Help with RH200 halos/reflections - Forums

Hi,

I recently bought an RH200 MKII. The telescope looks like new and, after some minor tweaking (I still need to fine-tune the collimation), it delivers a very nice, flat field across my full-frame ASI2400. So far, so good.

However, I’m seeing some kind of halos or reflections around most stars. When shining a flashlight inside the scope, I can see some bright edges, although I’m not sure where they are coming from.

I’ve read online that this issue can be resolved by flocking the telescope, but I have no idea how easy or difficult it is to service an RH200.

If you have experience with the RH200, I’d really appreciate any advice or insights. Anything helps.

Cheers,
José

PS: The attached image is a crop of a 120s uncalibrated raw.📷 Screenshot 2025-12-18 103355.png

Those are not due to unwanted reflections but rather are the results of chromatic shift within the optics so I doubt it can be brought to a solution by flocking. In my experience the RH200 has been a terrible instrument I wouldn't touch with a barge pole. Good luck!

andrea tasselli · Dec 18, 2025, 05:24 PM
Those are not due to unwanted reflections but rather are the results of chromatic shift within the optics so I doubt it can be brought to a solution by flocking. In my experience the RH200 has been a terrible instrument I wouldn't touch with a barge pole. Good luck!

🫤OK, there are some reflections going but I never thought about chromatism. I will check with a mono camera and NB filers.

Thanks of the feedback

The chromatic shifts are only occurring for the out-of-focus part of the image, such as the halos. In focus is mostly the same focus as I remember it.

andrea tasselli · Dec 18, 2025, 05:38 PM
The chromatic shifts are only occurring for the out-of-focus part of the image, such as the halos. In focus is mostly the same focus as I remember it.

The attached image is in focus and close to the center of the sensor.

This could be chromatic effects along with a self-reinforcing diffraction effect:

https://app.astrobin.com/forum/topic/188005/reflectors/is-this-what-i-think-it-is#post-204347

If you still see the rings in narrowband, that’s it.

Tony Gondola · Dec 18, 2025, 05:44 PM
This could be chromatic effects along with a self-reinforcing diffraction effect:
https://app.astrobin.com/forum/topic/188005/reflectors/is-this-what-i-think-it-is#post-204347
If you still see the rings in narrowband, that’s it.

Thanks. According to the thread you pointed out, the patternt should not be visitble with L filter, but in my case it is clearly visible. I will definitely test with NB filters shortly.

Here an example on one of image of mine:

It is not very prominent because of the large pixels used but the red halo is bigger than the blue one.

I removed the camera and there are many shining circular surfaces inside the OTA. The corrector plate holder had two anodized surfaces that are very bright.

I then removed the primary and wow, I cannot believed the design of the baffle tube, it has 3 sections and it is short. You can easily see light comming from outside the secondary mirror. The concentric diffraction pattern matches the shape of the baffle tube.

I will 3D print a closed and slighty larger version of the baffled tube, if that don’t fix the issues I will flock as much as possible the rest of the tube. I hope I dont have to mess with the corrector plate.

📷 PXL_20251218_212704940.jpg📷 PXL_20251218_214430278.jpg📷 PXL_20251218_222605470.jpg

Honestly, this optical design is so far out of my experience zone I really don’t know where to start. I certainly wouldn’t start by changing things without first talking to someone who really understands the design, like the people who made it.

Tony Gondola · Dec 18, 2025, 10:53 PM
Honestly, this optical design is so far out of my experience zone I really don’t know where to start. I certainly wouldn’t start by changing things without first talking to someone who really understands the design, like the people who made it.

I completely agree, I already sent a couple of emails to OS. No response. I hope they reply with a solution, but in the meantime I will play with some ideas. AFAICT, as long as I don’t mess with the corrector, I’ll be OK.

I have designed a closed baffle tube to replace the stock one.

📷 Screenshot 2025-12-18 180646.png📷 Screenshot 2025-12-18 182934.png

Yesterday I did some tests without the baffle tube. I was expecting lots of reflections, but to my surprise there were none and the halos completely disappeared.

The scope still needs collimation, but I’ll wait until I 3D-print a new closed baffle tube.

I’m not sure why OS installed an open baffle—the RH200 actually works much better without it.

I’ll report back after installing the new baffle tube and fine-tuning the collimation.

Cheers,
José📷 Screenshot 2025-12-19 124233.png

UPDATE:

I carefully collimated the RH200, the collimation it self was very easy, however I had to replace two stripped screws, so I have to unmount the primary one more time. After replacing the screws collimation was fast and easy.

These are the results without the bafflle tube abd good collimation. Full frame color camera.

📷 Screenshot 2025-12-24 094245.png

IMHO this looks very good.

UPDATE:

I have further tweaked collimation, still no baffle tube and this is the result of 1 hour integration:

Small Center crop 4X zoom

📷 Screenshot 2025-12-25 123412.pngCorner and center of full frame camera ASI2400:

📷 RH200 Corners.jpg

So far, no weird reflections.

I am happy with the results and for now I will use the telescope without the baffle tube.

At first sight it looks good. 👍️