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 1.2º field in a C8 or 0.7º 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.
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).
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
For detailed dimensional specs on Astro T-2 components, see the
ASTRO T-2 System Specs.
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 1¼” 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
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
1¼” eyepieces. For schematics of how to configure the Alan Gee with these
binocular viewers, see the
Celestron Binocular Viewer Layout
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