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Old 11-12-2010, 05:59 PM
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Hyperstar reflections

I wonder whether anyone else has encountered these reflection patterns in their imaging (Hyperstar or otherwise). I am using a QHY8 OSC with the recommended hyperstar adapter on top of an EdgeHD 1400. The QHY8 has the internal IR filter still in place.
The pattern is not identical from one image to another but has strong similarities all the same. Here are some crops from 2 images taken the same night.
Peter
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Old 11-12-2010, 06:07 PM
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Are they in the same place in all the images Peter?

Pretty though
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Old 11-12-2010, 06:29 PM
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Are they in the same place in all the images Peter?

Pretty though
Hi Paul. I've just been checking the individual subs and the reflections are identical shapes and in identical places in each sub BUT while all the Horsehead subs have the reflection in the same location, all the M42/43 images while having their very similar reflection in the same shape and place in each sub, they are, curiously, on the horizontal opposite side to those in the Horse subs - a 180 degree horizontal flip but, as you'll appreciate, hardly any real OTA movement between the 2. I just received a nice new Astrozap heater/dewshield today that I didn't have when I took these images so I'll try again when the weather allows and see what is happening here.
In the meanwhile, your thoughts very welcome.
Peter
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Old 11-12-2010, 06:48 PM
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whatever is creating it looks like its moving.
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Old 11-12-2010, 07:18 PM
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Originally Posted by [1ponders] View Post
whatever is creating it looks like its moving.
You don't have to look far to find proof of alien life do you. These are obviously signs from an intelligent extraterrestrial intelligence sent to try to establish the presence of sentient beings. How should I respond?
Peter
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Old 11-12-2010, 07:22 PM
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Obvious Pete. shine your green laser through your scope and send your own photonic message back
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Old 11-12-2010, 11:38 PM
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That would be light from Zeta Orionis. Probably not much you could do about it if there is such a bright star close by.
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Old 12-12-2010, 01:47 AM
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Hi Peter,
You can start to eliminate things by removing or replacing bits.
To check if the the nose/filter of the QHY-8 camera is the cause, i recommend you remove the filter/nose and replace it with just a spacer of the same length (So you can focus). BUT, and i mean BUT, DO NOT CONNECT the TEC power cable. This way you wont fog up and wet the internals. With the TEC off, you can take the same image, and see if the reflections still there. If not, theres your problem, else, well, you need to see..

Theo
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Old 12-12-2010, 04:33 AM
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Thanks Andrew, Theo.
I'll see if I can devise a repeatable process of elimination. I'm not over-confident that bright-star reflections would cause this sort of artifact Andrew. I've seen what you are referring to before when they appear either as great elliptical halos (seen in an old GSO Ritchey-Chretien) or a strong rays coming from off-screen - usually Alnitak when doing a Horsehead etc. But these are unlike that. They also have a distinctly blue colour. That makes me think it is a reflection coming off a coated glass surface somewhere inside the optical train itself rather than from any external starlight-based source.

Theo, for the purpose of this experiment, I will try some out-of-focus images first. If the reflection remains and has the same fairly well-defined linearity and colour while the rest is out-of-focus, it will tell me that the source is probably the inside surface of the the IR filter. I'll then remove that filter and repeat the process with and without a spacer. I note what you have said about the power to the cooler. The thing that worries me at the moment is what to do if the culprit is in fact that nosepiece filter.

Just to add some confusion, here is a third image from the same session - it's a LMC widefield and it shows no sign of that artifact. SO maybe Andrew is right.

Peter
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Old 12-12-2010, 08:16 AM
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Quote:
Originally Posted by Gama View Post
Hi Peter,
You can start to eliminate things by removing or replacing bits.
To check if the the nose/filter of the QHY-8 camera is the cause, i recommend you remove the filter/nose and replace it with just a spacer of the same length (So you can focus). BUT, and i mean BUT, DO NOT CONNECT the TEC power cable. This way you wont fog up and wet the internals. With the TEC off, you can take the same image, and see if the reflections still there. If not, theres your problem, else, well, you need to see..

Theo
Those are not camera reflections. I use no nosepiece glass and they show with other camera types as well. I think they're caused by the schmidt profile on the corrector. Not much you can do about them but process them out.
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Old 12-12-2010, 09:06 AM
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You can see the same pattern from the reflection in the image of venus on this webpage in a schmidt camera.

In terms of a soluition you could try shorter exposures (which probably defeats the purpose of going deep on a dim object) or simply target objects without bright stars close by.
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Old 12-12-2010, 10:45 AM
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Well, I'll be stuffed. So it is. Andrew, thanks for that link. I'm convinced. And Marc also, you're both right. And the solution is - stay away from over-bright stars or do really short exposures. Hmmm. Not much of an option. So it'll have to be a post-processing thing. New skills coming up.
Now I know this I don't have to bother horsing about with the IR filter - but Marc, why did you remove yours and if you use it on a hyperstar, how do you maintain the separation distance?
Peter
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Old 12-12-2010, 02:37 PM
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I've been doing some reading and it seems Andrew and Marc are right. Apparently, light is reflected back from the corrector plate causing these ghosts. One thing that might be worth trying is to tilt the corrector plate slightly so that ghosts are outside the field - not sure what effect that will have on image quality though.

Anyway, here is the reflection I see in my hyperstar from Zeta Orionis.

Terry
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Old 12-12-2010, 02:43 PM
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I've been doing some reading and it seems Andrew and Marc are right. Apparently, light is reflected back from the corrector plate causing these ghosts. One thing that might be worth trying is to tilt the corrector plate slightly so that ghosts are outside the field - not sure what effect that will have on image quality though.

Anyway, here is the reflection I see in my hyperstar from Zeta Orionis.

Terry
Yep. Now it seems we need to find a way to make a defect into a virtue - Terry yours is nicely symmetrical - I wonder if there is any correlation with alignment/collimation.
Peter
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Old 12-12-2010, 03:08 PM
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So would getting the corrector coated with an antireflective coating in the inside work? or would this be also due to the edges of the lenses in the hyperstar?
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Old 12-12-2010, 03:16 PM
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So would getting the corrector coated with an antireflective coating in the inside work? or would this be also due to the edges of the lenses in the hyperstar?
The easy fix for this is to shoot half your subs on the other side of the meridian then reject the halos. It's very easy to do. PS5 has also a cool content aware spot healing brush that can be used to get rif of internal halos. I'm plagued with halos with my MPCC and I just process them out now, It's just one more step. I just got used to it.
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Old 12-12-2010, 03:34 PM
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The easy fix for this is to shoot half your subs on the other side of the meridian then reject the halos. It's very easy to do. PS5 has also a cool content aware spot healing brush that can be used to get rif of internal halos. I'm plagued with halos with my MPCC and I just process them out now, It's just one more step. I just got used to it.
so you use a MPCC with a hyperstar?

you wouldnt like to do a small tutorial on that Marc?
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Old 12-12-2010, 03:42 PM
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so you use a MPCC with a hyperstar?

you wouldnt like to do a small tutorial on that Marc?
No I use a MPCC with my newt and I get internal reflections inside the MPCC glass. I was just saying halos and reflections are something you learn to live with and process out. Same goes for the hyperstar reflections. Yeah I should put something together and post it. Will do.

The basic idea is to offset the field or rotate it 180 degrees (in the case of a meridian flip). As long as the halos don't fall in the same spots then it's just a matter of making a difference layer until you get a valid reference frame. Then you can use it to reject the halos in your other subs.
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Old 12-12-2010, 04:11 PM
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No I use a MPCC with my newt and I get internal reflections inside the MPCC glass. I was just saying halos and reflections are something you learn to live with and process out. Same goes for the hyperstar reflections. Yeah I should put something together and post it. Will do.

The basic idea is to offset the field or rotate it 180 degrees (in the case of a meridian flip). As long as the halos don't fall in the same spots then it's just a matter of making a difference layer until you get a valid reference frame. Then you can use it to reject the halos in your other subs.
A tute on this would be terrific Marc.
Peter
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Old 12-12-2010, 04:14 PM
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A tute on this would be terrific Marc.
Peter
Will do. I just have to tidy up everything and put it together as the process is different depending of the type of picture you're working on and the type and size of what you're trying to remove. It's not a 'one fit all' model but the concept can be re-used and extended I guess.
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