Back to forums

0.95x coma corrector internal reflection problems?

TS-Optics Maxfield .95X Coma Corrector Coma Artifacts
19 replies•637 views
Oscar avatar
Oscar avatar
Hi all,

this coma corrector is also rebranded as Sharpstar 0.95x (or maybe Sharpstar was the original, idk), and probably a few more brand names

I was hoping that after I flocked my newt, I would have no internal reflections (there is not a spot that is not flocked, besides the spider itself; there is some light seeping in through the back of the scope, behind the primary mirror, but not enough to do anything)

but I got 2 rainbows, curvy, and crisscrossing in one small area of the frame; and I had this rainbow problem once before, before flocking the newt.

so I'm just asking, is it common to get rainbows in 0.95x CC images? does anyone else have them?

should I move to the Nexus? can the Antlia V-pro, and 3nm SHO filters handle F/3.7 without band-pass shift?

EDIT: it's worse than I thought; I see 4 rainbows all on one side of the image
andrea tasselli avatar
andrea tasselli avatar
I can't see nothing in mine, even when tested with APS-C sensor.. Moving to the nexus or any other CC would be the only realistic solution if you are sure it's an internal reflection otherwise it's wasted money.
Werner Stumpferl avatar
Werner Stumpferl avatar
I have the TS Maxfield 0.95 CC together with a APS-C on a 8" Newton, also flocked and I have no reflections or rainbows.
Maybe you have a problem with reflections in the OAZ-tube. Or if you use a filterdrawer maybe there. Also a tilter can make those reflections if there is a distance between tilter and camera.
Helpful Concise
Christian Großmann avatar
Christian Großmann avatar
I assume that you disassambled the primary mirror to get the material on the inner tube? I don't know if you have done anything on the screws that holds the mirror. It might be that they are too tight and there is stress on it. If you have fasten the screws, loosen them a bit.

I never had issues with any optical add-on I put into one of my scopes. That doesn't mean it would never happen, but I doubt it is the reducer itself. Rainbows should be caused either by a bad optical glass element or it is some kind of interference on a gap or similar. Don't know what other things might cause these issues.
Oskari Nikkinen avatar
Oskari Nikkinen avatar
Yes, this is a problem with the 0.95x coma corrector that comes in many names (mine was TS Maxfield labeled - but it is the same product).

I had exactly the thing you describe here on several different targets, a bright rainbow like arc somewhere in the image. An off-axis star at just the right distance outside your field of view will make this happen, presumably due to some sort of internal reflection issue inside the coma corrector.
Well Written Helpful Insightful Concise
Oscar avatar
Oscar avatar
Werner Stumpferl:
Also a tilter can make those reflections if there is a distance between tilter and camera.


I have tilt plate installed; it's the only way I can reach ~57mm backfocus

and it can't be that anyway, because I used the exact same camera/tilt plate/EFW/filters/OAG on my small astrograph without problems
Oscar avatar
Oscar avatar
Christian Großmann:
I assume that you disassambled the primary mirror to get the material on the inner tube? I don't know if you have done anything on the screws that holds the mirror. It might be that they are too tight and there is stress on it. If you have fasten the screws, loosen them a bit.

I never had issues with any optical add-on I put into one of my scopes. That doesn't mean it would never happen, but I doubt it is the reducer itself. Rainbows should be caused either by a bad optical glass element or it is some kind of interference on a gap or similar. Don't know what other things might cause these issues.

yeah, I had to remove the primary to flock everything; no, Celestron even glued the screws for the clips in place, so I didn't do anything to those

the bad optical glass element could be in the CC

Oskari says it's the CC
Oscar avatar
Oscar avatar
Oskari Nikkinen:
Yes, this is a problem with the 0.95x coma corrector that comes in many names (mine was TS Maxfield labeled - but it is the same product).

I had exactly the thing you describe here on several different targets, a bright rainbow like arc somewhere in the image. An off-axis star at just the right distance outside your field of view will make this happen, presumably due to some sort of internal reflection issue inside the coma corrector.

Thank you!!

just to confirm that it is the CC 100%

do you recognize this? (green is gone because of SCNR, but it used to be between the red and blue of the rainbow)

4 rainbow semi-circles
Oskari Nikkinen avatar
Oskari Nikkinen avatar
Oskari Nikkinen:
Yes, this is a problem with the 0.95x coma corrector that comes in many names (mine was TS Maxfield labeled - but it is the same product).

I had exactly the thing you describe here on several different targets, a bright rainbow like arc somewhere in the image. An off-axis star at just the right distance outside your field of view will make this happen, presumably due to some sort of internal reflection issue inside the coma corrector.

Thank you!!

just to confirm that it is the CC 100%

do you recognize this? (green is gone because of SCNR, but it used to be between the red and blue of the rainbow)

4 rainbow semi-circles

*Yes, very similar to what i saw with mine. I'll see if i can find an example and post here. Data is from 2021 if i recall so will do some digging.
Christian Großmann avatar
Christian Großmann avatar
Yes, these are the lenses, no doubt. But there is no really bright star in that region. But the nebula on the side of the rings is really bright itself. The star field might light it up really crazy.
Oskari Nikkinen avatar
Oskari Nikkinen avatar
@messierman3000 

Found 2 examples:





Please ignore the data itself, these were quick autostretches and screenshots. But it looks pretty much exactly as yours.

Kit at the time was an 8'' newtonian with the Maxfield corrector. To be completely fair here to all sides of the argument i cannot say with 100% certainty that the coma corrector was entirely at fault for these. But i can say that after moving on to another corrector (Paracorr) i have not seen them again. So i have a strong suspicion it was indeed some kind of internal reflection in the corrector itself.
Concise
Oscar avatar
Oscar avatar
yeah, it must be a problem with this CC

so now the question is, (because I'm focused on buying the Nexus), whether F/3.75 is too fast for Antlia LRGB (V-pro), SHO (3nm) filters
Oscar avatar
Oscar avatar
I was able to save the image with Clone Stamping and masked desaturation


Cygnus Wall in RGB - quick capture
Oscar avatar
Oscar avatar
I wanted also to show another problem I had

a different type of artifact that I couldn't see on the individual subs:


do you guys think it's the same problem?

it's a circular artifact again, but I only have this HA data, so I can't prove whether I'm getting a rainbow here too

my stacked flats have no circle, and my individual subs have no circle either

my darks and bias are good

14 x 60" and 1 x 300" lights were stacked together

I had a bug zapper running outside and it uses UV light, could it be from that? somehow did it bounce off the dew shield and somehow not get blocked by the HA filter? my scope was facing the general direction of the zapper.
Christian Großmann avatar
Christian Großmann avatar
I think so. Navy is a really bright star. Because this is a mochrome image, you only have one ring (should be red at the HA wavelength if it was a color image). The subs were too dim to see it. The stack reveals much more of whats in the subs.

It's crazy that even the star field of the cygnus area is able to produce those heavy reflections. It seems like every lens surface is adding to the problem. I never saw those things in any of my flatteners, coma correctors or reducers.
Christian Großmann avatar
Christian Großmann avatar
I took a look at the TS website. There are three sample images and the one that shows the corner and the center performance. In the sample image of NGC2264 there seems to be reflections around the bright star in the center as well. I wouldn't have noticed this but if you try to find it, you see it. I might be wrong, but even in the image that shows the performance, there seems to be an odd color change down in the right corner of the image. This looks very unnatural, although I might see more than there really is. It's hard to tell from the web images.

https://www.teleskop-express.de/de/astrofotografie-und-fotografie-15/bildfeld-korrektoren-fuer-teleskope-138/ts-optics-newton-koma-korrektor-0-95x-maxfield-3-element-2-anschluss-3822

So I assume, there are more people out there with those kind of problems. Not just both of you...
Helpful
Oscar avatar
Oscar avatar
here's further proof that the CC is a piece of junk

https://stargazerslounge.com/topic/408644-ts-optics-max-field-coma-corrector/
https://www.cloudynights.com/topic/891582-rainbow-coma-corector-issue/

I just got bad luck in choosing this specific CC
Michael Vogt avatar
Michael Vogt avatar
Hi,

I have exactly the same problem with my "Maxfield" CC.
I See this rainbow reflexions in my pictures.
It is much more visible when using my DuoNarrowband filter, but even with just the UV/IR cut filter I can see it.

After that I have switched to the original CC of my Sky-Watcher 150P Quattro and the rainbow shaped reflexions disappeared.
So I can confirm too, that the reflexions was causes by the Maxfield CC.

BR
Michael
Helpful Supportive
Oscar avatar
Oscar avatar
I got a TS-optics GPU 1x coma corrector, because the Nexus would make my scope too fast for my filters, and because the Paracorr was out of my budget

and I used all the money I could spend to buy the GPU

then I got a faint bad feeling that I would also get rainbows with the GPU, and that I should get a Paracorr instead; as usual, I ignored my gut and a couple days passed,, but then I saw this image a few minutes ago https://www.astrobin.com/kzp1x4/

do you see it? next to star HD5171. 

well, if that's a rainbow, I can only hope my copy of the GPU doesn't do the same thing; if it does, then this rainbow issue must be a common TS-optics thing, and TS-optics would need to refund me.

GPU is being shipped already, too late to cancel order
Oscar avatar
Oscar avatar
I'm relieved

I replaced the CC with the GPU, then flocked the back of my newt (on the outside, with only small holes for the collimation knobs to stick out), where I saw light creeping in behind the primary, then, I put a black sock (an old one) on my focuser, so light doesn't creep in through the slit going around the drawtube, then I flocked the secondary mirror holder, and a part of the edge of the secondary that's facing the focuser

FINALLY, no rainbows, no circles, everything is much better