Celestron C6 question
Posted 15 November 2012 - 06:26 AM
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.
Posted 15 November 2012 - 07:39 AM
Posted 15 November 2012 - 09:56 AM
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
Posted 15 November 2012 - 03:11 PM
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.
Posted 15 November 2012 - 03:50 PM
Posted 16 November 2012 - 12:49 PM
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.
Posted 16 November 2012 - 02:20 PM
Posted 16 November 2012 - 03:18 PM
Posted 16 November 2012 - 03:40 PM
Posted 17 November 2012 - 10:30 AM
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.
Posted 17 November 2012 - 02:34 PM
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.
Posted 17 November 2012 - 07:04 PM
Posted 17 November 2012 - 08:28 PM
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?
Posted 18 November 2012 - 06:30 AM
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.
Posted 11 December 2012 - 02:44 PM
Posted 11 December 2012 - 10:02 PM
Posted 11 December 2012 - 11:45 PM
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?
Posted 12 December 2012 - 10:49 AM
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...
Posted 12 December 2012 - 03:39 PM
I now understand you are talking about the baffle tube, whereas I was referring to the secondary casing/baffle.
Posted 12 December 2012 - 08:41 PM
Posted 12 December 2012 - 08:57 PM
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.