Starlight Xpress SXVF-H16 User Manual
Page 14
Handbook for the SXVF-H16 Issue 1 August 2006
14
image. Strong ‘High Pass’ filters are usually not a good idea with deep sky images, as
the noise will be strongly increased and dark rings will appear around the stars, but a
‘Median’ filter can remove odd speckles and a mild ‘Unsharp Mask’ (Radius 3, Power
1) will sharpen without too much increase in noise.
Another thing to try is the summing several images for a better signal to noise ratio.
Summing can be done in the ‘Merge’ menu and involves loading the first (finished)
image, selecting a reference point (a star) then loading the second image and finding
the same star with the mouse. Once the reference is selected, you can either add
directly, or average the images together. Averaging is generally better, as you are less
likely to saturate the highlights of the picture. The signal-to-noise ratio will improve
at a rate proportional to the square root of the number of summations (summing 4
images will double the signal-to-noise), but different exposures must be used.
Summing an image with itself will not change the S/N ratio!
A deep image of the Deer-Lick galaxy group by Rick Krejci
Although I have concentrated on the use of a telescope for deep-sky imaging, do not
forget that you have the option of using an ordinary camera lens for impressive wide-
field shots! A good quality 200mm F3.5 lens with an infrared blocking filter will yield