Starlight Xpress SXV-H9C - Manual (Page 26)

Handbook for the SXV-H9 Issue 1 June 2002
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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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Other features of the SXV-H9C hardware and software
‘Slew & Sum’ imaging:
The SXV-H9C can be used in an automatic image-stacking mode, called ‘Slew &
Sum’. The camera is set to take several sequential exposures, which are automatically
‘slewed’ into alignment and then summed together by the software. This mode can
help to overcome a poor RA drive by summing images that have exposure times
shorter than the drive error period. The resulting image has more noise than a single
exposure of the same total length, but this method of imaging is still an effective way
of making long exposures without a guider.
To take an S&S image, go to the camera interface window and select an exposure
time for one image of the sequence. Do not use a very short exposure time, as the
read-out noise will become dominant. About 30 seconds is a reasonable minimum.
Now go to the ‘Multiple Exposure Options’ and select a number of exposures to take.
You can also select to average the images, rather than adding them, and there is a
‘Alternative Slew Mode’ available, which uses the correlation of image areas, rather
than a single star. This mode can be better in dense star fields.
Another option is ‘Auto remove dark frame’. This is advisable with S&S images, as
the slewing will mis-register the images with a single dark frame that is applied to the
finished sequence. To use this option, you will need a dark frame, taken with the same
exposure time as a single image from the sequence. This is stored on drive C with the
name ‘dark.def’
Now click on ‘Take Picture’ and the sequence will begin.
Using the ‘Binned’ modes:
Up to this point, I have assumed that the full resolution, imaging mode is being used.
This is essential for colour imaging, but it will often provide more resolution than the
optical system, or the seeing, allows. ‘Binned 2x2’ mode sums groups of 4 pixels into
one output pixel, thus creating a 696 x 520 pixel image with 4 times the effective
sensitivity. Using 2x2 binning, you can considerably improve the sensitivity of the
SXV-H9C without losing a great deal of resolving power, so you may like to use this
mode to capture many faint deep-sky objects in monochrome. Other binning modes
(3x3 and 4x4) are available and will further increase the image brightness and reduce
its resolution. However, generally, these are more useful for finding faint objects, than
for imaging, as the colour information is lost in all these modes.
Taking and using a flat field:
Flat fields are images, which display only the variations of illumination and
sensitivity of the CCD and are used to mathematically modify a wanted image in such