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Spectrum Full Aperture Glass Solar Filter for 98 mm - 105 mm OD Telescopes - ST425G
Spectrum Glass Solar Filter for 98 mm - 105 mm OD Telescopes
This Spectrum Full Aperture Glass Solar Filter fits the following instruments:
- Meade ETX-90
- Celestron NexStar 60/80/80GT, FirstScope 90 EQ
- Orion StarMax 90, Apex 90
- Stellarvue Nighthawk APLANAT, Nighthawk Next Generation with Dew Shield, SV80/9D with Dew Shield
- Questar 3.5"
- William Optics ZS80 II ED, Megrez 80
This Full Aperture Glass Solar Filter from Spectrum Telescope with 108 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.
When directly viewed through this long-lasting premium solar filter, the sun has an organic yellowish-orange appearance. The aluminum cell on this filter is centered and attaches to the end of the optical tube with felt padding and nylon thumb screws. The hand-selected, superb quality glass used in the design of the ST425G Solar Filter has reflective coatings that have been extensively inspected.
This filter is encased in plastic and then placed in a foam-lined box for shipping to prevent damage in transit. When the filter is not in use, the box can be used as a easy means for storage. Detailed instructions on proper use and care of your filter are included.
Spectrum ST425G Full Aperture Glass Solar Filter Specifications
- Inside Diameter: 4.25" (108 mm)
- Clear Aperture Diameter: 3.5" (90 mm)
- Fits instruments with an outside diameter range of 3.875" - 4.125" (98 mm - 105 mm)
In order to assure a proper fit, please be sure to measure the outside diameter of your telescope before committing to purchase a specific solar filter as telescope specifications may be modified with subsequent versions due to re-designs, etc.
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).