Re: 3M flocking paint (again)

[P3D Brian Reynolds <reynolds@xxxxxxxxx>]

John R wrote:
> 
[MEGA SNIP :) ]
> 
> Perhaps you can use black velvet, or mix some rough material with black
> paint. Did you mention what you want to use it for?
> 

Black velvet (depending on the quality) is actually pretty bad for
this application.  Black velvet will reflect a lot of light at grazing
angles (which is what you're concerned with when trying to stop
internal reflections and lens flare) and its reflectivity depends on
which direction you have brushed it.  Velvet also sheds (depending on
quality) and you can wind up with contaminants on your optics and
slides.

Among amateur telescope makers there are several methods in use.

1) Paint all internal surfaces with flat black paint.  Krylon Ultra
   Flat Black is highly regarded.

2) Cover internal surfaced with flocking paper.  Edmund Scientific
   sells this, and it's pretty expensive (at least if you want to
   cover a 5 foot by 5 inch inner diameter tube).

3) Break up the surface smoothness of the internal surfaces.  How you
   do this depends on the materials you are using and how much work
   you want to put into it.  A first pass could be as simple as
   roughing up the interior surfaces with sand paper and then painting
   flat black.  For more effectiveness you can mix various things in
   with the paint to further break up the surface.  The idea is to
   apply a heavy coat of paint and then pour sawdust, crushed walnut
   shells, NoSlip (a material (crushed walnut shells) used in
   industrial applications to make horizontal surfaces non-slippery),
   or whatever you have handy onto the wet paint.  After the paint is
   dry you brush off the excess material that isn't stuck to the
   surface and then apply another coat or two of paint to seal the
   material in.  Repeat as desired.

-- 
Brian Reynolds                  | "Humans explore the Universe with five
reynolds@xxxxxxxxx              |   senses and call the adventure science."
http://www.panix.com/~reynolds/ | - Edwin P. Hubble


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