Alan Gee Telecompressor Mark II





Alan Gee Telecompressor Mark II

The Alan Gee Mark II is made with typical Baader Planetarium attention to detail and flexibility by design.  Designed by Roland Christen, the optical configuration consists of a matched, wide air-spaced doublet, utilizing lenses that are precision polished to the very edge, and anti-reflection coated with the finest 7 layer multi-coatings available today (reflections per surface are less than 0.2% !).  The lenses are individually centered and painstakingly mounted into the precision cell.  The extra-large 35mm clear optical aperture and lens cell design maximizes the field size.  The cell itself is unique. The long extremely thin-wall aluminum tube surfaces are sharp V-threaded and blackened, to reduce stray light reflections.  The telecompressor assembly actually consists of 4 threaded pieces; the lens cell, two 19mm long removable spacer sections, and a flanged end-ring (plus a thin spacer ring used in some configurations).  The OD of the lens cell and spacers is 37.5 mm, permitting the AGII to insert up inside the baffle tube of 8" and larger SCTs.  By using combinations of these pieces, along with varying the placement in the optical path, you can now utilize the Alan Gee in a wide variety of visual and imaging configurations that have never been possible with any other telecompressor (see the section below for suggested configurations).  Please contact us if you have a need for a configuration not shown - we have been able to come up with a way to mount the AGII in practically every situation.

Until now, SCT focal reducers were designed primarily for imaging or single eyepiece use, and lacked the necessary focal length and positioning flexibility to work with binocular viewers.  The Alan Gee Mark II has been designed to work perfectly in concert with the Celestron and Baader Planetarium Binoviewers * (including the Baader/Zeiss Giant Binocular Viewer).  Now, you can turn your SCT into the ultimate large aperture wide field binocular telescope!  Imagine the stunning wide field binocular views that your telescope will deliver (up to a 1.2 field in a C8 or 0.7 in a C14 - using the Baader/Zeiss Giant Binocular Viewer, that's almost a 3X improvement in field area!).  Now, not only will large deep sky objects now fit within the field of view, but even the entire Moon can be comfortably viewed with two eyes.

* Please Note:  The close coupling required for the telecompressor to reach focus with binoviewers limits it's use to only the Baader/Zeiss and Celestron binoviewers. 

Imaging Use:  Of course, the Alan Gee Telecompressor Mark II also delivers the ultimate photographic image.  Whether for film or CCD imaging, this telecompressor will produce a sharp, flat field, with the minimum vignetting possible. Coverage for 35mm photography is superb, delivering the sharpest wide-field images possible from your SCT.   Click on the image below, for an idea of a typical image, flat-field, and CCD setup (image courtesy of R.Crouch).

Product Pricing

Ordering Information

Visual and Imaging Configurations

The Alan Gee Telecompressor Mark II can be configured in quite a number of ways, for both imaging (film/CCD) and visual uses.  The AGII is designed for a nominal back-focus distance of 121mm, as measured from the rear face of the lens assembly cell to the focal plane.   Listed below are some of the most common and useful configurations.  In order to make full use of the Alan Gee telecompressor, some configurations make use of a number of additional components.  These components are shown in the schematic images linked to below, and are individually detailed in Eyepiece Adapters, Rings.  For detailed dimensional specs on Astro T-2 components, see the ASTRO T-2 System Specs.

- Visual

For visual use, both single-eyepiece and binocular viewing are supported by the Alan Gee telecompressor.  For single-eye views, you can configure the telecompressor to work with 1 diagonals and eyepieces, enabling you to reduce magnifications and significantly increase the field of view of all  your existing eyepieces.  For a typical single eyepiece schematic, see the 1 Layout.

For two-eye binoviewing, the Alan Gee can be mounted in front of either the Celestron-Baader binocular viewer or Baader/Zeiss Giant Binocular Viewer.  The very widest field views will be produced by the larger clear aperture of the Baader/Zeiss viewer.  Here, the unique design of the Alan Gee enables full-field performance with all 1 eyepieces.  For schematics of how to configure the Alan Gee with these binocular viewers, see the Celestron Binocular Viewer Layout and the Baader/Zeiss Binocular Viewer Layout

- Imaging

For 35mm photography, the telecompressor is simply inserted up inside the SCT baffle tube, and the Short T-Adapter (plus the included spacer ring) threaded onto the SCT back (or for 10+ SCTs, onto their standard thread reducing plate) to retain the Alan Gee telecompressor.  This configuration results in the desired f/5.9 focal ratio (for an f/10 scope).  For a visual schematic of this configuration, see the 35mm Photographic Layout.  

Other configurations allow you to mount the AGII inside a traditional 2" nosepiece, for insertion into the 2" fine focusers now in use on many  SCTs.  It is also possible to mount the AGII directly onto a 2" filter, permitting the use of filters in the optical train (requires one #T2-29, and two #T2-25C).

For CCD imaging, a similar configuration (to 35mm film) is used.  However, several of our other Baader T-2 components provide some very useful additions which can allow you to quickly switch between CCD camera and other accessories (i.e., focusing eyepieces).  For a visual schematic of this configuration, see the CCD Imaging Layout.


last updated 04/11/09


HOME  |  Contact Us by Email (

Copyright 2007 Alpine Astronomical, LLC.  All Rights Reserved.