[ATM] How dark is dark?

[Michael Wheatley]

I understand that the best light trap is a long and narrow cone 
painted with gloss black.  Another version is a stack of razor blades 
that have been painted gloss black.  This would give you reflection 
of light going deeper into the cone or groove rather than scatter of 
light.  Light baffles of this sort would be complicated in a 
telescope but the only stray light would be diffraction from the edges.

The densitometry from gloss and matte photographic may be 
missleading.  The readings would depend on the angle of incident 
light and the optics of the densitometer.  It was said that the gloss 
black had a lower densitometer reading but I would expect gloss black 
to have much higher reflectance, especially at a low angle.

If the above is valid then whether you want gloss black, flat black 
or a mirror surface in a telescope tube would depend on the latout of 
the surfaces.  You would probably need a graphics ray tracing program 
like Povray to sort it all out.

Michael Wheatley