Handbook for the SXVR-M26C Issue 1 March 2010
27
1) Dust can be deposited on either the optical window (not a big problem to cure), or
on the CCD faceplate (very difficult to eliminate entirely). When small particles
collect on the window they may not be noticed at all on deep sky (small F ratio)
images, as they will be very much out of focus. However, if a powerful contrast boost
of the image is carried out, they may well begin to show as the shadow ‘Do-nuts’
mentioned earlier. Images taken with a large F ratio optical system are more likely to
be affected by such dirt, owing to the smaller and sharper shadows that they cast. A
light polluted sky will also make these marks much more obvious. There is no great
difficulty in removing such particles on the outside surface by the careful use of a lens
cleaning cloth, ‘lens pen’, or ‘air duster’ and so you should have little trouble with
this aspect of maintenance. Dust on the CCD faceplate is a much greater nuisance, as
it casts very sharply defined and dark shadows and it entails dismantling the camera to
get rid of it! To clean the CCD you will need a good quality lens cloth (no silicone) or
tissues and some high-grade acetone or isopropyl alcohol. A very suitable cloth is the
‘Micro-Fibre’ type marketed by PENTAX etc., and suitable alcohol is available from
Maplin or Radio Shack etc. as tape head cleaning fluid. Most pharmacist shops will
have small bottles of pure acetone. A bright light and a strong watchmakers eyeglass
will also be found to be essential.
Procedure:
1) Disconnect the lead from the camera head and remove it from the telescope. Place
it on a table with the optical window facing downward.
2) Remove the two M3 screws and the M8 nut from the camera back plate and ease
the plate out of the camera body. Unplug the fan lead from the camera PCB.
3) Withdraw the body cylinder and unscrew the two top spacer pillars from the PCB.
Now gently lift the PCB off the 20 way connector NOTING THE ORIENTATION
OF THE BOARD for correct replacement later. Now remove the lower two spacers
from the heat sink plate assembly.
4) The camera heat sink assembly can now be lifted away from the camera front
barrel and the CCD will be exposed. Note that a layer of white heat-sink compound is
applied to the periphery of the heat sink disc and this should be left undisturbed by
subsequent operations.
5) You can now closely examine the CCD faceplate under the spotlight using the
watchmaker's glass when any dust motes will show clearly. If there is only an odd
particle or two and the CCD is otherwise clean, carefully brush away the dust with a
corner of your lens cloth. A smeared or very dusty CCD will need a few drops of
alcohol to clean thoroughly and you may have to make several attempts before the
surface is free of contamination. One gentle wipe from one end to the other, with no
return stroke, will be found to be the most effective action. DO NOT rub vigorously
and be very careful to avoid scratching the window.
6) Before re-assembly, make certain that the inside surface of the front window is also
clean, and then carefully replace the camera front barrel and screw it into place. (If the
heat sink seal is disturbed, renew it with fresh compound before reassembling).
7) Replace all the camera parts in reverse order and the job is done.
Dealing with condensation:
(28 pages)
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