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Seymour Solar vs. Baader AstroSolar - Solar Filter Thin-Film Comparison
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In the interest of full disclosure I have no financial stake in any of the companies mentioned in this review. I live in the Phoenix, AZ metro area and have 15 years of experience in amateur astronomy. I use 2 scopes, a 6 inch late-model Orion Dobsonian and a 4 inch Galileo altazimuth Newtonian.
Believe it or not, there’s a little-known thin film solar filter on the market that is remarkably inexpensive and provides excellent performance. In the beginning, the only option was Mylar. Once Baader AstroSolar safety film hit the market, Mylar began to lose favor as the solar filter of choice. For close to a decade, Baader thin film has dominated the market in white-light solar filters and with good reason. Thin film filters are optically superior to metallized plate glass filters manufactured by companies such as Thousand Oaks and J.M.B. (which also manufactures the plate glass filters sold by Orion). The innate thinness of film filters, although they may billow when relaxed, means they are too thin to cause any significant distortion of the image. A plate glass filter, on the other hand, is typically not made of glass carefully figured to be truly optically flat. Thus, a ¼” layer of glass with subtle variations in the optical surface can impart distortions into the resulting image. Baader film performs so well because it is not only extremely thin, but can be used in a single layer due to the coatings being applied to both sides of the material (whereas older Mylar filters had light scatter resulting from internal reflection between the dual layers of filter material). This, combined with the fact that it gives a neutral white color image instead of the blue-tinged image imparted by older Mylar filters, has made the Baader film the dominant thin film on the market.
It was originally in going to my local telescope dealer with the intent of trying to purchase Baader film that a different filter material came to my attention. The dealer in question did not carry Baader film, but had a different thin-film material (that I had never heard of) from a smaller company called Seymour Solar (a name which when spoken aloud makes a terrible pun). The filter material is a stiffer, black material that vaguely resembles photographic film (as opposed to the billowy, silvery film produced by Baader). The material is sold in 8” by 11” sheets in a manila envelope protected on each side by sheets of gauzy lens cleaning paper. At 9 dollars per sheet, the material was an absolute bargain and would at least make do until I could order some Baader film from another dealer. The sheet was just large enough to make 2 filters; one for my 6” Dobsonian and one for my 4” Newtonian. I made filter cells out of foam-core board and electrical tape from a local craft store and made them to secure to the tubes of the telescopes by both snug fitting over the front of the tubes as well as further secured by Velcro straps.
Once I took the scopes out with the new Seymour filters attached I took my first looks. The image produced by the Seymour film is a yellow-orange color very similar to that produced by metal-coated glass filters. Indeed, I later had a chance to compare the view directly against a J.M.B. sourced Orion filter and the color was very nearly identical. The view is darker than that produced by Baader film. I consider this a plus as every time I’ve used a Baader filter I have found the view to be uncomfortably bright (but not dangerously so) without using additional eyepiece filters to dim the view. The sky background adjacent to the solar limb was deep black with the Seymour film, as it is with the Baader film.
The Seymour film provided excellent granulation and sunspot detail and ample detail of faculae (which popped out a bit better when augmented with an 80A light blue filter). Comparatively, the Baader film provided poorer granulation detail but better visibility of faculae (however, various eyepiece filters can be used to enhance granulation detail with the Baader film). Neither filter has the advantage in terms of detail within sunspots.
So which is ultimately the better filter material? Let’s look at the pros and cons of each:
Better visibility of faculae
Better versatility when combined with eyepiece color filters to accentuate details
Slightly higher cost
Uncomfortably bright view without additional eyepiece filtering
Less granulation visibility
Better visibility of granulation
Pleasing, expected orange color
Comfortable image brightness
Less versatility with eyepiece color filters
Less faculae visibility
I think I have to call this comparison a draw. The performance shortcomings of the Baader film in comparison to the Seymour can be made up for with the use of color filters to accentuate certain details, which isn’t an option with the Seymour film. On the other hand, the Seymour film is cheap, easy to use, and provides a superb view on its own without having to use additional eyepiece filtration (which is unfortunately a necessity with the Baader film due to the uncomfortably bright image). The end result is one of six of one, a half-dozen of the other. Both materials give excellent white light solar views at a low cost. The Seymour, while slightly less versatile over the long run, is a very good option for a solar filter on the cheap.