Specifications

Section 3 - At the Telescope with a CCD Camera
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3.9.5. Auto Grab
The Auto Grab command allows you to take a series of images at a periodic interval and log the
images to disk. This can be invaluable for monitoring purposes such as asteroid searches or
stellar magnitude measurements. You can even take sub-frame images to save disk space if
you don't need the full field of view.
3.9.6. Color Imaging
Since all SBIG cameras are equipped with monochromatic CCDs, discriminating only light
intensity, not color, some provision must be made in order to acquire color images. The
Research Series cameras have an internal filter carousel that will accept filters for color imaging.
The color filter wheel allows placing of interference filters in front of the CCD in order to take
multiple images in different color bands. These narrow band images are then combined to
form a color image. With the SBIG system, a Red, Green and Blue filter are used to acquire
three images of the object. The resulting images are combined to form a tri-color image using
CCDOPS, CCDSoftV5 or third party software.
Color imaging places some interesting requirements on the user that bear mentioning.
First, many color filters have strong leaks in the infrared (IR) region of the spectrum, a region
where CCDs have relatively good response. If the IR light is not filtered out then combining
the three images into a color image can give erroneous results. If your Blue filter has a strong
IR leak (quite common) then your color images will look Blue. For this reason, SBIG
incorporates an IR blocking filter stack with the three color band filters.
Second, since you have narrowed the CCD's wavelength response with the interference
filters, longer exposures are required to achieve a similar signal to noise compared to what one
would get in a monochrome image with wide spectral response. This is added to the fact that
tri-color images require a higher signal to noise overall to produce pleasing images. With black
and white images your eye is capable of pulling large area detail out of random noise quite
well, whereas with color images your eye seems to get distracted by the color variations in the
noisy areas of the image. The moral of the story is that while you can achieve stunning results
with CCD color images, it is quite a bit more work.