Starlight Xpress SXV-M25C - Manual (Page 23)

Handbook for the SXV-M25C Issue 1 June 2004
23
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.
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 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 tenth of 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 colour 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 the highlights. Aligning the images is always something of a problem, as
there are rarely any stars to use when imaging the planets, but Jupiter’s satellites can
be useful reference points. Otherwise, you will have to find a well-defined feature on
the planet, or estimate where the centre of the disk is located. Some more
sophisticated software can automatically align planetary images and you may find
these programs to be very useful (e.g. Registax’).
*********************************************************************
Using the add-on autoguider: