On the night of the 19th of November 2005
I was blessed with some exceptional seeing. With Mars so unusually
steady in the eyepeice I took the opportunity to image the planet
using various image scales. To do this I used a Celestron APO Barlow
lens and various extention tubes I had to hand. I also used my Mogg
0.6 focal reducer to complete the test. I was interested in the
actual magnification effect over Newtonian focus of the Barlow and
various extention tubes and also the usefulness of that extra magnification
in obtaining a better image. |
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For this test I took an image of Mars during some very good seeing. The following table shows some of the parameters of the test...
*Resolving power calculated by the formula: |
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The images above are the processed results if the various tests. All were 3600 frame avi's and all were processed to bring out the best result. Images 1 to 4 were processed essentially the same
way: Registax3 Wavelett 1 at 100%, Gausian Blur - Unsharp Mask -
Gausian Blur in Serif PhotoPlus 8. To obtain the size of each Mars image I cropped the image to only contain the planet itself, with no gap at the top, bottom or sides, and took an average of the height and the width measurement of the resulting image. |
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From a comparison of the images I would
suggest that Image 2 or image 3 show the most detail. The sampling
rate for these images is 4x or 3x the resolution of the telescope,
respectively. The accepted minimum good sampling rate to avoid loosing
data is 2x the image resolution of the telescope. This test suggests
that sampling at a minimum of 3x the telescopes resolution (i.e.
at about F30), at least
in good seeing conditions, will give better results. Below are all the images again, this time with
all shown the same size. When shown this way image number 3 appears
to show the most detail. |
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