Although Baader officially calls this a T-ring, this bayonet offers far more. The Baader Protective T-Ring allows Canon EOS cameras to attach to standard 2" eyepiece holders. It is optimized for full-frame sensor cameras (such as the Canon EOS 5D), but can be used with any EOS camera. Since it has a wider clear aperture than the restrictive T-ring (42 mm) size, it does not vignette the light cone of fast optics. Whereas it utilizes a 48 mm thread, it also includes a 48 mm to 42 mm adapter for using traditional T-thread accessories.
Baader has optimized the fit and tolerances between the camera bayonet and T-ring. This ensures that its connection to the EOS camera is wobble-free and has no lateral play, thus guaranteeing a stable image platform for long exposures.
One of the unique features of this “T-ring" is that it accepts internal filters (optional). Baader unmounted 50.4 mm or 50.8 mm and Baader low-profile 2" mounted filters can be installed internally.
*H-alpha filter preinstalled. Please note that using the H-alpha filter requires that the camera has been modified and its internal filter replaced with an expanded range filter. Modification is not needed for the Canon 20Da and 60Da cameras.