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Spectrum Full Aperture Glass Solar Filter for 48 mm - 54 mm OD Telescopes - ST225G

SKU: SPR-ST225G
To ensure that the solar filter you buy will fit properly, please take a few moments and measure the outside diameter of your telescope, spotting scope or binoculars before you order. Remember, the solar filter needs to fit snugly around the front of the tube assembly that holds the optics. If the filter is slightly larger than its diameter, the filter can be made to fit by the addition of self-stick felt spacers to the inside of the cell. However, if the filter is too small it will not fit, and that would be a shame. So please, measure before you order. Thanks.

Spectrum Glass Solar Filter for 48 mm - 54 mm OD Telescopes


This Spectrum Full Aperture Glass Solar Filter fits small refractors, view finders, cameras, spotting scopes, and binoculars.

This 57 mm ID Full Aperture Glass Solar Filter from Spectrum Telescope lets the maximum amount of light possible pass through to your telescopes safely, providing peace of mind when directly viewing the Sun. When observing, the ST225G Solar Filter uses your telescope's full aperture, permitting the best achievable daytime viewing with extremely low atmospheric instability. When instability does take place, however, a mask can be placed over the filter to adequately reduce the aperture.

This premium solar filter features felt padding and offers impressive durability. The aluminum cell is centered and uses nylon thumb screws to fit to the end of the optical tube. Made from high quality, extensively tested hand-picked glass with reflective coatings. The sun has a pure yellowish-orange look when directly observed using this filter.

To protect this filter from damage during shipping, it comes shielded in plastic in a foam-lined box. This box can also serve as a means to store the filter when it's not being used. Includes thorough instructions on proper use and care for your unit.

Spectrum ST225G Full Aperture Glass Solar Filter Specifications


  • Inside Diameter: 2.25" (57 mm)
  • Clear Aperture Diameter: 1.75" (44 mm)
  • Fits instruments with an outside diameter range of 1.875" - 2.125" (48 mm - 54 mm)

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).