Black paint recomendation

[Zang]

Best is Musou Black, which absorbs 99.4% of light. Black 3.0 absorbs 97.5%. Vantablack is even better, but costs a fortune.

Thanks Toby! I paid $67 for my 28mm so for sure I do not plan to spend fortune on the paint or get it shipped from overseas. Beside, I have already applied permanent marker on the glass walls. The walls are basically ground glass surfaces so the maker ink looks ok there. It look decently dark and not shinny when looking at it from inside the objectives. However, one of the painted area which has a circle shape faces to the rear and the ink is visible when looking from the rear of the lens. It looks dark but a bit shinny and that is where I might be thinking about repainting if I can find something really flat, but relatively cheap and available. All I need is a tiny drop of the paint

[MEPER]

I used the Humbrol 033 after recommendation from Erik and it worked very well.
It came in small 14ml can. But you don't need much.

This paint was recommended by a German company selling equipment and Telescopes for looking at stars:
https://www.lack-albrecht.de/produkte/spezialprodukte/speziallacke/schultafellack/
It comes in big cans. I have a can but have not tried it.
It is a paint that is used for making a blackboard for drawing with blackboard chalk (if this is the correct name for it).
So, it is very matt I assume.
I remember the company suggested it to be diluted. Will probably require some experiments for best result.

[Zang]

Thanks Meper!

Humbrol is available online in Canada, but I could not find the exact product you purchased. On another hand, I tested my painted lens and I do not notice any issue with internal reflection so I might leave it alone until I need to paint another lens.

[MFloyd]

And there is Vantablack, the darkest black available, made of Vertical Aligned Nano Tubes.

https://youtu.be/QCI2KYhC8vk

But normally not available to individuals.

https://www.surreynanosystems.com/purchasing

[MEPER]

The Albrecht matte paint I got from this company (I might have been able to find it cheaper another place):

https://www.gerdneumann.net/english/instrument-building-parts-teile-fuer-den-fernrohrbau/totmatte-schwarze-optikfarbe-deep-black-optical-paint.html

About the dilution I mentioned earlier seems to be the suggestion to mix with fine sand to enhance the performance.
Now telescopes are bigger, so a larger amount of paint is necessary. Then the Albrecht may be a cost-effective alternative to other type of paint.

[Matthew Currie]

If you are not determined that the paint must be oil based, you could look for blackboard paint. I had a can of this once (oddly enough to paint a blackboard with) and it was very flat and non-reflective. 

[Zang]

Thank you MFloyd, Meper, Matt...

I think black board paint sound to be the most popular option. I see a bunch of them in Amazon. I might try one in my next project.

BTW, in the meantime I did the internal cleaning job for my Micro Nikkor 55mm f2.8 and its objective's wall paint was washed away as well. After investing the light path, In came to conclusion that the paint loss practically has no negative impact to the picture so I put the lens back without painting.