Re: [APML]: Telephoto

[Chuck Vaughn <aa6g@aa6g.org>]

Hi Mike,
> 
>         I'm also wondering how an Orion Skyglow filter will affect exposure
> times for nebulae on B&W film (Tmax 400 or TriX 400)

After looking in the Orion catalog I see that the Skyglow filter has a 
similar curve to the Lumicon Deep Sky filter. It's generally quoted that 
you can increase the exposure by 3 times with the DS filter as compared
to
white light. The same should hold for the Skyglow.

> and if it will help at
> all for galaxy and cluster shots. I get the impression that the Wratten #25
> red filter works best for these (galaxies and clusters) on B&W.

White light works best for clusters and galaxies. If you use a red
filter
on a galaxy you'd just have to go 6 to 10 times as long to record the
same amount and you might suppress the arms, which tend to be bluer. One
of
these days I'm going to try my blue short pass interference filter on
M31 to
see if it is possible to enhance the arms. You might like to take a peek
at my
article on filters on my web page. It explains all of this better than I
can
here.

http://www.aa6g.org/Astronomy/articles.html

> I've seen
> these filters that fit 1 1/4" eyepieces, but how do I get one in the light
> path at prime focus of my scope?

Orion sells a 2" version that fits on 2" adapters and OAG's and a SCT
version
that fits on the rear cell of 8" SCTs.

Chuck Vaughn  <aa6g@aa6g.org>