so this is a telescope you built? On Sun, Sep 4, 2011 at 4:34 PM, Chuck Hards <chuck.hards@gmail.com> wrote:
Solar filters. Good topic.
Here is a picture of my 50mm f/9 table-top white light solar scope, with Baader filter installed over objective. The cell slides on and off. It fits snugly due to a felt liner.
This telescope is made of PVC and ABS tubing. The tube rings are made from sheet PVC, shaped with a router. The cradle plate is made from 1/4" aluminum, cut on a table saw. The eyepiece is a 26mm Plossl, the aluminum barrel components were turned on my mini-lathe. Yields about 17x with this setup.
http://i260.photobucket.com/albums/ii24/JethroTull1958/001-5.jpg
Here are some other detail shots of the filter cell and eyepiece:
http://i260.photobucket.com/albums/ii24/JethroTull1958/004-3.jpg http://i260.photobucket.com/albums/ii24/JethroTull1958/005-2.jpg http://i260.photobucket.com/albums/ii24/JethroTull1958/002-4.jpg http://i260.photobucket.com/albums/ii24/JethroTull1958/003-4.jpg
When I get some time I'll find the box with the solar cells I made for other small scopes, as well as some PVC cells for 25mm, 70mm and 80mm binoculars.
I also am about 90% done with a molded fiberglass cell for my 6" f/8 Newtonian, using the same mold that I made the dust covers from. I'll post pics of that soon, if anyone is interested. I just need to install the felt liner, and the Baader material itself.
Some notes on solar filters-
Make sure no stray light gets around your filter cell. It will degrade contrast, sometimes very adversely, depending on the light leak. This goes for both ends of the telescope, Newtonians especially.
Baader mylar is diffraction-limited. I like it a lot more than any of my commercially-produced evaporated metal-on-glass filters (Celestron and Thousand Oaks). The color is natural and not tinted strongly orange or blue. Contrast is much, much better and more detail is visible to my eye.
Mylar is more fragile than glass, but it's not as bad as you think. Pinholes can be filled with opaquing fluid, scratches darkened with a Sharpie. You need a lot of such repairs before the filter starts to degrade the image. It's also cheaper than glass, so you can have replacement filter material handy when needed. I have some Mylar filters that are approaching 20 years old, with no problems.
Glass filters can also be damaged. Unlike Mylar, they can shatter if dropped. The evaporated metal coatings on them are just as vulnerable as the coating on your telescope mirror. Even hardened dielectric coatings can be scratched and peeled. Frequent cleaning can damage them.
All solar filters, regardless of type, should be held up to the sun in front of the naked eye, for inspection before each use. Do not use if you see unfiltered sunlight coming through a pinhole or scratch. Repair or replace before use.
Forgive me if much of this is a repost. I have 54 unread list threads to wade through, lol.
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