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Distortion/Reflections in My View

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#1 reedcbr55

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Posted 21 January 2013 - 01:09 AM

Guys, please forgive me as a noob if this is the wrong place for this but I couldn't find a subject that fit any better. I have just purchased a Celestron C6-SGT. I am using the diagonal together with the 25 mm and the 34 mm eyepiece. When viewing a bright star (Sirius, for example), the image looks fine as long as the star is centered. However if I slew slightly off center in any direction, I get an egg shape type halo/reflection of the star. I've included a drawing to illustrate. This occurs, regardless of environment (both warm & cold). If I view two bright stars in close proximity, if one is off center, it will produce this halo effect preventing clear viewing of the other star. Any ideas what may be causing this?

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#2 GlennLeDrew

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Posted 21 January 2013 - 04:27 AM

Does this reflection move at all when you move your eye? If not, we can rule out it being the result of light reflecting off your cornea.

Is the form of the reflection similar in both eyepieces? If so, the reflection most likely originates in or at least involves the scope's optics.

#3 Jon Isaacs

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Posted 21 January 2013 - 07:22 AM

Reed:

Hello and Welcome to Cloudy Nights... Very nice drawing... :goodjob:

What do you see when viewing more normal stars? How far off-axis do you need to be to get this effect? Do you have other eyepieces to try?

Jon

#4 reedcbr55

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Posted 21 January 2013 - 10:14 PM

Glenn: The reflection does not move when I move my eye. My wife sees it as well. It is the same in both eyepieces. Jon: When viewing progressively dimmer stars, the reflection eventually goes away.

I also have a Celestron C8 and I tried the same diagonal and eyepieces on it and I do not see the reflection/distortion.

Any ideas what the cause may be? Collimation?

#5 dpwoos

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Posted 22 January 2013 - 08:43 AM

I think you certainly ought to check alignment/collimation, given that there doesn't seem to be another ready explanation. Do you know how to collimate an SCT? If not, then I think you would be well served by learning how to do so, especially as you have two of them. Google it.

#6 GlennLeDrew

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Posted 22 January 2013 - 09:01 AM

I've seen a somewhat similar reflection which plagued another CN member with his C6 SCT when doing prime focus imaging. It manifested as an illuminated ring of narrow width, with the illumination source appearing on the ring. Unlike the egg-shaped appartion described here, it was pretty much circular.

I wonder if there is some aspect of the dimensioning of the optical system in this specific scope which leads to this type of internal reflection...

#7 JLovell

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Posted 22 January 2013 - 09:06 AM

Sounds to me that there is a surface inside the scope that needs to be painted black, flocked and/or baffled, but isn't. I think there are some internal reflections going on. Unless you are brave enough to take the scope apart and tackle painting or flocking, it may just be something you learn to live with as diffraction spikes from spider vanes are for us Newt owners. Before trying to take it apart, make sure you read up on instructions about how to safely do so.

#8 dpwoos

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Posted 22 January 2013 - 09:50 AM

In my (limited) experience, taking the corrector out of an SCT is not a big deal. The only thing that might not be obvious is the necessity of preserving the orientation of the corrector. I would go for it.

#9 Jon Isaacs

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Posted 22 January 2013 - 10:07 AM

In my (limited) experience, taking the corrector out of an SCT is not a big deal. The only thing that might not be obvious is the necessity of preserving the orientation of the corrector. I would go for it.


I have one rule when it comes to SCTs.. no matter what the question is:

Ask "Uncle" Mollise... he hangs out in the CATs and CASSes forum and he has seen it all...

Jon

#10 csrlice12

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Posted 22 January 2013 - 10:14 AM

Uncle Rod will know. He'll consult the Rebel Yell oracle--the bigger the problem, the more consultation will be needed.... :lol:

Yup, nobody knows CATs/Cass/SCTs like he does...

#11 Eddgie

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Posted 22 January 2013 - 11:06 AM

First, make sure there is not dew forming. Dew will give odd light in the field.

If the star still stays more or less sharp but you are seeing some glare in the field, the most common cause of this is light reflecting off of some bright surface.

There have been some cases of glare coming from unpainted areas in the baffle tube. The easiest way to see this is to remove the visual back and look in while someone shines a flashlight directly into the front of the scope and watching for any glare points.

If you don't see any, then inspect the inside of the visual back and the front of your diagonal for unpainted areas.

Try putting the eyepeiece directly into the visual back to see if the problem goes away. If it does, then it could be a diagonal problem.

Also, sometimes people with developing cateracts will have glare issues. Try using the other eye.

It sounds though like you are getting some kind of glare and this almost always coming from some unpainted surface and there have been a couple of C6s that had paint missing from the inside of the baffle tube. Inspect it carefully.

#12 panhard

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Posted 22 January 2013 - 02:11 PM

I also have a Celestron C8 and I tried the same diagonal and eyepieces on it and I do not see the reflection/distortion.

Reed tried it in another scope and the problem disappeared in that scope.

#13 Alfredo Beltran

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Posted 22 January 2013 - 08:46 PM

Hi

I also have a C6 that originally came as a NexStar 6SE and now rides on an iEQ45 mount. You can see images of the setup and those I've taken with it at the link on my signature.

This is a common problem in some C6 telescopes (mine has it also). In this thread you can see the solution:

http://www.cloudynig...3331861/Main...

It is just to flock the main baffle

Best regards,

Alfredo

#14 rmollise

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Posted 23 January 2013 - 07:36 AM

Your scope is fine. The SCT's naturally curved field will cause this effect due to field curvature and coma that are inherent in this design. If it bothers you, you can reduce it by using Celestron's f/6.3 reducer/corrector.

As for the "halo" business...that depends. It is not unusual to see a little of that around a bright object. The cause can be any number of things...a little dew...dirty eyepiece...your eyes...etc. Try a different eyepiece of similar focal length if possible and report back.

#15 reedcbr55

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Posted 23 January 2013 - 11:19 AM

Thanks Alfredo, I will look into that post

#16 reedcbr55

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Posted 23 January 2013 - 06:57 PM

Thanks Uncle Rod, I truly value your input and feel better now.






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