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Section 5 - Advanced Imaging Techniques
Page 33
5. Advanced Imaging Techniques
With practice, you will certainly develop methods of your own to get the most from your CCD
camera. In this section we offer some suggestions to save you time getting started in each of
the different areas outlined below, but these suggestions are by no means exhaustive.
5.1. Lunar and Planetary Imaging
When imaging the moon using most focal lengths available in astronomical telescopes, you will
note that the moon's image typically fills the CCD. The image is also very bright. The best
way to image the moon is to use neutral density filters to attenuate the light.
You may also try an aperture mask to reduce the incoming light. If you feel that an
aperture mask reduces resolution to an unacceptable degree, consider using a full aperture
solar filter. This will result in an optimum exposure of only a few seconds. Another way to
reduce the incoming light is to increase the effective focal length of your telescope by using a
barlow lens or eyepiece projection. This is very desirable for planetary imaging since it also
increases the image size.
5.2. Deep Sky Imaging
Ordinarily, with telescopes of 8" aperture or larger, a ten second exposure in focus mode, with
a dark frame subtracted, will show most common deep sky objects except for the very faintest.
This is a good starting point for finding and centering deep sky objects. If you find ten seconds
to be insufficient, a one minute exposure will clearly show nearly any object you wish to image,
particularly if 2x2 or 3x3 binning is selected. Using the Grab command, exposures of five
minutes will generally give you a clear image with good detail. Of course, longer exposures
are possible and desirable, depending on your telescope's tracking ability or your desire to
guide. Once you have determined the longest exposure possible with your particular drive
error, try Track and Accumulate exposures of a duration less than your measurable error. We
have found that exposures of thirty seconds to two minutes are best depending on the focal
length of telescope one is using. With the self guiding feature of the ST-7E/8E/9E/10E one
can take long integrations while the internal tracking CCD guides the telescope.
We highly recommend that you initially pursue deep sky imaging with a fast telescope,
or focal reducer to produce a final F number of F/6.3 or faster at the CCD. The sensitivity
advantage is considerable!
5.3. Terrestrial Imaging
An optional accessory for the SBIG cameras is the camera lens adapter. These accessories are
made to accommodate most popular camera models. You may attach a camera lens in place of
your telescope and use the CCD camera for very wide angle images of the night sky or for
terrestrial views in daylight. Begin with a tenth second exposure at f/16 for scenes at normal
room light and adjust as necessary for your conditions.
5.4. Taking a Good Flat Field
If you find that flat field corrections are necessary due to vignetting effects, CCD sensitivity
variations, or for more accurate measurements of star magnitudes, try either taking an image of