What is a Solar Filter, and How Do You Use It?

June 12, 2023

What is a solar filter and how do you use it?

 

A solar filter is an astronomical filter that protects your eyes and equipment from the intense brightness of the Sun. They block or attenuate nearly all sunlight so you can safely observe solar phenomena such as sunspots, solar eclipses, and planetary transits. Solar filters are made from specialized materials that effectively block harmful ultraviolet (UV) and infrared (IR) radiation while allowing a tiny amount (0.00001%) of visible light to pass through.

Solar filters are essential. Our closest star, the Sun, is so bright that unfiltered sunlight can permanently damage your eyes and your telescope’s optics unless both are adequately protected.

Celestron EclipSmart products use filters constructed of either aluminized polyester film (Mylar) or glass. Our solar glasses, eclipse kits, and telescope solar filters use Mylar, while our binoculars and solar telescope use glass filters built into the optical path. All Celestron EclipSmart solar filter products feature Solar Safe filter technology and conform to the ISO safety standard, ISO 12312-2:2015(E), Filters for Direct Observation of the Sun.

 

 

 

Determining the Correct Celestron Solar Filter for your Telescope

Celestron offers 13 telescope solar filters that fit a wide variety of telescopes from 60mm to 8 inches in aperture. Each filter’s name lists the telescopes it works with for easy reference. Celestron’s solar filters are custom-fit to attach securely to the telescope’s front end. If you do not see your telescope model listed, you can determine which solar filter you need by measuring the interior dimension of your telescope’s front end. Compare your results to the solar filters’ spec charts. If you need assistance, you can contact our technical support team.

 

Solar filters for Refractors

Solar filters for Newtonian Reflectors

Solar filters for Schmidt-Cassegrain and EdgeHD                             

 

 

Installing a solar filter on to a Celestron telescope

Celestron carries two styles of solar filters, those that attach with thumbscrews and those that use hook-and-loop safety straps. The thumbscrew filters work with refractors, and the hook-and-loop filters work with Newtonian Reflectors, Schmidt-Cassegrains, and EdgeHD telescopes.

 

Thumbscrew solar filter

For filters with thumbscrews – Each filter has three thumbscrews evenly spaced around the filter. Place the filter over your telescope’s front cell and tighten the screws to ensure the filter does not move. Do not force the filter onto your telescope. If your filter does not fit, back out the thumbscrews to ensure they are not getting in the way.
hook and loop solar filter

For filters with hook-and-loop straps – Each filter comes with two hook-and-loop straps and four hook-and-loop squares. To set up the filter straps, first place the filter on the telescope. Affix two hook and loop squares to the filter’s outer hard plastic—one on each side. Next, affix two more hook-and-loop squares next to your first two squares on the telescope tube. Lastly, lay the hook-and-loop strap across the squares you laid down (see image for detail). Do not force the filter on your telescope. If your filter does not fit, ensure it is the right one for your telescope and nothing is impeding it on the telescope’s front cell.

 

 

Important Solar Safety Note

Inspect your filter before every use. Do not use and discard if damaged, torn, punctured, or separated from the frame in any way.