LtE in CMO #275

FromErwin Rene van der VELDEN

. . . . . . . .Sent: Thursday, July 17, 2003 1:50 PM

Subject: Mars 2003/7/14



Dear Masami,


already a few nights ago I took a sequence of Mars and noticed afterwards a bright spot next right to Syrtis Major that faded away within one hour. Does anyone know what the cause might be (besides a very coincidental bright artifact on two separate stacked images).


In the days beforehand I tried to reduce the spherical aberration and astigmatism by rotating and shifting the corrector plate of my C8, a very tedious task giving the limited testing equipment I have. By rotating the plate with 10 degrees and 0.3 mm shift I reduced the spherical aberration from 0.50 to 0.20 and the astigmatism from 0.25 to 0.10 wavelength, which translates into a higher contrast and an increased number of usable frames because of less sensitivity to seeing variations. Don't ask me why it was so far off!


There is still an issue with the smearing of the CCD camera, that is especially visible near the terminator, I'll try to counter it by rotating the camera 90 degrees to put the terminator in a horizontal direction, maybe this will give an improvement.




. . . . . . . Sent: Thursday, July 17, 2003 1:49 PM

Subject: Mars 2003/7/14 Animation




I couldn't resist to make an animation as well. This shows the fading of the bright spot a bit better.




. . . . . . . .Sent: Saturday, July 19, 2003 3:27 PM

Subject: Mars 2003/7/17


Dear Masami,


Yesterday was another opportunity to make some piccies. As promised before I managed to almost get rid of the terminator artifacts by putting the terminator on top, I also changed the exposure times back again from 1/33 to 1/25 s. Seeing was average for the 16:36 image and a bit better for the 17:08 image. I also simplified the processing to reduce artifacts, it's now 1 wavelet, 1 gamma and 1 colour correction. I think the 17:08 is the best. Tomorrow another try?


Thanks for sending all your images, I put them in separate folders for comparison.




. . . . . . . .Sent: Wednesday, July 23, 2003 12:24 PM

Subject: Mars 2003/7/21



Hi everyone,


Here another Mars observation under a 2/10 seeing and a partly cloudy sky. With the C8 in the old state any attempt to make an image was useless, but to my surprise the image that rolled out of my PC still looks decent, although the very small details are a bit washed out.





Erwin van der VELDEN (Brisbane, Australia)

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