Starlight Xpress SXVR-H18 - Manual (Page 22)

Handbook for the SXVR-H18 Issue 1 March 2010
22
If the stars are not circular, you may need to alter the guiding parameters, or
investigate the rigidity and drive performance of your mount. A lot of information
can be deduced by watching the behaviour of the guide star in the guider frame. If
it is continually moving between two locations, either side of the green cross, then
the RA or Dec pixels per second value is set too low. The higher these values are
set, the gentler the guiding becomes. Too low a value will cause an over-
aggressive correction to be made and result in oscillation of the star position
between two points.
Another source of guiding errors can be a too accurately balanced telescope
mount! Good balance can result in the telescope mount ‘bouncing’ between the
gear teeth as corrections are made. A simple fix is to add a weight of about 0.5kg
(1 pound) on the eastern end of the declination axis, so that there is always some
pressure acting against the gear teeth.
Getting a good result from an autoguider will often entail a lot of detective work
to eliminate the sources of gear error, telescope flexure, mirror shift etc., but the
final result is well worth the effort!
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Camera maintenance:
Very little maintenance is needed to keep the SXVR-H18 in excellent operating order,
however two problems, which are common to all CCD equipment, are likely to show
up on occasion. These are dust and condensation.
Removing Dust:
1) Dust can be deposited on either the optical window (not a big problem to cure), or
on the CCD faceplate (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. There is no great
difficulty in removing such particles on the outside surface by the careful use of a lens
cleaning cloth 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 isopropyl alcohol. A very suitable cloth is the ‘Micro-Fibre’
type marketed by PENTAX etc., and suitable alcohol is available from TANDY
(Radio Shack) etc. as tape head cleaning fluid. A bright light and a strong
watchmakers eyeglass will also be found 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.