Celestron CGEM 1100 User Manual
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Once you have mastered the technique, experiment with different films, different focal length eyepieces, and even different
filters.
Long Exposure Prime Focus Photography
This is the last form of celestial photography to be attempted after others have been mastered. It is intended primarily for
deep sky objects, that is objects outside our solar system which includes star clusters, nebulae, and galaxies. While it may
seem that high magnification is required for these objects, just the opposite is true. Most of these objects cover large angular
areas and fit nicely into the prime focus field of your telescope. The brightness of these objects, however, requires long
exposure times and, as a result, are rather difficult.
There are several techniques for this type of photography, and the one chosen will determine the standard accessories needed.
The best method for long exposure deep sky astrophotography is with an off-axis guider. This device allows you to
photograph and guide through the telescope simultaneously. Celestron offers a very special and advanced off-axis guider,
called the Radial Guider (#94176). In addition, you will need a T-Ring to attach your camera to the Radial Guider.
Other equipment needs include a guiding eyepiece. Unlike other forms of astrophotography which allows for fairly loose
guiding, prime focus requires meticulous guiding for long periods. To accomplish this you need a guiding ocular with an
illuminated reticle to monitor your guide star. For this purpose, Celestron offers the Micro Guide Eyepiece (#94171) Here is
a brief summary of the technique.
1.
Polar align the telescope.
For more information on polar aligning, see the Polar Alignment section earlier in the manual.
2.
Remove all visual accessories.
3.
Thread the Radial Guider onto your telescope.
4.
Thread the T-Ring onto the Radial Guider.
5.
Mount your camera body onto the T-Ring the same as you would any other lens.
6.
Set the shutter speed to the "B" setting.
7.
Focus the telescope on a star.
8.
Center your subject in the field of your camera.
9.
Find a suitable guide star in the telescope field. This can be the most time consuming process.
10. Open the shutter using a cable release.
11. Monitor your guide star for the duration of the exposure using the buttons on the hand controller to make the needed
corrections.
12.
Close the camera's shutter.
When getting started, use fast films to record as much detail in the shortest possible time. Here are proven recommendations:
Ektar 1000 (color print)
Konica 3200 (color print)
Fujichrome 1600D (color slide)