Each system includes an energy rejection filter (ERF) and an H-alpha filter unit (HAU) with a tilting (fine-tuning) mechanism. The HAU is a compact 4-3/4″ long x 2″ diameter and weighs approximately 7oz. It attaches between telescope back and star diagonal or between star diagonal and eyepiece and accepts standard 1-1/4″ accessories. The ERF fits over the front of the telescope tube. The HAU is the same for all telescopes, however, the ERF is designed for use with a specific instrument. Telescopes with a secondary mirror obstruction require an off-axes ERF. Refractors use a center axis as pictured. ERF’s can be purchased separately for additional telescopes. The purpose of the ERF is to increase the focal ratio and reduce the energy entering the telescope while allowing a narrow band of “red light” to enter. The HAU completes the blocking of all wavelengths except 656.28. The HAU and ERF MUST be used together.
The system works best at f/15 and above and is compatible with most refractors and Schmidt Cassegrains. The effective focal ratio of the telescope is increased with the ERF. Example: A four-inch aperture f/10 refractor with the included 2″ center aperture ERF will have a working focal ratio of f/20. An eight-inch aperture f/10 Schmidt Cassegrain with the included 2.5″ off-axes aperture ERF will have a working focal ratio of approximately f/30. Astro-photography can be done using a standard T-ring & prime focus\eyepiece projection adapter.
The system does not work well, if at all, with Newtonian and reflectors since the focus travel may be too limited (the focus is extended out 3-1/8″) or the minimum of f/15 cannot be achieved. We do not offer systems for these telescopes.