Thousand Oaks Optical - 6 inch H-Alpha Filter CENTER-AXIS

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 656.28. 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 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. Astro-photography
can be done using a standard T-Ring & prime focuseyepiece projection adapter.

The system does not work well, if at all with 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. We do not offer systems for these telescopes.

AT TIME OF CHECK OUT - Please specify telescope brand, focal length and outside diameter
measurement of telescope tube.
The cost of filter is based on the aperture of your instrument.