note that cameras with smaller pixels may be binned 2x2 or 3x3 to create larger pixels and
expand the useful range of the camera. For example, an STXL-16000 with 7.4 micron pixels can
be binned 2x2 to give 14.8 micron pixels. The overall field of view of the CCD does not change
however, and a camera with larger pixels and a larger field of view might be preferable if it will
not be used on shorter focal length instruments.
1.16. Camera Field of View
The field of view that your camera will see through a given telescope is determined by the focal
length of the telescope and the physical size of the CCD chip. This also has nothing to do with
the number of pixels.
Through the same
telescope, a CCD that has
512 x 512 pixels at 20
microns square will have
exactly the same field of
view as a CCD with 1024
x 1024 pixels at 10
microns square even
though the latter has four
times as many pixels.
One can vary the focal
length to vary the field of
view. Using a focal
reducer to shorten the
focal length will increase
the field of view (and
make the image brighter in the process). Using a barlow or eyepiece projection to effectively
lengthen the focal length of the telescope will decrease the field of view (and make the image
dimmer in the process). In order to determine the field of view for a given CCD, note the CCD's
length and width dimensions in millimeters (from the
camera specifications) and use the following formula for
determining the field of view for that CCD through any
telescope:
(135.3 x D ) / L = Field of View in arcminutes
where
D
is the length or width dimension of the CCD in
millimeters, and
L
is the focal length of your telescope in
inches. So, for example, if you wanted to know the field of
view of the new STL-4020M camera when attached to a 5"
F/6 telescope you would first determine the focal length of
the telescope by multiplying its aperture, 5 inches, by its
focal ratio, 6, to get its focal length, 30 inches. The CCD
dimensions are 15.2 x 15.2 mm. To calculate the field of
view multiply 135.3 x 15.2 = 2,057 and then divide by 30 = 68.6 arcminutes. By way of
comparison, the field of view of the STXL-16803 through the same telescope would be 135.3 x
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