>
> -> the object is the same. The best pinholes are "poked" rather than
> -> drilled. Drilled holes are miniature tubes, where a carefully made
> it seems to me they should be as perfect as it can gets. After reading
> your comment on drilled holes being miniature tubes I now think
> holography pinholes are not a good idea, as the laser beam is so
> coherent that a drilled hole (tube like) won't cause any unwanted
> effect, chances are those pinholes are drilled. Have any comment on
> this?
I think you are right. Tubes don't work well for several reasons. For
one thing, they cannot offer as much angle of view. Also, there is much
more surface for light to reflect around in, and more edges which
contribute diffraction. Best holes are sharpened as much as possible.
Save your money. Your holes are better than the high priced ones.
> -> Oh yes. It helps to darken the silver to diminish flare inside the hole
> -> and from the surface of the silver. Selenium toner is what to use for
> -> that. DON'T use PAINT! Toner leaves the hole clean and does not change
> -> the dimension. Not so paint!
>
> I first spray painted them, now I don't darken them and get better
> results. Does selenium work on brass?
Selenium not so well. Try different toners. Maybe polysulfides? There
are ways of blackening brass but I cannot recall them offhand. Check out
literature on electroplating, also possibly sources of formulas for
patina. Selenium works great on copper. Brass is actually not
consistent, one sample to another. It is usually alloy of copper and
zinc. There are lots of different brasses so generalizations are not
possible.
Just be sure that what you use for blackening acts on the surface
molecules rather than covering them with another surface like paint!
Larry Bullis
Shoreline Community College