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Baader ASTF 240 AstroSolar Telescope Solar Filter - 240 mm - ASTF-240
Baader AstroSolar White Light Solar Filters
The world's finest solar filter material, Baader AstroSolar Safety Film, is now available in a complete range of high-quality mounted Baader Solar Filters. Their innovative design and construction enables each filter to fit a wide range of instruments…from telescopes, to spotting scopes and camera Lenses, to binoculars. Each filter is precisely mounted at the factory onto special cells, guaranteeing a stress-free mounting that, unlike other mounted solar film filters, preserves the full optical quality of the Baader AstroSolar film.
Many ready-made filters stretch the filter material like a drumhead in order to make it look like a piece of glass. While it might look more pleasing to the untrained eye, the stretching process absolutely destroys the image quality, rendering the film useless for high magnification work. Baader AstroSolar is mounted entirely stress free in order to perform like a high precision plane-optical window; in other words, AstroSolar film must show slight ripples! When the film is put under stress by an improper cell mount its optical quality is degraded and it then performs just like a common glass filter made of untreated float glass.
With Baader Planetarium AstroSolar™, the color of the Sun is displayed as neutral white, which is its true color. Other films and most glass filters produce a blurry bluish, yellow-orange, or reddish 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 part of the spectrum.
Baader ASTF 240 mm AstroSolar Filter
with Temperature Compensated Cell
Fits 260-300 mm OD & 290-330 mm ID Telescopes
The Baader ASTF telescope solar filters are made in the most elaborate way to assure the best quality for both visual and photographic applications, including the highest magnifications and detailed observation of individual sunspots.
As mentioned above, AstroSolar film must not be put under stress, neither during mounting, nor when temperature changes occur. For this reason, all Baader ASTF Filters feature a temperature-compensated cell. The ND 5.0 AstroSolar film is cemented onto an injection molded ring that has the same thermal expansion as the AstroSolar Filter material itself. This free floating film carrier ring is held onto the aluminum frame with the help of another holding ring made of fiber reinforced plastic for maximum security against breakage of the cell. This temperature-compensated cell enables the AstroSolar filter material to retain its excellent optical quality at any temperature, be it -30°C or +50°C.
Each Baader ASTF comes with two sets (10 mm & 20 mm) of three injection molded centering bolts. These bolts have threaded brass inserts to center the filter cell in front of the OTA. Each bolt features an injection-molded rubber grip face that is designed to easily slide onto your telescope tube. However, once they are in place, they grip firmly to the tube and will not easily disengage. You will also receive three safety straps with adhesive pads, an instruction booklet, and some simple hardware to complete the installation.
Please Note: The centering bolts do not properly engage on the inner diameter of most SCT telescopes due to the limited depth from the lip of the OTA to the corrector plate. SCT users will be required to mount the filter on the outside edge of the OTA.
Baader ASTF 240 mm Solar Filter Specifications
- Best for Telescope Apertures: 230 mm -250 mm
- Filter Aperture: 240 mm or 9.45”
- Outer Cell Diameter: 330 mm
- Net Weight: 230 grams or 8.1 ounces
- ID Clamping Range with 10 mm Bolt: 290 mm - 320 mm
- ID Clamping Range with 20 mm Bolt: 300 mm - 330 mm
- OD Clamping Range with 10 mm Bolt: 270 mm - 300 mm
- OD Clamping Range with 20 mm Bolt: 260 mm - 290 mm
Check out the Baader Solar Filter Clamping Ranges for more information on filter installation, etc.
What About Your Finderscope?
Adding this solar filter to your telescope will adequately filter the light coming through your focuser, but have you considered what you’ll do about your finder scope?
Here are some suggestions for dealing with your finder that will assure you do not damage your eyes (or anyone else’s) by looking at the Sun through your telescope’s unfiltered finder:
- Remove Your Finder. Ditching your finderscope when solar viewing will remove the possibility of someone accidentally looking through it to spot the Sun. Of course, not having a finder makes centering the Sun in your eyepiece more difficult, but with practice, it can be done. Set the mount down so the telescope is pointing in the direction of the Sun. Put the main solar filter on so you can check your progress, and then move the telescope around until it casts a shadow that produces a nice, sharp silhouette of the scope. The OTA will look circular. Now move your telescope up or down with your hand controller, slow motion controls, or very carefully by hand if required while looking through the eyepiece. You will not get a warning when you are close, but you should be able to align with the Sun using this method. Practice ahead of time before any big event, like an eclipse, to make sure you’ve got the process down.
- Filter Your Optical Finder. This solution is not recommended for a reflex or red dot finder since it is too easy to accidentally look around the window. If you have one of these finders we recommend you either remove it or replace it with a dedicated solar finder (see below).
To make your optical finderscope safe for solar viewing you’ll need to buy a piece of Baader Solar Film for Visual Use. This film comes in different size sheets and cuts easily with scissors, allowing you to make your own filter. You can go super low-tech and use a rubber band to hold a piece of the film firmly around the finder or you can get fancy and build your own slip-on solar filter. However you attach the solar film, you need to make sure there are no light leaks at all and that it doesn’t accidentally fall off when you move your telescope around. Any unused film can store flat between two pieces of cardboard and will keep for years. It is nice to have around, just in case of a solar emergency :-)
- Buy a Dedicated Solar Finder. Check out the Tele Vue Sol-Searcher Solar Finder. This special finder can only be used when observing the Sun, but it works very well. The Sol-Searcher is reasonably priced and can be attached to your telescope with Velcro or with #10-32 screws (user supplied).