DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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Hello all,
I own an Orion Apex 90 which I bought for ultimate portability and also solar observing and I am very happy with both of these aspects.
Also, the scope is great in both planets and the moon, EXCEPT:
I see eliptical reflections when a bright object (planet or star) is close to the edge of the field of view, or even when it is closely outside. They look like coma (according to Rutten & Van Venrooij the Gregory-MCT design does have coma in this direction), but hey, I if that is coma, then my 10XTi should show the same things in the opposite direction!!
I sent the scope to Orion and they didn't find anything, but sent me another OTA in sign of good faith.
After that I:
- Installed dew shield: Same thing.
- Covered the outer 0.5" of the corrector to see if it is coming from reflections in this area: Same thing.
- Covered with blackened paper the inside metallic ring which is behind the corrector: Same thing.
- Covered the whole inside of the OTA with sandpaper painted mate black (due to lack of baffling): Same thing
BTW, the sandpaper does reduce reflections A LOT. I shined a green laser on it and looked the reflection on the wall - HUGE difference compared to the OTA's original inside.
I have read the review in CN which mentions the same thing, as well as one of the reviews in www.excelsis.com where this is mentioned, so I knew where I was getting into. Plus, I would not mind fiddling with this inexpensive scope.
So:
- Any idea what the root cause is? I tried all fixes I could think of. Looks to me that it is probably an inherent problem with the optical design.
- Do the Orion MCT owners of the 102 and 127 see such reflections or is it only on the 90 model?
Many thanks folks,
Dimitri
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Rat8bug
Pooh-Bah
Reged: 01/07/05
Posts: 1289
Loc: Michigan
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Well, I have experienced no such symptoms with my 127mm mak:
http://www.barrie-tao.com/apex127.html
I find using using sandpaper a bit crude, as those abrasives would cause serious damage to the optics if they should flake off. Flock paper would have been a better idea IMO.
A compound telescope reaches optimal correction at a single focal length. When the narrow range of mirror to secondary distance is exceeded, then the performance is degraded. I would install a Helical focuser to obtain diffraction limited performance this scope should be capable of. Here is a link on the procedure....
http://www.easter-vivian.e7even.com/jim/astro/mak/index.html
Ciao...Barry
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Nikon D40/D50/D70 DSLR
WO 105mm Triplet APO
WO Zenithstar 66SD APO (Black 'n Blue)
WO 8 x 45mm APO Bino
UO 20 x 80mm Bino
Vixen 80SS Refractor
Orion 127mm Apex Maksutov
Vixen GP-DX with Skysensor 2000
SBIG STV and e-finder
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DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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Thank you Barry.
So, the 127 does not show the problem.
Anyone else? Only one reply? 
Thanks again,
Dimitri
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chazcheese
professor emeritus
Reged: 11/21/04
Posts: 545
Loc: Phoenix, Az
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I haven't seen this in my 102, but I haven't really looked either. Supposed to go out tonight so I'll take a look.
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chuck
10" Orion xt
8" Meade LX200 mount/2080 OTA
C4R on CG5
Vixen ED80Sf on Porta Mount
AT-1010
PST
12X63 mini giants
15x70 Skymasters
Virgo Bino mount on Sanford/Davis tripod
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DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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Chuck,
That would be great! Thank you very much. I hope the sky is clear 
Easiest way: Pick Jupiter, center it, and then start to move the planet accross your FOV until it's completely out. If you have the problem, you will figure it out immediately.
Cheers,
Dimitri
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chazcheese
professor emeritus
Reged: 11/21/04
Posts: 545
Loc: Phoenix, Az
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I tried with three different eyepieces ( 10 & 25mm plossels and a 13mm kelner ) and didn't see anything like you descibed. The view was as sharp at the edge as at the center, also had another person verify ( 40+ years experiance ) and he didn't see any problems. He was actually impressed with the view. The only problem I saw was a reflection off the side of the inner wall on the kellner eypiece when Jupiter was just off or at the very edge of view. Hope this helps.
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chuck
10" Orion xt
8" Meade LX200 mount/2080 OTA
C4R on CG5
Vixen ED80Sf on Porta Mount
AT-1010
PST
12X63 mini giants
15x70 Skymasters
Virgo Bino mount on Sanford/Davis tripod
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stevie
Spiderman
Reged: 12/07/03
Posts: 3132
Loc: Belgium
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you might wanna examine the exit pupil in daytime
just point your scope to something bright (a white wall or a cloud or just the sky)then insert a eyepiece with low power(bigger exit pupil)
now take good look at that exit pupil from a distance
you should see a white disk with a black spot surrounded by black
here's a picture of my mak
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stephane
Our shots(updated :18.02.2008)
My videos
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DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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Thank you all! Chuck, if the reflection you mentioned is only with the Kellner, I assume the eyepieces are ruled out (in any case, I have a UO HD, a GSO, Orion and Celestron plossls - they all show it). Thank you for the test!
So, to summarize, no such issues with either the 102 or the 127 ... good for you guys - bad for me. Too bad any fix I tried does not address the problem.
Stephane, I am listening. I haven't done the test yet, but I assume the picture you show is a good example. What is a bad example and what does it mean?
Thanks again,
Dimitri
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DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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OK, I couldn't wait and I did the test. Actually, the bright white disk is surrounded by a much much brighter "halo"! And as I looked more carefully, this halo comes from the inside of the narrow long tube which goes through the primary mirror! And as I looked sidewise, this reflection was becoming much more prominent!
Stephane, your test may have discovered the true source of the reflection!  I'll try to flock the inside of this tube.
I'll do more scope surgery and then return with more news 
Gotta go all, I have a scope to tear apart 
Dimitri
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stevie
Spiderman
Reged: 12/07/03
Posts: 3132
Loc: Belgium
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yup i had the same problem with the scope
i just rolled up a piece of sandpaper(black of course) and shoved it up the baffletube
problem solved and i have no problem with debri falling off the sandpaper
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stephane
Our shots(updated :18.02.2008)
My videos
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southmike
Carpal Tunnel
Reged: 11/22/04
Posts: 2817
Loc: Fayetteville, NC
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hmm just stumble on to this post..
I have a 90 mak with this., and i know one other , poster has this problem..
when you are slightly off a bright star or planet, you get a chromed looking arc or oval ring?
I will investigate further..now.
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group scope pic
my refractors
LX200 10"-St120
LX200 8" f6.3-Orion 80ed
LX200 8" f10-Orion 90 Mak setup pic
Meade 102ED LXD650
Sky Watcher 100 ED Triplet prototype
Nexstar 5
etx125
etx70's
Edited by southmike (05/02/05 05:38 AM)
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Starman1
Postmaster
Reged: 06/24/03
Posts: 10675
Loc: Los Angeles
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Stephane,
The light area in your photograph, and the black image of the secondary, are both elliptical. Yet the reflection (faint) from the baffle and visual back are round.
this implies that both the primary and secondary mirrors are tilted (one perhaps to compensate for the other).
Does your scope exhibit astigmatism when focusing (star goes from oval just outside of focus to oval in a 90 degree direction just inside focus)? If so, your scope is out of collimation and needs adjusting.
This site can help: here.
And the top file on this site is directly applicable:
here.
These will help a lot.
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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And ...
It is a fact. The reflections inside this tube are the cause!!! I have tried a couple options, and with each one I could modulate the reflections I was seeing. Jupiter always the best test.
Many thanks to Stephane for his test  . The sandpaper solution did not work for me so well, because I have too thick sandpaper (the reflections were gone, but the tube was not round). My efforts to paint the tube improved but not eliminated the problem. I will try flock paper next.
But the essence is that the cause of the problem is found and the solution is under way!  I will sleep a happier man tonight!  
Cheers,
Dimitri
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stevie
Spiderman
Reged: 12/07/03
Posts: 3132
Loc: Belgium
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hey Don
thanks for the concern but it's just a no so great picture
what you see in that picture is movement
here's a better version ,i had to look all over my place for close up rings extension tube ect.. to create enough distance between the camera and the eyepiece but it worked out
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stephane
Our shots(updated :18.02.2008)
My videos
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stevie
Spiderman
Reged: 12/07/03
Posts: 3132
Loc: Belgium
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here's a closer look
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stephane
Our shots(updated :18.02.2008)
My videos
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southmike
Carpal Tunnel
Reged: 11/22/04
Posts: 2817
Loc: Fayetteville, NC
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interesting the halos are in that picture towards the top of the tube..makes me wonder..if that is the culprit...stray grease maybe?
i wonder if flat black like chalk board paint would do the same thing...i would think that would not reflect anything well
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group scope pic
my refractors
LX200 10"-St120
LX200 8" f6.3-Orion 80ed
LX200 8" f10-Orion 90 Mak setup pic
Meade 102ED LXD650
Sky Watcher 100 ED Triplet prototype
Nexstar 5
etx125
etx70's
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Starman1
Postmaster
Reged: 06/24/03
Posts: 10675
Loc: Los Angeles
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At low angles of incidence, flat black paint is nearly reflective. I flocked an 8" SCT a while back and the difference in scattered light was profound. That SCT had a series of baffles in the primary baffle, though, unlike most of these inexpensive MCTs.
There is a test of flocking materials' reflectivity here on Cloudy Nights, but I don't know the link at the moment.
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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I tried flat black paint, not so good. I am ordering flock paper.
Dimitri
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Darren B
super member
Reged: 05/02/05
Posts: 163
Loc: Poole, Dorset UK
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I have a Starmax 90 with similar problems and thinking of flocking the baffle tube. Can you insert the paper through the rear of the scope or do you have to take of the front corrector lens as well? Apologies if this is a simple question as I have no experience taking a mak apart and my scope is perfectly collimated and does taking off and putting back on the front lens affect collimtion or not? 
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Darren
WO ZS80FD 10th AV with Vixen Porta Mount
Skywatcher Equinox 66ED
William Optics 7x50
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DIO
super member
Reged: 11/12/04
Posts: 101
Loc: KY, USA
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Darren,
After taking the scope apart and putting it back together for, oh ... say 25 times  , I can tell you that for this particular solution you do NOT need to take it apart. You can just insert the paper from the rear. I have tried it with regularly painted black paper (the flock paper has not arrived yet) and I had no problems taking it in and out.
As for the collimation, I could not tell if it changed when I removed the front corrector - if it did, I could not detect it. But then again, I did not do a thorough check.
Cheers,
Dimitri
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