Center axis is only for refractor type telescopes
In H-Alpha light, at the limb, you’ll see spectacular views of the prominence activity, with the same white light details just as visible when using our standard filters. Our 2-part system can be set up in under 60 seconds and is easy to use.
You will receive an energy rejection filter (ERF) in every system as well as a HAU (H-Alpha filter unit) that comes with a tilting mechanism for fine tuning your scope. The HAU weighs only 7 ounces and comes in a compact size of 4 3/4″ long by 2″ diameter, making it extremely portable so that you can go to the best places for viewing needs.
The HAU attaches two different ways. One is between telescope back and star diagonal and the other is between star diagonal and eyepiece. All 1 1/4″ accessories will fit and the ERF fits over the telescope tube front easily and securely.
The design of the ERF is for a specific instrument, but otherwise, for all other telescopes, the HAU is the same. If your telescope has a secondary mirror obstruction, it will require an off-axis ERF while a center axis is used with refractors.
You can purchase ERF’s for additional telescopes so that the focal length can be increased while the energy is reduced as it enters the telescope and a “red light” showing as a narrow band enters. With the exception of the 656.28, all wavelengths are then blocked by the HAU completely.
The ERF’s and HAU must be used simultaneously. When the system is at f/20, you’ll get the best performance, which is compatible with Schmidt Cassegrains and most refractors. The ERF will increase the telescope’s effective focal length such as when using a 4 inch aperture f/10 refractor and the 2” center aperture that is included. With this setup, the focal length of the ERF will be f/20. An 8” aperture f/10 Schmidt Cassegrain combined with the 2.5″ off-axis aperture that is included, the working focal length of the ERF will be approximately f/30.
Using the prime focus eyepiece projection adapter and a standard T-Ring, astrophotography can be accomplished with great success.
In regards to using Newtonian and reflectors though, the system may not work well or not at all because the focus travel is too limited, taking into consideration that the focus is extended out 3 1/8″ and the minimum of f/15 is not possible. As such, systems for these telescopes are not available through us.
Note: The Filter Aperture references the aperture that is needed for the ERF. You may reach out to Spectrum Telescope for assistance in determining the proper size needed. You will need to have the type of Telescope you’re using as well as the Clear Aperture, F Ratio, and Outer Diameter when you call so that we may determine the proper calculation.

Attention
System does not work for Newtonian reflectors the focus travel is to limited. (Focus is extended out 3 1/8’’) with the minimum is f/15 cannot be achieved. Spectrum Telescope does not offer a system for Newtonian reflectors.