Seeking internal flat black coating recommendations for UltraCat 108 adapter

+1 on the Musou. I’ve used this on my filter masks to black them out, and others followed my lead with success.

One word of caution, is it’s a water based paint. While I haven’t had any issue with it in the year and a half of using, it could theoretically run if it gets wet again.

You can get Musou Black on Amazon and it is what I’ve used on all of my internal astro-parts for many years. Properly applied, it has a reflectivity of around 0.5% and it is likely to be the blackest paint that you’ve ever seen. The important thing is that to get that kind of performance, it must be applied with an air-brush; not simply brushed on. You don’t need a super high end air-brush. This is the one that I have and it works really well for this purpose: https://www.amazon.com/dp/B092D2YB8R?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2&th=1

Musou Black is water soluble and you’ll have to thin it a bit for the air brush. I’ve found that a 2:1 mixture of paint to water works well to prevent the air brush from clogging. You’ll have to apply about 6 coats to get full coverage but the effort will be worth it. The final result is extremely black and pretty durable. One note: Never touch the painted surface. That will “gloss” the paint and greatly reduce its anti-reflective properties. It will also rub off if you touch it. That’s because the air-brush process creates a “flock-like” surface that it pretty fragile. So…just don’t touch it and you’ll be fine. I’ve had parts in the field for well over ten years that have been painted with this paint and it holds up without any degradation. I’ve also never seen it chip or flake off in any way.

Do it right and this is the second blackest paint on the planet (by only a little bit)—and it’s affordable, easy to get, and easy to apply.

- John

@John Hayes what kind of surface prep do you prefer when painting with Musou Black? Especially for aluminum / anodized parts.

I used it a couple of years ago to blacken a dew shield. Applied several coats with a sponge and tapping motion. No degradation yet.

Here a comparison photo I did at the time:

📷 IMG_6F9FDF501A8C-1.jpeg

DavesView · Oct 30, 2025, 05:17 PM

I received the Musou and applied a little on a sheet of paper just to see. Man, this stuff is blacker than black. It is super dull when brushed on. I believe it would be just fine for suppressing any light reflection with a brush application, but taking John’s recommendation, I have also ordered up the suggested air brush. Having done that, I’ll wait and spray it on, having considerable experience in spraying everything from mastics, zinc coatings, enamels, other industrial coatings and epoxies. I tried rubbing it off the paper and it holds extremely well after just a couple of minutes. I’ll give it a test run on some anodized aluminum before I go with the intended part. As always, you guys are spot on with help. Thanks!

Dave,

It is indeed very black when brushed on, but wait until you see how much blacker it is when you air brush it. All the trouble needed to airbrush it may seem like overkill, but it really counts for some things like the inside of connector tubes. Just remember that we are trying to amplify the very faintest signals in an image so you don’t want even the smallest stray reflection to make it to the sensor where it can be easily revealed with an aggressive stretch. Good luck with it!

In case anyone has any doubts, here’s a photo comparing standard flat black spray paint to Musou Black (painted on) illuminated by a super bright light at the specular angle.

📷 Black Sandpaper.jpgHere is a comparison with a part from Precise Parts to a part I made and air brushed with Musou Black.

📷 ONAG - Gemini Adapter Black Comparison.jpgAnd finally, here’s another adapter that I made with Musou Black air brushed on the inside. It is so black that you can’t see any of the internal threaded AR structure without using an extremely bright light. Properly applied, this stuff is REALLY black!

📷 ONAG to FLI Adapter2.jpg

John

Glad you were able to rid yourself of the dreaded STX with a solid solution and successfully “flock” it!

Here is a photo of a custom part that I recently made for Adam Block’s telescope. The inside is painted with Mousu Black and the part is very brightly lit. Can you see the internal mounting lip on the inside (in the blackest region)? Yep, that’s how black this paint is!

John

📷 Photo of Pellicle Adapter 11-12-25.jpg