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Celestron C6 question

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#1 ilovecomets

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Posted 15 November 2012 - 06:26 AM

First off hello to everyone. Long time lurker here. Been enjoying reading these forums for years.

I recently bought a new Nexstar SE C6. Love the scope. The all sky alignment is fantastic. Makes it really easy for my wife or myself to use the scope. Yesterday I got my Celestron f/6.3 focal reducer. Everything I've heard on this forum prompted me to get it. Well when I installed it something very weird happened. I'm seeing arcs off any bright object in the eyepiece. It is very noticible. When I take it out, they go away...mostly. What I didn't notice before is that bright objects just off the eyepiece will sometimes cause smaller arcs in the field. But there arcs don't look the same as the ones I see its the reducer in. The reducer arcs are brighter, each star has one, there are usually two per star, and they're not smooth in appearance.

So I'm wondering:
1. Do I have a bad focal reducer?
2. Is there something wrong with my scope?

I've ordered a replacement reducer to see if that's the problem. I also tried a different diagonal and all my eyepieces, and it didn't make the problem go away with the reducer in. As for the problem I didn't notice before with off field light sources, it's a minor issue and probably not related or a big deal. I wasn't looking for it before and didn't see it.

What do you think I should do? If the next reducer shows the same problem, should I send the scope back for a replacement?

Thanks for your help.

#2 rmollise

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Posted 15 November 2012 - 07:39 AM

It is not unusual to see reflections off bright objects with the r/c. IOW "normal." I've never found them overly prominent unless you are on a very bright star or one is just out of the field.

#3 ilovecomets

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Posted 15 November 2012 - 09:56 AM

Hi Uncle Rod,

That's good to know. I've looked through a C8 with the same kind of reducer and didn't remember seeing this phenomenon. Then again I wasn't looking for it as well. If its normal I can live with it, and probably won't think much about it.

But just to be sure we're talking about the same thing, on Jupiter last night, and even some of the surrounding stars (4th magnitude) they had these weird arcs that filled up most of the eyepiece. It was most prominent in the 17 and 13 plossls and the Astro Tech Paradigm 18, 8, and 5. It's a new scope and didn't want to wind up with a lemon. But without the corrector in place I didn't see this artifact with any eyepiece. So it sounds like internal reflections off the corrector. This weekend I'm going to try a buddy's on the scope to rule out a problem with the flattener/reducer.

PS love your books

#4 mclewis1

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Posted 15 November 2012 - 03:11 PM

Something else to consider ... with the faster focal ratio when using the focal reducer the exit pupil of an eyepiece will be larger. You may be seeing more astigmatism from your own eyes when using the reducer than without out.

You might also try taking a careful look at the stars and comparing them between low and higher power eyepieces. All things being equal (same design of eyepiece, etc.) the lower power eyepieces should show more "arcs" if your eyes are introducing some astigmatism.

It is actually very common for an individual's eyes to introduce some optical aberration ... most folks usually don't notice it though. It's something the eyepiece manufactures are used to dealing with.

Something else to try when viewing with friends ... try out different eyepiece types/designs. Eye placement can sometimes make reflections and arcs less or more visible.

#5 ilovecomets

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Posted 15 November 2012 - 03:50 PM

Good suggestions. In this case the arcs I'm seeing are more than 50% of the field. I tried 8-10 eyepieces and they all showed the artifact irregardless of the magnification or exit pupil size. But it only appeared with the reducer in place. I'm trying out the other reducer tomorrow night. It's possible there's something wrong with the scope. I'm just hopeful that's not the case. Luckily the scope was decently collimated and didn't show many signs of poor optics.

#6 brettisley

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Posted 16 November 2012 - 12:49 PM

Long time lurker here as well. I recently decided to experiment with an SCT again after a not-so-great experience with a 12" LX200 that sent me on the refractor path years ago. I picked up a year-old C6 a couple of months ago and it has the same issue you describe. I experienced these arcs of light both with and without the focal reducer.

I believe that I've found the problem with mine and it is that the rear baffle tube that extends through the mirror into the scope is not well painted towards the front. As a test I cut a piece of Protostar flocking material and inserted into the baffle tube. Earlier this week I verified that the light arcs have disappeared both with and without the reducer.

At some point I suspect I will remove the corrector plate and re-paint the baffle tube, but it will be awhile before I have the time to dedicate to this project. Although I'm sure that I lose some light throughput due to the slightly reduced aperture of the baffle, it is fine for me at this time. I'm sure you could achieve a similar result with black construction paper. I owe thanks to this forum for this recommendation. I hope this helps.

#7 meade8r

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Posted 16 November 2012 - 02:20 PM

I had a C6 three years ago. It would show wide arcs when bright stars were near the edge of the view. The arcs would collapse as the object neared the center of view. Many others had reported this. I sent it back to Celestron. All they did was collimate it. The out-of box collimation was pretty good, but not perfect. Collimating seemed to help. Others reported the "paint problem" as mentioned above. You might check collimation first.

CB

#8 brettisley

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Posted 16 November 2012 - 03:18 PM

I also contacted Celestron about repair. In my case, the scope was considered out of warranty, since I am not the original owner - understandable. I was quoted $175 plus two way shipping and a 3-4 month lead time to evaluate the scope. When I asked if repairs would be made, the response was that they would clean, collimate and evaluate the scope. That didn't make me feel that the it was worth the money or time to return it.

#9 mclewis1

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Posted 16 November 2012 - 03:40 PM

My 2006 era black tubed C6 has about 3/4" of flocking material on the inside of the baffle tube. I can't remember ever seeing any unusual arcs visually ... but I can see the effect of the flocking not being perfectly installed with it's small gap between the edges. I have also seen some strange artifacts when imaging but they were only due to focal reducers or filters in the optical path.

#10 ilovecomets

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Posted 17 November 2012 - 10:30 AM

Well I did two tests last night. First I tried a second reducer, same problem. Then I tried both reducers on another C6. Same problem on that scope too. It looks to be internal reflections off the reducer causing brighter objects to show reflections. Neither scope showed the arcs on axis when the reducers were removed.

Without the reducers my scope showed the off axis arcs, the other C6 did not. It appears the reflection off my baffle are worse than the older C6. Shining a light down the baffle or from the front of the scope shows a uniform coating. It just looks like Synta isn't using a dark enough paint to minimize reflections. Down the road I may flock the baffle. For now I'll deal with reflections.

Thanks everyone for your suggestions. It helped track down what the issue is. If I knew this ahead of time, I may have went another direction. But honestly it's not that big of a deal for a $400 OTA.

#11 Eddgie

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Posted 17 November 2012 - 02:34 PM

Don't be fooled by the paint.

This is not to say that there isn't a problem, but I would say only if you see a place where the paint is missing.

The real interrior baffling is not the flat black paint, but the small ridges in the tube itself. These small ridges are mirco-baffles and carry most of the weight of reducing specular shine from shallow angle light that might reach the inside of the baffle.

If on the other hand, you do see a place where paint is missing, that is totally different.

It is very easy to check this though. Dureing the day, just pull the diagonal out and take off the front cover and point it to a bright light source. If you don't see any glint anywhere and the baffle walls look black from the back, than that is all that matters. Even if the paint does not look black from the front, that doesn't mean anything at all. Only what you see from the focal plane matters.

#12 MRNUTTY

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Posted 17 November 2012 - 07:04 PM

Just had my C6 out observing Jupiter. I've also seen the arc in this scope. It was very bright with jupiter in view. I see it with and without a Meade 6.3 FR in the visual train. I haven't looked inside the C6 lately. It looks like it could be a reflection in the baffle walls.

#13 orion61

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Posted 17 November 2012 - 08:28 PM

Question, are these Celestron FR's?
I dont have problems with mine. Are they the newer China reducers or the older MIJ?
I usually my Japanese one on my Orange tube C8 but have used it for my NX6se and never noticed any issues, they were tho designed for use with low power deep sky viewing.
Are these air spaced? or cemented?

#14 ilovecomets

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Posted 18 November 2012 - 06:30 AM

Mine is the Celestren reducer/corrector from Japan. The second one I tried was the China stamped model. I didn't notice a difference between the two.

On the C8, there hasn't been an issue. But on two different C6s the artifact was visible on anything bright off axis. Move the object to the center and it goes away. To my eyes it looked like an internal reflection issue.

#15 Jmel

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Posted 11 December 2012 - 02:44 PM

Any luck getting this to go away? I seem to have the same problem in my 5se OTA. It is very pronounced when I am taking photos. I am going to try to collimate, but it has been there for as long as I can remember.

#16 jrbarnett

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Posted 11 December 2012 - 10:02 PM

I see bright star arcing in my C6 and C90 to some degree. It seems to be glare caused by internal wall reflections or refraction by the edge of the corrector. I've been too lazy to blacken the corrector edge to see if it quells the unruliness. My C8 and C5 don't do it, though.

Regards,

Jim

#17 Chrispy

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Posted 11 December 2012 - 11:45 PM

Very new to SCT scopes, my 'new' 2nd hand C6 arrived yesterday!
Reading through the SCT threads, and borrowing a drawing that relates to the C6, I now have a clearer understanding of what I've bought.
Am I right in thinking the baffles you referring to are those that I've indicated in the drawing?
Is it supposed to be flocked on both surfaces?
"the top 1" of the central baffle refers to?

Thanks

Chris

Attached Files



#18 mclewis1

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Posted 12 December 2012 - 10:49 AM

Chris,

Try that file attachment again (nothing is present in your post).

In our discussions on the C6 the "flocking" (either paint or adhesive material) is on the inside of the baffle tube. The "top 1" refers to the inside area of the baffle tube farthest away from the primary mirror. Also note as Ed has mentioned above that while a bit of flat black paint helps the real reduction in reflected light inside the baffle tube comes from the small ridges machined into the inside wall.

Here is a link to an older thread with pictures of some of what has been discussed in the posts above ... http://www.cloudynig...3331861/Main...

#19 Chrispy

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Posted 12 December 2012 - 03:39 PM

Thanks Mark, I've managed to attach the drawing this time.
I now understand you are talking about the baffle tube, whereas I was referring to the secondary casing/baffle.
Cheers
Chris

#20 Jmel

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Posted 12 December 2012 - 08:41 PM

I closely studied my primary baffle tube, and I have to say that I don't see much difference... the baffling seems to go all the way to the edge. My issue may be in the secondary baffle...

#21 mclewis1

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Posted 12 December 2012 - 08:57 PM

Chris,

I've never looked through a scope that's had that flocking done so I can't offer any personal experience but from what I've read around here adding flocking where you indicated in the secondary baffle is probably the most beneficial addition to an SCT, particularly older ones.

#22 Jmel

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Posted 12 December 2012 - 10:24 PM

Another example showing the effects:

http://paulhaese.net...leflocking.html

#23 Jmel

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Posted 17 December 2012 - 04:52 PM

I saw this today while reading about flat frames:

http://alnitakastro....ernal-reflec...






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