Supermatt black paint for inside optical tube?

[RobH2020]

I've heard of people flocking the inside of their optical tubes, with various substances. 

I've just come into ownership of a tube of "black 3.0", the "mattest, flattest black paint" commercially available, and only just more reflective than the substances made by the vantablack producers used on scientific-level equipment. 

I was wondering about painting the inside of my OTA with this, probably just around the top end around the secondary mirror. 

Any thoughts?

https://culturehustle.com/products/black-3-0-the-worlds-blackest-black-acrylic-paint-150ml

[Astro-Geek]

I used some of its predecessor, "black 2.0" to paint the inside of a 250mm GSO newtonian and it was indeed much better than any matt black paint I'd tried before.

Most so called matt black paints may appear to be non-reflective when viewed face-on, but at an angle they usually become surprisingly reflective.

Hence people resorting to flocking or baffles.

The black 2.0 was very good though, almost as good as flock, and much easier to apply. 

I also covered the spider vane, back and edge of the secondary, the part of the focus tube that protruded into the OTA, and all of the fixing nuts inside.

 

Edited May 8, 2020 by Astro-Geek

[RobH2020]

2 hours ago, Astro-Geek said:

I used some of its predecessor, "black 2.0" to paint the inside of a 250mm GSO newtonian and it was indeed much better than any matt black paint I'd tried before.

Most so called matt black paints may appear to be non-reflective when viewed face-on, but at an angle they usually become surprisingly reflective.

Hence people resorting to flocking or baffles.

The black 2.0 was very good though, almost as good as flock, and much easier to apply. 

I also covered the spider vane, back and edge of the secondary, the part of the focus tube that protruded into the OTA, and all of the fixing nuts inside.

 

Ah nice, thanks for sharing your experience! Did you find it made much difference to your viewing experience? Black 2 absorbs 96% of light, black 3 99%, and vantablack 99.9% 😉

[Astro-Geek]

I'm fortunate enough to observe from an area with quite low light pollution (Bortle 4), and the nearest street light is about 5 miles away 🙂, so it's difficult to compare the before and after for general viewing given other variations in conditions.

Probably the best indicator I have is during bright moon periods there's far less reflection down the tube when I'm trying to view deep space objects close to its glow.

Also, when applying the paint in the daytime, the difference when looking along the tube after it has dried is markedly less reflective than the manufacturer's standard matt black paint.

[johninderby]

I’ve found flocking is most effective at reducing the effect of light coming from the side.as is often the problem in built up areas. Not as needed out in the countryside though.. 

[david_taurus83]

Word of caution if using that Black 2.0-3.0 etc, it's good but prone to flaking off if scratched. Might be ok on a non contact surface like the inside of a tube etc. I used it on a focuser and found it came off too easily when inserting or removing a nosepiece. Had to clean the mirror eventually!

[Astro-Geek]

4 hours ago, david_taurus83 said:

Word of caution if using that Black 2.0-3.0 etc, it's good but prone to flaking off if scratched. Might be ok on a non contact surface like the inside of a tube etc. I used it on a focuser and found it came off too easily when inserting or removing a nosepiece. Had to clean the mirror eventually!

Yes, an important point.

When I paint my Newtonian focus tubes, I mask any area that will have friction afterwards, so I don't paint the inside for the depth of any inserted eyepiece, and I only paint the outside at the bottom, the part that extends into the OTA, and I'm careful to not get any where the roller bearings press against it.

[Astro-Geek]

5 hours ago, johninderby said:

I’ve found flocking is most effective at reducing the effect of light coming from the side.as is often the problem in built up areas. Not as needed out in the countryside though.. 

Yes, no argument there, the random facets of the individual surface particles of the flocking absorb any light from deflecting down to the mirror. Unlike the smooth surface of the metal tube.

[Davey-T]

Just bought this for mine.

Dave

[johninderby]

Used the Krylon on the vanes etc on my Bresser dob. Coupled with flocking it is rather black in there. 👍🏻

[markse68]

Does flocking tend to hold moisture? 

[johninderby]

Not as far as I know. Not being as cold as the metal doesn’t seem to attract moisture. 

[Neil H]

Hi I flocked my 150/750 when I had it and also done my OO VX8L , got the sheets from FLO it's really sticky just remember to score it So it can expand with telescope

[Louis D]

2 hours ago, johninderby said:

Used the Krylon on the vanes etc on my Bresser dob. Coupled with flocking it is rather black in there. 👍🏻

The real acid test is to remove the mirror an put the tube at a shallow angle to the sun and see how bright the tube wall looks.  I've yet to find a flat black paint that doesn't look shiny at shallow angles under these conditions.  Perhaps if there was one that sprayed actual 3D particles forming tiny light traps it might work better.  I'm thinking along the lines of the fake hair sprays of the 80s/90s.

[discardedastro]

13 hours ago, Louis D said:

The real acid test is to remove the mirror an put the tube at a shallow angle to the sun and see how bright the tube wall looks.  I've yet to find a flat black paint that doesn't look shiny at shallow angles under these conditions.  Perhaps if there was one that sprayed actual 3D particles forming tiny light traps it might work better.  I'm thinking along the lines of the fake hair sprays of the 80s/90s.

That kinda is what the Black 2.0/3.0/Vantablacks of this world do.

Flocking is still always going to be more effective because of the surface area the material provides for absorbtion.

[markse68]

14 hours ago, Louis D said:

The real acid test is to remove the mirror an put the tube at a shallow angle to the sun and see how bright the tube wall looks.  I've yet to find a flat black paint that doesn't look shiny at shallow angles under these conditions.  Perhaps if there was one that sprayed actual 3D particles forming tiny light traps it might work better.  I'm thinking along the lines of the fake hair sprays of the 80s/90s.

Gerd Neumann recommends just blackboard paint and suggests mixing it with sand for that very purpose- but obvs brush on. I guess you could do that with the black 3.0 too for ultimate solution? 

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

This stuff is meant to be good too- Rosco supply film and broadcast with super saturated paints- for green screen studios etc. More economical than black 3.0 too. Might have to experiment...

https://shop.flints.co.uk/Products/ALL/ROS16003

[Astro-Geek]

An interesting idea, adding something to the paint that would dry as a non-smooth surface.

It's an established DIY method with boat decking.  International paints sell a very fine sand to be sprinkled on wet varnish to provide a non-slip finish for decking and dinghy floorboards.  I've used it with great success for that purpose (but not 'scope flocking).

That gives a very even surface finish, becuase after it is sprinkled on when the paint has partially dried but still tacky, the excess can be shaken off.

Might be a problem with using it as a "liquid flocking" though, because the top surface would need to be painted again with the matt black.

My biggest reservation though, would be that any particles of sand that later become dislodged might drop on the primary mirror... 😱

 

[ollypenrice]

The issue of mat black paint came up some years ago. It transpired that paints using dyes tended to be reflective in some wavelengths. I think it might have been IR from memory. To avoid this it was recommended that we use pigment based paints such as are used in high temperature applications like stoves. I don't know the paint under discussion here.

Olly

[RobH2020]

On 10/05/2020 at 14:34, ollypenrice said:

The issue of mat black paint came up some years ago. It transpired that paints using dyes tended to be reflective in some wavelengths. I think it might have been IR from memory. To avoid this it was recommended that we use pigment based paints such as are used in high temperature applications like stoves. I don't know the paint under discussion here.

Olly

What's the issue of black paint possibly reflecting infra-red? There's not enough energy in the EM radiation at night to do any eye-damage I would guess... and we can't see IR so doesn't affect viewing?

[RobH2020]

On 08/05/2020 at 20:55, Louis D said:

The real acid test is to remove the mirror an put the tube at a shallow angle to the sun and see how bright the tube wall looks.  I've yet to find a flat black paint that doesn't look shiny at shallow angles under these conditions.  Perhaps if there was one that sprayed actual 3D particles forming tiny light traps it might work better.  I'm thinking along the lines of the fake hair sprays of the 80s/90s.

I guess it depends what you mean by shiny. Black 3.0 definitely doesn't look "shiny" in the typical sense of the world. It does reflect some light - e.g. I've painted a golf ball with it, and when you're up close you can tell it's a 3D object with dimples. From 2-3m away (social distancing) it looks like a perfectly black hole in the fabric of spacetime.

[ollypenrice]

1 hour ago, RobH2020 said:

What's the issue of black paint possibly reflecting infra-red? There's not enough energy in the EM radiation at night to do any eye-damage I would guess... and we can't see IR so doesn't affect viewing?

It can affect imagers, particularly when taking flats.

Olly

[RobH2020]

2 minutes ago, ollypenrice said:

It can affect imagers, particularly when taking flats.

Olly

Ah thanks - forgot about imagers, knowing nothing about the subject  

[ollypenrice]

2 minutes ago, RobH2020 said:

Ah thanks - forgot about imagers, knowing nothing about the subject  

I wasn't sure what your intended use was. I'm sure it won't matter for visual.

Olly

[PeterW]

Blackening some new eyepiece tubes and had some spare.... looks like yoda has joined the dark side 😉 (under bright light with camera exposure stretched.. it’s not brown!)

 

Peter