What does OD 5.1 mean for the ASSF AstroSolar® Filters?
Optical Density (OD) 5.1 means the filter reduces the intensity of sunlight by a factor of over 100,000, blocking harmful UV and IR radiation and dimming the visible light to a level that is completely safe for direct viewing through a telescope, spotting scope, or binoculars. It is the standard for white-light visual solar filters.
How do I securely attach an ASSF filter to my binoculars or spotting scope?
Every ASSF filter uses three adjustable centering bolts to create a firm grip on the outside of your instrument's tube. You slide the filter over the objective and tighten the bolts for a snug, centered fit. For maximum safety, you should also attach the included three safety straps, which prevent the filter from being accidentally knocked off.
Can I use an ASSF AstroSolar® filter for photography?
Yes, you can. While these filters are designated OD 5.1 for visual safety, they work well for solar photography. You will simply need to use slightly longer exposure times or higher ISO/gain settings compared to a photographic-only filter (like an OD 3.8), but they produce excellent images of sunspots and surface details.
What is the difference between the "ClearWhite" ASSF filters and other solar filters?
The "ClearWhite" designation refers to the neutral color balance of the view. Many other solar filters, especially inexpensive glass types, produce a strong orange or yellow-tinted image. The Baader AstroSolar® film provides a more natural white view, which many observers prefer for accurately judging the color and contrast of solar features like sunspots and faculae.
Can I use an ASSF filter to watch a solar eclipse?
An ASSF filter is ideal for observing the partial phases of a solar eclipse with your spotting scope, binoculars, or small telescope. It will allow you to safely watch the Moon's disk gradually cover the Sun. However, you must remove the filter during the brief period of totality to see the Sun's corona. Remember to replace it immediately as soon as the Sun begins to reappear.
Which ASSF size should I choose for my instrument?
Choose the size that matches the aperture class of your optic: the ASSF 50 is an excellent choice for converting a standard 8x50 finder or 50mm spotting scope into a safe solar instrument, while the larger sizes up to the ASSF 150 suit bigger spotting scopes, refractors, and other optical tubes. Because the adjustable bolts grip the outside of the tube, measure the outer diameter of your instrument's front cell or dew shield before ordering to ensure a secure fit.
