Saturn with a Telephoto Lens (March 20, 2004)
Saturn with a 500 mm f/4 telephoto lens, plus 1.4x plus 2.0x teleconverters. Total focal length = 1400 mm, at f/11.2 (125 mm aperture). Exposure time was 1/20 second on a stationary camera tripod. Canon 10D digital camera. This image is an average of 99 frames registered and converted to 16-bit, then resized 2x larger, manually graded for image quality, and averaged with weighting according to image quality. Then the image detail was improved using Richardson-Lucy adaptive restoration: 10 iterations with a 9x9 box, then 70 iterations with a 7x7 box. Image processing was done in ImagesPlus 1.72, then final stretching (a small tweak) in Photoshup. See the below images to get an idea of the improvement achieved by this method. Plate scale on this image is 4x the original = 0.27 arc-second per pixel. Hints of the Cassini Division, a dark gap separating the outer slightly fainter "A" ring from the Brighter "B" ring is seen. The Cassini Division is about 0.8 arc-second wide. The diffraction disk diameter is 2.2 arc-second, and the Dawes limit (~0% MTF) is 1.1 arc-second. Thus, the adaptive restoration improved image resolution to a little better than the Dawes limit. The total improvement in spatial resolution is on the order of 3 times.
A single frame from the 99 frames averaged. This image was better than average.
The original weighted average image before image restoration.
Same weighted average image as above but image improvement using only Photoshop unsharp mask, two passes. Clearly the result is not as good.
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Last Updated March 19, 2005