Hydrogen Alpha Prominence Filter: £948.77

9" - 10" Center Axis

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 3/4In long x 2In diameter and weighs approximately 7oz. It attaches between telescope back and star diagonal or between star diagonal and eyepiece and accepts standard 1 1/4In 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 2In center aperture ERF will have a working focal length of f/20. An eight inch aperture f/10 Schmidt Cassegrain with the included 2.5In 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 focus\eyepiece projection adapter.

Please note that stock levels do fluctuate so please call or email to check today's stock before placing your order.

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