this image. My Barnard 150 from the previous night turned out OK which was why it was puzzling. The Barnard picture is posted in the following reply to this reply.



#5 chvvkumar

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Posted 23 July 2023 - 03:08 PM

I test all my focussing with a Bahtinov, have you tried that?

 

If this is a new issue for you, it could be down to high level smoke in the atmoshere. Even when it has looked clear lately there has still been smoke around and I have noticed it has led to some bloated stars on my RASA. I know you're using a refractor, but it maybe be possible you're getting affected by the smoke, too. Just a thought.  

Barnard 150

 

masterLight_BIN_1_3008x3008_EXPOSURE_180_00s_FILTER_IR_RGB_autocrop_integration_autocrop_ABE.jpg


Edited by chvvkumar, 23 July 2023 - 03:13 PM.

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#6 Midnight Dan

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Posted 23 July 2023 - 03:21 PM

Looks like halos caused by the duo-band filter.

 

-Dan


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#7 BucketDave

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Posted 23 July 2023 - 03:46 PM

I just ran the original image and that of Barnard 150 through Tenmon.  The original image is 0.059% saturated in the green channel (ought to be around 0.003%) where-as the image of Barnard 150 is 0.005% saturated (so about right).  What exposures and gain did you use?


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#8 Bigeye1988

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Posted 23 July 2023 - 03:51 PM

I vote halo from the filter. I believe there's a thread here on the subject. Some filters have more halo than others, that sort of discussion.
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#9 chvvkumar

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Posted 23 July 2023 - 04:03 PM

I just ran the original image and that of Barnard 150 through Tenmon.  The original image is 0.059% saturated in the green channel (ought to be around 0.003%) where-as the image of Barnard 150 is 0.005% saturated (so about right).  What exposures and gain did you use?

For Eagle:

150 second exposure, 100 gain and 70 offset with ZWO DuoBand filter

 

For Barnard 150:

180 second exposure, 100 gain and 70 offset with ZWO IR/UV cut filter

 

Stacked image for Barnard 150 is uploaded here. The image I attached is a low quality JPEG to fit into the attachment size limit

https://drive.google...mYT?usp=sharing



#10 chvvkumar

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Posted 23 July 2023 - 04:05 PM



Looks like halos caused by the duo-band filter.

 

-Dan

 

 



I vote halo from the filter. I believe there's a thread here on the subject. Some filters have more halo than others, that sort of discussion.

I am not 100% on that. Here is a previous image with basically the same imaging train and the same filter. It does not show any such artifacts:

 

get.jpg?insecure



#11 Bigeye1988

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Posted 23 July 2023 - 05:16 PM

Halos aren't generally a problem. They're most evident around relatively bright stars.

#12 RogeZ

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Posted 23 July 2023 - 06:33 PM

A good combination of CA and filter halo, imho.

The heart image has the same halos but the tracking was compromised and therefore it blurred the halo.
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#13 chvvkumar

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Posted 23 July 2023 - 07:14 PM

A good combination of CA and filter halo, imho.

The heart image has the same halos but the tracking was compromised and therefore it blurred the halo.

Could very well be now I think about it. I recently switched to an OAG from my guide scope. For some reason, just doing that brought my PHD2 error from an average of 1-1.5 RMS down to 0.3-0.6. Do you think the improved guiding might be bringing out the flaws that were being masked by bad guiding before?


Edited by chvvkumar, 23 July 2023 - 07:14 PM.


#14 RogeZ

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Posted 23 July 2023 - 07:35 PM

Could very well be now I think about it. I recently switched to an OAG from my guide scope. For some reason, just doing that brought my PHD2 error from an average of 1-1.5 RMS down to 0.3-0.6. Do you think the improved guiding might be bringing out the flaws that were being masked by bad guiding before?


Absolutely. I think for the scope you are using the results are quite good but scopes not perfectly apo benefit from mono cameras.

#15 Midnight Dan

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Posted 24 July 2023 - 09:29 AM

 

 


I am not 100% on that. Here is a previous image with basically the same imaging train and the same filter. It does not show any such artifacts:

 

get.jpg?insecure

Here's a star in the lower left corner of that image:

 

Screenshot 2023-07-24 at 10.27.47 AM.jpg

 

Halos will only show on the brightest stars, and only on stars of certain colors.  The real test would be to take the same image as your first post, but without the filter.

 

-Dan


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#16 jml79

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Posted 24 July 2023 - 10:05 AM

Absolutely. I think for the scope you are using the results are quite good but scopes not perfectly apo benefit from mono cameras.

I have the bigger brother scope and yes, it will blue halo around bright stars. This is completely limited to the blue channel and doesn't appear in any other channels or when using NB filters. It is tame enough that an Astronomic L3 or slightly better/narrower blue filters (when shooting RGB with a mono camera) all but eliminate it.

 

If it is visible in all channels or when using a NB filter, then it is not a result of the scope being a doublet. The Iris photo on my astrobin is a Sony A6000 used with a SV503 scope and the Astronomik L3, very little blue halos.


Edited by jml79, 24 July 2023 - 10:07 AM.

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#17 chvvkumar

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Posted 31 August 2023 - 12:05 PM

An update, I was imaging NGC 7822 last night and the resulting image has this halo around one star. If this is caused by the filter, wouldn't it effect all similarly sized stars with similar brightness equally? I am wonderign why it is only showing up so prominantly on just ne star

 

 get.jpg?insecure



#18 sharkmelley

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Posted 31 August 2023 - 12:19 PM

An update, I was imaging NGC 7822 last night and the resulting image has this halo around one star. If this is caused by the filter, wouldn't it effect all similarly sized stars with similar brightness equally? I am wonderign why it is only showing up so prominantly on just ne star 

 

Certainly it's very prominent on one particular star but that's simply the way the image has been processed.  Looking at the full resolution image on Astrobin I can see many stars that are similarly affected.


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#19 chvvkumar

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Posted 31 August 2023 - 01:01 PM

Certainly it's very prominent on one particular star but that's simply the way the image has been processed.  Looking at the full resolution image on Astrobin I can see many stars that are similarly affected.

You are of course, correct. I was wondering why the donut only shows up on one star but not on others. The others have a more diffused halo Vs. thie one in the middle with a donut halo.

 

I can somewhat work with the diffused halo as I can shoot RGB stars with IR filter and blend them in. The donut stars make that a bit complicated.



#20 sharkmelley

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Posted 01 September 2023 - 01:29 AM

You are of course, correct. I was wondering why the donut only shows up on one star but not on others. 

The image has been non-linearly stretched.  This means that the relative brightnesses of the star core and halo appear different for different brightness stars.  




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