Starlight Xpress SXVF-H9 - Manual (Page 19)

Handbook for the SXVF-H9 Issue 1 May 2007
19
As a finishing touch, the application of a Median filter or a Weighted Mean Low Pass
filter can be useful to smooth out the high frequency noise after a strong Unsharp
Mask.
As with deep-sky images, it is advantageous to sum planetary images together to
improve the signal to noise ratio. In this case, the ‘averaging’ option should always be
used, or the result is likely to exceed the dynamic range of the software and saturate
the highlights. Aligning the images is always something of a problem, as there are
rarely any stars to use when imaging the planets, but Jupiter’s satellites can be useful
reference points. Otherwise, you will have to find a well-defined feature on the planet,
or estimate where the centre of the disk is located. Some more sophisticated software
can automatically align planetary images and you may find these programs to be very
useful.
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Using the add-on autoguider:
A very useful accessory is the add-on autoguider head, which takes its power and
control signals directly from the SXV camera, via the 18 way socket on its rear panel.
The autoguider is only 1.25” in diameter and has a video style ‘CS’ mount thread in
its nose, so video lenses may be attached. The guider may be used with either an off-
axis prism assembly mounted in front of the SXV camera, or with a separate guide
telescope, rigidly mounted alongside your imaging telescope. I personally use it with
a 70mm aperture, F10, inexpensive refractor as a guide ‘scope, but a shorter focal
length lens will make more guide stars available in any given region of sky (See the
picture below).
To use the autoguider, first orient it so that the connector plug is roughly parallel to
the declination axis of your mount. This is not absolutely essential, as the training
routine will learn the angle of the head and compensate for it, but it is easier to
understand the motion of the guide star if the guider frame is aligned with the RA and
Dec axes. Now connect the head to the SXV camera, using the 18 way connector lead,
including the port divider box, if it is to be used.
The recommended way of connecting the autoguider output to the mount is to use an
RJ11 telephone lead between the socket on the SXV camera and the autoguider input
of your mount. This output is ‘active low’ (i.e. the control relays pull the guider inputs
down to zero volts when applying a guide correction) and matches most of the
autoguider inputs on commercial mounts. If ‘active high’ inputs are needed, or a very
low control voltage drop is essential, then you will need to add a Starlight Xpress
‘relay box’ between the guider output and the input to the mount. Please contact your
local distributor if a relay box is required. Some mounts (Vixen, for example) use a
similar guider input socket, but have re-arranged connections. Details are given on our
web pages at the end of the ‘STAR2000’ section.