Celestron CR-150 HD - Manual (Page 48)

48 • Celestial Photography
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 a projection lens in place.
This can be accomplished with the use of the 2x barlow lens / T-adapter. Slide the 1
1/4" barrel of the barlow lens directly into the focuser and secure with the chrome set
screw. Then attach the T-ring for your particular camera make (i.e., Minolta, Nikon,
Pentax, etc.) and camera body to the T-adapter.
Because of the higher magnifications during projection photography, the field of
view is smaller which makes it more 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 higher 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.
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.
Projection Photography Projection Photography Projection Photography Projection Photography Projection Photography