11
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 viewfinder 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.
The following table lists exposures for eyepiece projection with a 10mm eyepiece. All exposure times are listed
in seconds or fractions of a second.
Planet
ISO 50
ISO 100
ISO 200
ISO 400
Moon
4
2
1
1/2
Mercury
16
8
4
2
Venus
1/2
1/4
1/8
1/15
Mars
16
8
4
2
Jupiter
8
4
2
1
Saturn
16
8
4
2
The exposure times listed here should be used as a starting point. Always make exposures that are longer and
shorter than the recommended time. Also, take a few photos at each shutter speed. This will ensure that you get
a good photo. It is not uncommon to go through an entire roll of 36 exposures and have only one good shot.
NOTE:
Don't expect to record more detail than you can see visually in the eyepiece at the time you are
photographing.
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.
Table 3-2
Recommended exposure time for photographing planets.
