Sunday, November 8, 2015

Solar Filter Workshop

The advantages of an astronomy club are many - of course there are the social aspects of spending time with people who share your interests and passions. But occasionally there are more utilitarian roles when volunteers with experience step up and show others techniques or how to do things. A case in point is yesterday's solar filter workshop. Former TAAA (Tucson Amateur Astronomy Association) president Bob Gilroy, assisted by Dennis, ran a half-day workshop on making solar filters for your telescope (22 attendees!). Now there are many types and kinds of telescopes, but Bob sticks to a standard design that can be adapted from a big Dobsonian to a pair of binoculars. Indeed, all kinds were produced yesterday! And fortunately, with group buying power, total workshop expense was only $12, a small percentage of what a commercial filter would cost.

So starting at the ungodly hour of 8am (on a Saturday!), we gathered at the USGS building on campus. Bob explained in general terms what the design was and how to implement it. He had emailed us the set of instructions earlier. Most had printed them out - unfortunately, I hadn't thought that far ahead, but his description made sense and I was able to wing it as I watched others.

Folks jumped right in with rulers, straight edges and sharp implements (razor blades and compasses!). In general terms, you measure the circumference of your telescope and cut a foam-core board long enough to wrap it. Crease one side with a ruler edge to dimple it so it can be bent around the telescope. Then cut a pair of pieces to sandwich the Mylar filter material between them, all attached with good-ole Elmer's or wood glue. Before handing out the fragile and expensive filter material, Bob inspected our handiwork. Rough edges could damage the filter with time, and gaps in construction where sunlight could leak in were not allowed.

The morning flew by. While supplies were furnished, folks were asked to bring in tools and supplies as well to minimize wait times. I had a ruler and glue which got passed around, and I made numerous use of neighbor's straight edge, tape and sandpaper. While the workshop was scheduled for 4 hours, I think only one fellow finished in that time. Bob had the additional foresight that since the filter is pretty fragile, we would also make a storage box for it, so that added to the time. By that time, though, we were old hands at foam board construction, and with the straight edges, boxes were easy! Still, time flew by, and I finally finished about 1pm.

Of course, the final test is to examine the sun through your completed filter. We needed to bring in our scopes to get the most perfect fit, though I didn't have a mount for it. At left, Dennis inspects the filter than Alan at right had made for his binoculars (a non-standard design). At right, my modest efforts are documented. I chose to made a visual filter for the TEC 140, so the filter has a clear aperture of 140mm. I also chose the "Baader" solar filter material. While there was also a "Seymour" filter material that gave a very pleasing yellowish disk of the sun, the Baader film gave a slightly brighter image, and since I do a lot of sunset images, I figured more light with the sun so low would be very useful.

So I waited until I got home to try out my handiwork on the scope. Good thing that I didn't wait too long - when I went to open my box, I found that the glue had leaked enough that it was glued shut! Fortunately, with only a little foam core damage on the box, I was able to extract the filter and try the fit and performance on the TEC 140. It fit perfectly and the brightness was great as well. At right is a 2000th second exposure of the sun after setting up. North is up in this image - a few small sunspot groups can be seen, as well as limb-darkening (edge is slightly darker) from looking through more of the Sun's atmosphere at its edge. For a non-tracked image, resolution and sharpness is great. And even though I would have preferred a more yellowish cast, I can always add that in Photoshop if I need to!

Anyway, it was a great morning, many thanks to Bob and Dennis.  It was fun to spend time with members and get to know them a little better.  Seems like back in "olden" days, we had a lot more social activities both under dark skies and also at meetings and other activities which seem lacking today.  But it was nice to get a "twofer" with both the social activity and get something to show for it!

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