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Halo's around dimmer stars

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#1 rishigarrod

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Posted 10 November 2019 - 06:26 PM

I have just added a flattner to my Esprit 100. I believe I have accurately setup the back focus.

I am using a ZWO ASI294 pro OSC camera. The example is a 180 second exposure with unity gain (120) which has been de-bayered.

 

When I zoom in the dimmer stars have a bright centre and a dim halo. I set the focus with a bahtinov mask.

 

Any idea's what causes this?

 

PixInsight_1_8_8.jpg



#2 WebFoot

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Posted 11 November 2019 - 01:17 AM

WAG--That looks like reflections, and the reflections are off something that's not orthogonal to the light path.  I'd look at the flattener, obviously, if this only started happening after you added the flattener.

 

Mark



#3 rishigarrod

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Posted 11 November 2019 - 01:46 AM

Thanks. I did have an adaptor made up to connect the scope to the flattner. Its only 8mm but it is still metal (silver) coloured.

Could that cause reflections?



#4 Tapio

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Posted 11 November 2019 - 01:47 AM

Is this crop?
I would also test reducer camera distance.
The theoretical optimal distance is not always practical optimal distance.

#5 rishigarrod

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Posted 11 November 2019 - 11:44 AM

Yes this is cropped and zoomed. Looking at the photo with no zoom it looks OK but as as I start pixel peeping I see this result.

 

i also think it maybe the distance between the flattner (no reduction) and the camera. Is there an easy way to test rather than having to wait for a clear night?



#6 WebFoot

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Posted 11 November 2019 - 02:10 PM

Thanks. I did have an adaptor made up to connect the scope to the flattner. Its only 8mm but it is still metal (silver) coloured.

Could that cause reflections?

The "reflections" of which I wrote are when a glass surface does not have sufficient coatings, and some of the light bounces around inside the glass, between the two surfaces, before eventually getting to the chip.  

If this only started happening after you put the flattener in, I would strongly suspect the flattener.



#7 rishigarrod

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Posted 11 November 2019 - 04:16 PM

The "reflections" of which I wrote are when a glass surface does not have sufficient coatings, and some of the light bounces around inside the glass, between the two surfaces, before eventually getting to the chip.  

If this only started happening after you put the flattener in, I would strongly suspect the flattener.

It is a new SkyWatcher flattner that is designed specifically for the Esprit 100.

I took many foto’s without the flattner and I did not see this problem. I hope it’s a back focus issue because at least I can fix that. 
 

Does anyone know a good way to test this. An artificial star?



#8 Monkeybird747

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Posted 11 November 2019 - 04:46 PM

Thanks. I did have an adaptor made up to connect the scope to the flattner. Its only 8mm but it is still metal (silver) coloured.

Could that cause reflections?

You have a shiny silver adapter in your image train? If it is silver on the inside that could very likely be your problem. If your flattener was not spaced correctly you'd notice it on the edges and corner of the frame as misshapen stars. Get some flat cammo spray paint from your favorite big box store, or a tube of chalkboard paint from your favorite hobby store and flock the inside of that adapter. You don't want anything shiny at all in your image train. Not even shiny black anodized stuff.

 

Post up a full res image unedited and we should be able to tell if your flattener is working. But as mentioned by WebFoot, this looks like a reflection problem, not a spacing problem.



#9 rishigarrod

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Posted 11 November 2019 - 04:59 PM

My local shop had to make up an adaptor for me as the flattner came with an EOS adaptor but not a screw adaptor for a non DSLR camera. On the ESPRIT 100 you need a 66mm adaptor which is a format that is not readily available (even from Skywatcher!). This is 'naked' metal. I will make the inside matt black as you suggest to at least eliminate it as a cause and who knows maybe fix it.

 

I have put un-edited version and one that is debayered on dropbox.

 

 https://www.dropbox.com/s/c5l2bzpg6q31wk5/IC%201396_Light_027.fit?dl=0

https://www.dropbox....27_RGB.fit?dl=0


Edited by rishigarrod, 11 November 2019 - 05:14 PM.


#10 Monkeybird747

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Posted 11 November 2019 - 08:18 PM

My local shop had to make up an adaptor for me as the flattner came with an EOS adaptor but not a screw adaptor for a non DSLR camera. On the ESPRIT 100 you need a 66mm adaptor which is a format that is not readily available (even from Skywatcher!). This is 'naked' metal. I will make the inside matt black as you suggest to at least eliminate it as a cause and who knows maybe fix it.

 

I have put un-edited version and one that is debayered on dropbox.

 

 https://www.dropbox.com/s/c5l2bzpg6q31wk5/IC%201396_Light_027.fit?dl=0

https://www.dropbox....27_RGB.fit?dl=0

Those stars are pretty out of focus, which makes it hard to tell whats going on. Could even be contributing to the issue, but it does look very much like a reflection problem. As for the flattener effectiveness, again hard to tell with an out of focus image, but I don't see elongated stars. Perhaps a small amount of horizontal tilt, but hard to say. Flock that adapter and get the best focus you possibly can and lets have another look. I'll just say for now spacing does not seem to be the culprit.



#11 rishigarrod

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Posted 12 November 2019 - 04:19 AM

Thanks for the feedback. Chalkboard paint is on its way. 
 

I agree that it looks like a focus issue too but I don’t understand how it can be so far off when using a bathinov mask. 
 



#12 rishigarrod

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Posted 12 November 2019 - 01:35 PM

When I look at this I think you guys got it right.

Paint arrives tomorrow.

 

IMG 7810

 



#13 Monkeybird747

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Posted 12 November 2019 - 01:43 PM

I'd go ahead and carefully dab some of that paint on those shiny screw heads while you're at it. No idea why they use shiny silver screws on the camera face, but I painted the ones on my 183.



#14 rishigarrod

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Posted 12 November 2019 - 02:58 PM

Agree. I only really saw the screws when I took the photo.




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