Celestial Photography • 49
This form of celestial photography is designed for objects with small angular sizes,
primarily the planets and individual lunar features. 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 tele-extender
(#93643), which attaches onto 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 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 table 7-2).
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.
The following table lists exposures for eyepiece projection with a 10mm eyepiece.
All exposure times are listed in seconds or fractions of a second.
Eyepiece Projection
