Starlight Xpress SXV-M5C - Manual (Page 21)

Handbook for SXV-M5C Issue 1 August 2004
21
box and cables are available as an accessory and may be chained in series with the
autoguider cable, when the guider is in use, or may be used on its own.
The two serial connections are in the form of standard RS232 PC style plugs and
provide TX, RX and Ground connections at RS232 levels. Access is via commands
sent through the USB connection and, at the time of writing, is limited to any serial
controls that are provided by the SXV software. It is expected that many more
functions will be added as the software is upgraded.
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STAR 2000
The SXV-M5C may be used with our patented self-guiding system ‘STAR 2000’.
This can greatly ease the process of recording long exposure deep-sky images.
Using ‘STAR 2000’ self-guiding with the SXV-M5C
How S.T.A.R. 2000 works:
S.T.A.R. 2000 is a unique and patented method of automatically controlling your
telescope drives, while capturing a long exposure image with your Starlight Xpress
CCD camera. Unlike off-axis guiding devices and dual-CCD self-guiding cameras,
S.T.A.R. 2000 can guide on almost any object, which is visible within the CCD
frame! You have the entire CCD field of view to choose from and can even select a
slowly moving target, such as a comet nucleus, or asteroid, to guide on during the
exposure.
The principle of S.T.A.R. is based on the special CCD structure of the chips used in
our SXV_M5, M7 and M9 cameras and it cannot be used with ‘full frame’ CCDs,
such as the popular Kodak devices. It is also incompatible with our HX516 camera.
The M5, M7 and M9 use ‘Interline Interlaced’ CCD chips, which are constructed with
each pixel split into two vertically stacked halves. Each half can be ‘read out’
independently, so it is possible to integrate a long exposure on one field of half pixels,
while the other field is read out at short intervals and the data used for guiding the
telescope. Half way through the exposure, we can read out the contents of the
integrating field, swap fields, and integrate the rest of the exposure on the other field.
This preserves the best image resolution and eliminates ‘aliasing’ effects.
To give a fast guider update rate, the guiding field is read out as an 80x40 window
around the guide object, while the unused lines are ‘dumped’. Using this technique, it
is possible to feed corrections to the telescope drive as often as one every second
when guiding on a fairly bright star (typically about mag. 11). The sub-pixel guiding
accuracy of S.T.A.R. 2000 will give you tightly defined, round star images, however
long the exposure time that you use!