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Spectrum Full Aperture Glass Solar Filter for 51 mm - 57 mm OD Telescopes - ST250G

SKU: SPR-ST250G
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, viewfinders, cameras, spotting scopes, and binoculars as well as the Celestron 9x50 finder and William Optics 7x50 finder.

This Full Aperture Glass Solar Filter from Spectrum Telescope with 60 mm ID allows the maximum quantity of light possible to transmit to your telescope for a safe solar observing experience. The entire aperture of your optical tube is used when viewing for the highest potential daylight observing with very low atmospheric fluctuation. When these fluctuations do take place, a mask can be installed over the filter to decrease the aperture.

This sturdy premium solar filter has been designed using superb quality, hand-selected glass with reflective coatings that have been extensively tested. The aluminum cell is centered and fixes to the end of the telescope with the help of felt padding and nylon thumb screws. The sun appears in its organic yellowish-orange state when viewed directly through a telescope with this filter attached.

To avoid any possible damage while in transit, this filter is wrapped in plastic and shipped in a foam-lined box. This box also provides convenient storage when the filter is not in use. Includes full comprehensive instructions on how to properly use and care for your unit.

Spectrum ST250G Full Aperture Glass Solar Filter Specifications


  • Inside Diameter: 2.5" (60 mm)
  • Clear Aperture Diameter: 1.75" (44 mm)
  • Fits instruments with an outside diameter range of 2" - 2.25" (51 mm - 57 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).