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GSO RC8 internal reflections

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Hi all !

So I got an RC8", and am getting some reflections from nearby stars on most of my shoots.

I'm shooting with a baaderized 450D.

I've repainted the inside of the focuser and 2" extension tubes with black mat paint. I hope It's going to erase the problem but somehow I doubt it.

I use 2 main setups :

• RC + M90 tubes + TS2" flattener and 2" extension tubes + 450D

• RC + CCDT67 reducer and 2" extension tubes + 450D

The problem is being enhanced when shooting with the reducer.

On demand of TS, I have done a rotation test. That means doing the same shoot several times, but rotating the different elements by 90° individually for each shot. (camera, then focuser, the reducer-flattener, etc).

The reflection always showed up at the same spot.

Another possibility would be that stray light could enter directly into the RC, without going through the mirrors. Don't know if that's possible but it could explain some things.

I will do some tests with a big dew shield (+-40cm) and see if that solves the problem. The stars causing the reflections seem to be more or less 5° out of the field.

So If anyone has had the same problem, pleas feel free to advise.

I know it DOESNT come from the focuser. A friend of mine has an RC8 as well, but with a feathertouch focuser and he encounters the exact same problem.

picture without the reducer (with TS2" flattener) :


Picture with the CCDT67 :


The second one is of course untreated in any way. The first is a rough treatment after stacking. But the purpose is just to illustrate the problem.


Edited by philming
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Check the spider vanes for any reflections along with the outer ring of the scope (where the scope covers fits), the dew shield as you said will be a good test. also try without any flattener/reducer. what is your guiding? if you use an oag it may be reflections form the oag's prism. I image with a gso rc with a ts extension tube along with baader 2'' extension tubes and the only reflections i had were when i used a moonlite adaptor that was polished at the inside. The second case was when i was imaging ic434 and i had reflections from Alnitak. for the record i didn't have any reflections with the factory focuser nor with the new moonlite focuser i got recently

edit if you can borrow another camera try an imaging session in case it's the baader flter mod of your camera

Edited by kookoo_gr
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At the front of the tube, there are these little screw ends that are fixing the dovetail bars on the RC. I have already covered these with sticky cloth. I guide with a Lacerta Mgen and a 80/400 mounted side by side with the RC.

I don't think it's the camera either, since my friend obviously uses his own, and has the same problem...

I'm lost :-/

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It could be a similar problem to the insufficient primary baffling described in this post http://stargazerslounge.com/member-equipment-reviews/155750-gso-254mm-f-8-ritchey-cretien-first-impressions.html

The review deals with a 10" model but there could be a similar problem with the 8". The steeper light cone associated with the reduced configuration you use would certainly accentuate any baffling issues


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I've only just started imaging with a reflector (Yves' ODK14) and reflections are an issue both in taking the lights and the flats. At large apertures you have to find a way round it. If you only want about a metre of FL then all I can say is 'apo refractor.'

The ODK does not always get reflections but sometimes it does and the way forward is to move the scope around the image on a larger scale than 'dither.'

If really your RC cannot do what it is sold to do then you need to remind the vendor of the law regarding fitness for purpose. If it can be made to behave then they will doubtless be keen to explain. People do get results with those scopes but they need sorting, as do the cheap fast imaging Newts, and that is not for me so I avoid them.


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Yes, sorry I was thinking secondary but for some reason wrote primary :blob10:.

What you might try is to use some rolled up dark card to extend the secondary baffle - not as a solution but as a way of establishing whether insufficient baffling is the culprit responsible for the off axis reflections.

The problem if I read well describes a problem with the secondary baffle doesn't it ?

Is there any way to solve this or is my RC good for the bin ?

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  • 4 months later...

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