Agena Visual Baader Solar Filter for Finders and Binoculars - 70mm Cell ID (30mm On-Axis Filter Aperture)

A. Information About Our Ready-To-Use Solar Filters

Why mess around with trying to make your own filter cell when you can have a ready-made, high quality Baader solar filter at a great price? Agena's visual solar filters are available in several sizes to fit virtually any finder, binocular, or telescope OTA/dewshield between 40mm and 225mm in diameter. They are made from the famous white light Baader AstroSolar safety film made by Baader Planetarium in Germany. The filter aperture and axis design varies by size (see specifications below). The filter cells are made of tough ABS plastic (sizes up to 140mm) or cast aluminum (sizes larger than 140mm) and are fitted with nylon thumbscrews for a secure fit. Optional screws are available (see "Accessories" section on this page) to increase the range over which each filter cell can fit. We offer Baader AstroSolar filters in visual density, ND 5 (0.00001 transmission) for direct visual use only. This can also be used for photography.

B. Baader AstroSolar Safety Film - Brief Overview

In its September 2000 issue, Sky & Telescope magazine proclaimed Baader Planetarium's AstroSolarâ„¢ Safety Film to be "the new standard in solar filters." AstroSolar Safety Film delivers white light views of the Sun that are unmatched by any other objective solar filter or material. The views through AstroSolar display fine solar details, including fine penumbral detail, solar granulation, and lighter colored faculae. The disk is set against a dark background, free of the haze and scatter that is common in typical 'mylar' films or inexpensive glass filters. The performance of AstroSolar is even more remarkable when considering its very low cost. When combined with Baader's tips for a simple do-it-yourself filter mount (see below), anyone can construct a complete low cost, high quality, white light solar filter for any telescope.

What is even more important - with AstroSolar Film the Sun appears in its real color - neutral white (with only a slight bluish tinge). Other films and glass filters produce a blurry bluish or reddish/orange/yellow Solar image, thereby cutting part of the spectrum. Especially with an orange sun, it is very hard to see faculae regions which are visible predominantly in the blue wing of the spectrum.

Due to its neutral color balance, AstroSolar Film enables the use of various color (or interference) filters which allows the observer to concentrate on certain spectral passbands for investigations of different layers within the solar "atmosphere". It is also possible to further improve the stability and sharpness of the solar image through the use of the Baader Solar Continuum Filter (sold separately). Views of granulation and faculae are particularly enhanced through the use of this continuum filter, in combination with AstroSolar film. Users of achromatic refractors will be particularly pleased with the performance using this additional filter.

Please note that you cannot see solar prominences with white light solar filters such as this - that requires the use of sophisticated and significantly more expensive narrowband solar filters or telescopes.

C. Appearance of Baader AstroSolar Film and Solar Filter Cell

At first glance, Baader AstroSolar Film appear to be like ordinary aluminum foil. You will often notice streaks or bends on the Baader film you receive. Sometimes, it also appear that the film might be slightly "warped." This is perfectly normal and natural and does not imply that the filter film is defective or used. The optical and mechanical properties of the film are not compromised. Please also note that the "flashlight test" is not a good way of inspecting this film. Putting it right against a very bright light will show a very mottled and non-uniform appearance, but again, this is normal and does not indicate a problem with the film piece.

Also, the Baader film is mounted a bit loosely on the filter cell. Hence, it may appear slightly stretched or even loose and "billowy" and may flutter a bit in a strong breeze. Again, this is normal.

Our filter cells are hand-produced in small lots and may have a slightly rough finish or minor cosmetic blemishes in parts. They may also have casting imperfections that look very much like cracks, but are not. However, these are all cosmetic and have no impact on the performance of the filter.

D. Tips on Selecting a Solar Filter for your Telescope

- Do NOT buy a filter that is the same size as your telescope aperture. For example, a 90mm telescope requires a filter cell LARGER than 90mm.
- Measure the outside diameter of your telescope tube/dewshield. Pick a solar filter with a Cell ID ("B" = Inside Diameter in specifications below) that is slightly larger than this. Do not select a filter cell that is exactly the same size as your tube/dewshield diameter - it won't slide on.
- Make sure that the included screws are long enough to clamp down on your tube/dewshield. Longer screws are sold separately if you need them. See specification "C" below.
- Make sure that the filter you select is deep enough to securely sit over your tube/dewshield. Use the Inside Depth ("D") specification below to determine this. Some telescopes have a beveled/slanted dew shield - our filter cells are probably not deep enough for a secure fit on these telescopes.
- Our on-axis design filters are perfect for refractor telescopes, but are not suitable for most reflector telescopes (Newtonian/SCT/Mak/etc.). If you use these with reflector designs, a significant portion of the filter aperture will overlap with your secondary and will effectively be wasted. Use simple geometry to calculate what portion of the filter aperture will be blocked by your secondary and whether the remaining clear filter aperture is adequate for your needs.
- Our off-axis design filters may work with some reflector telescopes, but you should compare your telescope's primary/secondary schematic to our filter specifications. Your scope's secondary may overlap with the Baader film rendering a portion of it ineffective. Similarly, a portion of the film may lie outside the edge of your primary mirror. You can use the detailed diagram and specifications provided below to see what portion of the filter aperture can be used with your reflector or catadioptric telescope.

E. Product Reviews/Testimonials

"The solar filter mounted easily using the supplied thumb screws and, well, looked good on [my] scopes. I can say I felt "smart" for having bought the filter. Thanks for the quality product, good price, and excellent service."
- B. Pugh, Oakland, California

"The integrity of your filters put me at ease. I am very pleased with the views, and feel confident observing with your filter. The thumbscrews grip nice and tight to the front of my scope, and they don't chew up the finish. I know this filter will not just come off. These are a great value!"
- B. Chellis, Seymour, Connecticut

"No joke: last week, my dog took the filter off the shelf, ate the box, and ripped out the Baader solar film! Fortunately, the way your filter is set up, I was able to unscrew it and replace the film with [another piece]. I doubt you could do that with any other style of filter."
- S. Azmus, Kenosha, Wisconsin