RE: ATM more binoviewer nonsense

[Andy Saulietis <iss@pvtnetworks.net>]

Tom K writes,

>The only disadvantage I've found with the cube beamsplitter I use is that it
>also polarizes the light...one path is vertical, the other is horizontal.
>That has not been a problem with night observing, but if I observe the
>planets during daytime...the blue sky background can be very different
>between the two eyes.  (Speaking with Al Nagler at TSP 2000 - he mentioned
>his bino-viewers also have this polarized light, but he didn't seem overly
>concerned...not many people seem to use them for daylight planet observing,
>so it's not a major detriment.)


Some of the older (surplus) beamsplitters were actually
30%/30% transmission,40% absorption, not good for looking
at faint stuff. The newer dichroic type beamsplitters
have far less absorption losses, but also more $...

Another type of beamsplitter is the pellicle, which is
a *thin* nitrocellulose film on an optically flat open
frame. The same stuff used to clean optics. It transmits
92% & reflects 8% as is but can be evaporation coated
to be 50/50 T/R. Pellicles are made by putting a drop
of the nitrocellulose/ether on water, when dry its
lifted off the water with the frame. Never tried this
so don't know the details of how to lift/tighten the film
or how one would coat the film. Pellicles are *fragile*
and impossible to clean & are ususally used in a sealed
volume.

The 8% film might be usable as a pickoff for guiding, allowing
guide stars to be selected in the imaging field. I was experimenting
with this technique at NASA a few years ago, never finished it
before I retired..:)



Andy Saulietis
ISS Enterprises
39 Silver Fox Trail
Mayhill NM 88339
505-687-3067 voice
505-687-3021 fax, call voice or e-mail to set up
e-mail: iss@pvtnetworks.net