Solar Spectrum H-alpha filters require parallel light with a ray path of at least f/30. This is achieved by a focal length with our telecentric systems (and possibly also by dimming the lens with the iris). Because of the focal length extension in many telescopes the sun is not completely visually apparent when using eyepieces with f = 30 to 35 mm.
Note: both Baader Solar Spectrum Telecompressors are mounted straight onto the Solar Spectrum body rear end and reduce the f/30 ratio by a factor of 0.4x. As a result, a much larger portion of the solar surface comes into view, depending on the size of the Etalon mounted inside the Solar Spectrum filter.
A telecompressor is used to adjust the focal length to possibly poor seeing conditions and / or enlarging the field for photographic- or webcam applications.
To attach the telecompressor use our 2″ Universal flange (# 295 8240); it gets attached with four screws directly onto the filter housing (see illustration), the telecompressor is mounted directly into the 2″ thread of the universal flange. The main thread of the compressor also is a 2″ male thread. This can be changed if necessary with parts from our T-2 accessories system either to a T-2 internal or external thread.