Starlight Xpress SXVR-M26C - Manual (Page 19)

Handbook for the SXVR-M26C Issue 1 March 2010
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time, the image noise level will be increased, and if too long a time is used you will
saturate the highlights and cause white patches on the image. With the recommended
focal length, Jupiter and Mars will both need an exposure time of between 0.1 and 1
seconds and Saturn will need between 0.5 and 2 seconds.
Processing a planetary image:
Planetary images have one major advantage over deep sky images, when you come to
process them – they are MUCH brighter, with a correspondingly better signal to noise
ratio. This means that aggressive sharpening filters may be used without making the
result look very noisy and so some of the effects of poor seeing can be neutralised.
A raw image
Try applying an ‘Unsharp Mask’ filter with a radius of 5 and a power of 5. This will
greatly increase the visibility of any detail on the planet, but the optimum radius and
power will have to be determined by experiment.
Jupiter after the application of an ‘Unsharp mask’
In general terms, the larger the image and the worse the seeing, then the wider the
radius for best results. My Jupiter shots are usually about one third the height of the
CCD frame and I find that the ‘radius 5, power 5’ values are good for most average
seeing conditions. If you have exceptionally good conditions, then a reduction to R=3,
P=3 will probably give a more natural look to the image, as too large a radius and
power tends to outline edges with dark or bright borders.
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