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TRACKING
For photographing DSOs good tracking is essential if you want to extract
any detail.
If you plan to take exposures (subs) longer than 15 seconds (this minimum duration depends
on focal length) if tracking is bad the image gets "smudged" across the CCD chip
(evidenced by star trailing in subs).
For DSOs ideally you want the image to stay over the same pixels for the entire duration
of each exposure. This requires either 1) short focal length 2) Short exposures or 3) good
tracking and polar alignment.
Some drift is acceptable because the stacking software builds up an "average"
image and reduces the effects of the smudging, but if there is no drift in the first place
then it will only help with the "clarity" of the image detail.
That said there is some advantage in letting the image drift very slowly (one pixel per
two or three subs) because by moving the image across to a different set of pixels it can
help with averaging out the effect of noise in the pixels.
Planets are less sensitive to tracking because they are brighter. The permissible drift is
faster because the exposures are a lot shorter so each very short exposure will keep the
image on the same pixels for all (or for almost all of) each exposure.
With the moon the exposures are so short that you can use a CCD camera with no tracking
and still get acceptable results by stacking in software. This could be by just holding
the camera up to the eyepiece of a Dob and taking a happy snap, or by fitting the camera
with a telephoto (>150mm) SLR lens and sitting it on a fence post.
For all of the above reasons a sensitve CCD camera with a short focal length (<50mm)
SLR fast lens (f/2.8 or faster) can take 15 second subs of widefields (eg. the Milky Way)
on a tripod with no tracking required.
I highly recommend starting with the craters on the moon.
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