How to Choose the Right Astrozap Solar Filter

The sun is a fascinating, dynamic object. Its surface is surprisingly detailed and changes frequently. The observing hours are more convenient. However, there are a few rules to follow before using your telescope on the sun. The first rule of solar observing is never point your telescope at the sun without a proper filter. The second rule of solar observing is always inspect the filter before placing it on your telescope prior to observing to ensure that there are no defects (scratches or pinholes) that could damage your eyes or equipment. IF YOU DISCOVER ANY DEFECTS, DO NOT USE THE FILTER—IRREVOCABLE EYE DAMAGE COULD RESULT FROM THE USE OF A DAMAGED SOLAR FILTER ALSO, NEVER MOUNT A SOLAR FILTER ON ANYTHING OTHER THAN DIRECTLY TO THE OPTICAL TUBE.

If you have a finderscope or similar device on your telescope, remember to cover it or or install a solar filter on it before using your solar-filter-equipped telescope to observe or image the sun.

All Astrozap Solar Filters use only high quality and safe materials. Astrozap offers 4 different types of solar filters. For pre-made solar filters, one size does not fit all!
Here are the variables you need to consider in choosing the right Astrozap solar filter for your particular telescope or binocular needs.


A. For pre-made Astrozap Solar Filters you need at least 1 inch of clear/unobstructed surface on the outside front of the optical tube(s) where the solar filter will slide on. Never mount a solar filter on anything other than directly to the optical tube. We do not recommend placing Astrozap pre-made Solar filters on telescopes or binoculars that have any obstructions on the 1-inch outside-front area of the optical tube (obstructions such as beveled plastic trim or mount fixture hardware can prevent safe mounting). It is especially important for Solar Filters to not leak sunlight – via stray light entering the optics or falling off altogether. Your equipment or more importantly, your eyes, could be harmed.

B. Telescopes need to be closed-tube type. Truss tube telescopes, even with cloth light shrouds, can leak sunlight and harm equipment or eyes. To be sure, check with your telescope manufacturer to see if your model is suitable for an accessory solar filter.


A. Astrozap offers Pre-Made solar filters, made to fit specific sizes (accommodating various makes and models) of telescopes or astronomy binoculars (meeting the basic requirements in #1 above), securely and safely. Pre-Made solar filters come with one or more plastic retaining screws, depending on the filter's size, that do not mar or scratch the finish on the optical tube. Astrozap Pre-Made Solar Filters are proudly made in the USA. Pre-Made solar filters from Astrozap come in three types:

I. Glass Full Aperture Solar Filters, compared to Off-Axis Solar Filters, allow substantially more light into the optics because the aperture size is close to the aperture size of the telescope or binocular. Glass Full Aperture Solar Filters are for visual observing or imaging and allow the best possible daytime viewing when there is minimal atmospheric turbulence (but remember that there is often atmospheric turbulence). If turbulence is present, a mask can be put over the end of the filter to effectively reduce the aperture. In effect, you can easily mimic an Off-Axis Solar Filter. (If you are fitting your binoculars, Astrozap only offers Binocular Glass Full Aperture Solar Filters).

II. Glass Off-Axis Solar Filters are for visual observing or imaging and block light into the telescope by only allowing light through a small portion of glass that is off center. By reducing the aperture, the image is not darker, but impaired visibility by daytime atmospheric turbulence is reduced. Also, it is noteworthy that Off Axis Solar Filters are less expensive than Full Aperture Solar Filters.
III. Baader Full Aperture AstroSolar™ Filters are made of flexible AstroSolar™ material for visual observing. With AstroSolar™, the sun appears in neutral white. Other films and some glass filters produce a blurry, bluish or reddish solar image, thereby cutting part of the spectrum. Especially with an orange sun, it is hard to see faculae regions which are visible predominantly in the blue wing of the spectrum.

B. Astrozap also offers Build-your-Own solar filters that come in one type: Baader AstroSolar™ Material. This is the same material as in the Pre-Made Baader Full Aperture AstroSolar™ Solar Filters. Baader Solar Filter material is for visual observing.


Here is how to find the right solar filter for your telescope or binocular. For Build-your-Own solar filters, skip to step C below. For Pre-Made solar filters, start with step A below.

A. Measure the front outside diameter, where the Astrozap Solar Filter will slide onto the outside front of the tube. The easiest and best way is to simply measure across the outside front of the tube in mm as shown below. Most of our measurements are in mm.

B. Measure the unobstructed distance on the front of the tube where the dew shield will slide on for a snug fit. Make sure you have at least 1 inch or 25mm unobstructed.

C. Under the SOLAR FILTERS main navigation button, click on the button link that goes to the type of solar filter you want to purchase and select the correct size. As an additional help for you, the glass solar filter product pages also show a table with sizes and some of the telescopes that each filter will fit. Not all telescope makes and models are included, but if you follow the “How to Choose the Right Astrozap Solar Filter” instructions, you will be able to find the right product.

D. Your choices under SOLAR FILTERS Astrozap home page link are grouped under the following button links:
- Telescope Pre-Made Solar Filters
> Glass Full Aperture Solar Filters
> Glass Off-Axis Solar Filters
> Baader AstroSolar™ Filters
- Binocular Pre-Made Full Aperture Glass Solar Filters
- Baader Solar Material to Build your Own Filters

E. If you still need help, simply contact us at and let us know what make and model telescope or binocular you are trying to fit. We are here to help!