Handbook for the TRIUS PRO-825C Issue 1 September 2020
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Other features of the TRIUS PRO-825C hardware and software
‘Slew & Sum’ imaging:
The TRIUS PRO-825C 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:
N.B. Binning will destroy any colour data – do not use binning for images that you
want to convert to true colour!
Up to this point, I have assumed that the full resolution, imaging mode is being
used. This is fine for most purposes, 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 pixel image with 4 times the effective
sensitivity. Using 2x2 binning, you can considerably improve the sensitivity of the
TRIUS SX-825C without losing a great deal of resolving power, so you may like to use
this mode for many faint deep-sky objects. 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.
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
