H-Alpha (.9 Angstrom) http://www.thousandoaksoptical.com/halpha.html 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 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-axis 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. Solar Filters ("White Light") http://www.thousandoaksoptical.com/solar.html Jamie B "Instead of the John, I call my bathroom the Jim... That way it sound better when I say I go to the Jim first thing every morning." _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options".

-----Original Message----- From: Utah-Astronomy [mailto:utah-astronomy- bounces@mailman.xmission.com] On Behalf Of william baker via Utah- Astronomy Sent: Wednesday, April 20, 2016 12:26 PM To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Subject: [Utah-astronomy] H Alpha filer

A quick question to two to the open group. What type of H Alpha filer would be best for a 10 Dob? If you have a suggestion, why would you suggest that make or model? Thanks Bill _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy

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