Re: [ATM] Advice on Solar scopes/observation

[Michael Lindner <mikell@optonline.net>]

On Sat June 17 2006 11:22 am, Nils Olof Carlin wrote:
> > I wonder, has anyone tried the Baader "diffraction limited" solar film
> > material sold by Astro Physics?
>
> As I recall, it was widely discussed on lists after its introduction a
> couple of years ago...

I've made a bunch of these filters, and they work great! It's also a great 
"club" project. You can buy the film in .5x1 meter sheets and make a lot of 
filters. The way I've been making them is as follows. Note that you need to 
build this robust enough to not come apart during observing....

Take a sheet of black-on-black foam board like this stuff 
http://www.allartsupplies.com/item.php?articleId=1338

Get a piece of sonotube at least 2" larger than the outside of the scope. Cut 
a ring about 4"-6" wide. Cut two circles from the foam board - one that is at 
least as big as the outside diameter of the ring, one that fits in it 
comfortably. Cut a circular opening of the baader film in both of the foam 
board pieces. Cut a piece of baader film at least 1" bigger than the hole. I 
attach the baader file to the foam board with lots of double stick tape, and 
add glue to the foam board - foam board areas.

Cut 4-8 slits about 1/2 way up the ring, and glue in some compressible foam 
(like seat cushion foam) at the bottom of the ring. The idea of the slits is 
to allow the sonotube to spread outward slightly when you push the filter on 
the scope. The result should be a snug fit on your scope that takes quite a 
bit of effort to pull off. I then glue the foam board sandwich to the ring 
opposite the compressible foam end. I use a carpenter's glue, and apply extra 
ro makea fillet when the first glue up is dry.

The result is a cheap light white light solar filter. Before each time you use 
it, hold it up without a scope and make sure there are no pinholes in the 
filter - if there are paint them over or apply a piece of duct tape to the 
filter. Make sure the filter is sturdy, and won't come apart, and is tight 
enough not to blow or be knocked off.

P.S. The "best" soalr observing I have done has been projection with my 6" f/7 
newt. I made a box out of black-on-black foam board with the top open and the 
bottom made of white foam board. It is very light. I rotate my scope in the 
cradle until the eyepiece faces the ground, then use rubber bands to attach 
the box and do solar projection. Up to 4 people can comfortably see what's 
going on, and I can project a 12-24" sun quite easily with a 27mm and 12mm 
eyepieces. The 6" aperture is enough to make an image bright enough to see 
details, but not so big that it will set fire to itself if the sun drifts out 
of the field. I aim it by watching the shadow of the scope on the ground...

-- 
Michael Lindner
http://www.starastronomy.org *** http://home.att.net/~mikel
http://www.atmsite.org *** http://www.atmlist.net
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