Handbook for the TRIUS SX-825 Issue 1 January 2015
12
exposure. If you take at least 10 such frames and average them together, the resulting ‘master bias’ can
be used to clean up readout defects for many months before CCD ageing changes require another set to
be recorded.
‘Flat fields’ are often recommended for optimising the results from your CCD camera, but these are
generally less important than dark frames, especially if you make sure that the optical window of the
camera is kept dust-free. The purpose of a flat field is to compensate for uneven illumination and
sensitivity of the CCD and it is better to avoid the need for one by keeping the optics clean and
unvignetted. I will ignore flat fielding for current purposes and describe the process in detail at a later
stage.
Processing a deep-sky image:
1) Make sure the ‘Auto Contrast Stretch’ is switched off and load your image into SXV_hmf_usb. If
you intend to subtract a dark frame, select ‘Merge’ and then ‘Subtract Dark Frame’. Pick the
appropriate dark frame and the software will then remove the dark signal from your image, leaving it
somewhat darker and slightly smoother than before.
M42 – 30 seconds exposure at F2 with a C8 Hyperstar
2) Once you have subtracted any dark frame, you can convert the raw image to colour.
