Telescope Maintenance 54
the focal length of the lens until you are ready for prime focus photography with your Celestron Ultima
Telescope.
EYEPIECE PROJECTION
This form of celestial photography is designed for objects with small angular sizes, primarily the Moon and
planets. Planets, although physically quite large, appear small in angular size because of their great
distances. Moderate to high magnification is, therefore, required to make the image large enough to see any
detail. Unfortunately, the camera/telescope combination alone does not provide enough magnification to
produce a usable image size on film. In order to get the image large enough, you must attach your camera
to the telescope with the eyepiece in place. To do so, you need two additional accessories; a deluxe tele-
extender (#93643), which attaches to the visual back, and a T-ring for your particular camera make (i.e.,
Minolta, Nikon, Pentax, etc.).
Because of the high magnifications during eyepiece projection, the field of view is quite small which makes
it difficult to find and center objects. To make the job a little easier, align the finder as accurately as
possible. This allows you to get the object in the telescope's field based on the finder's view alone.
Another problem introduced by the high magnification is vibration. Simply tripping the shutter even
with a cable release produces enough vibration to smear the image. To get around this, use the camera's
self-timer if the exposure time is less than one second a common occurrence when photographing the
Moon. For exposures over one second, use the "hat trick." This technique incorporates a hand-held black
card placed over the aperture of the telescope to act as a shutter. The card prevents light from entering the
telescope while the shutter is released. Once the shutter has been released and the vibration has diminished
(a few seconds), move the black card out of the way to expose the film. After the exposure is complete,
place the card over the front of the telescope and close the shutter. Advance the film and you're ready for
your next shot. Keep in mind that the card should be held a few inches in front of the telescope, and not
touching it. It is easier if you use two people for this process; one to release the camera shutter and one to
hold the card. Here's the process for making the exposure.
1. Find and center the desired target in the view finder of your camera.
2. Turn the focus knob until the image is as sharp as possible.
3. Place the black card over the front of the telescope.
4. Release the shutter using a cable release.
5. Wait for the vibration caused by releasing the shutter to diminish. Also, wait for a moment of
good seeing.
6. Remove the black card from in front of the telescope for the duration of the exposure (see
accompanying table).
7. Replace the black card over the front of the telescope.
8. Close the camera's shutter.
Advance the film and you are ready for your next exposure. Don't forget to take photos of varying duration
and keep accurate records of what you have done. Record the date, telescope, exposure duration, eyepiece,
f/ratio, film, and some comments on the seeing conditions.
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