Thousand Oaks H-Alpha Prominence Filters (1.5 Angstrom Bandwidth)

For over twenty years we've manufactured the most popular white light filters in the world. With our white light filter, excellent views of sunspots and granulation are easily seen. In H-Alpha light, spectacular prominence activity can be seen at the limb. Flares are also visible on the surface along with the same white light details visible with our standard filters. The two part system is easy to use and can be setup in less than a minute. Each system includes an energy rejection filter (ERF) and 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-axis ERF. Refractors use a center axis as pictured below. ERF's can be purchased separately for additional telescopes. The purpose of the ERF is to increase the focal length 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 656.3. 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 length 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 length of f/20. An eight inch aperture f/10 Schmidt Cassegrain with the included 2.5" off-axis aperture ERF will have a working focal length of approximately f/30. The system may not work with some Newtonian and Dobsonian 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. It will not work with cameras or binoculars, however, it can be used photographically on telescopes with a standard prime focus/eyepiece projection adapter. The H-Alpha narrow band filter is sensitive to temperature and works best at 50 to 75 degrees Fahrenheit (10 to 24 C). For every 5 degree drop in temperature, the center wavelength will shift to the blue approximately 0.08 angstrom. The amount of shift in cold weather will be reduced since the small amount of energy transmitted through the ERF will help keep the filter warmer than the ambient temperature. An optional band heater is available. Temperatures above 75 degrees (24 C)* are not a problem since the tilting mechanism "tunes" the filter toward the blue. *The unit should not be subjected to temperatures above 110 degrees (43C).