From Erwin Rene van der VELDEN
® . . . . . . . .Sent:
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.
Cheers,
® . . . . . . . Sent:
Subject: Mars 2003/7/14
Animation
Hi,
I couldn't resist to
make an animation as well. This shows the fading of the bright spot a
bit better.
Cheers,
® . . . . . . . .Sent:
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
Thanks for sending all your images, I put them in separate folders for comparison.
Cheers,
® . . . . . . . .Sent:
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.
Cheers,
Erwin van der VELDEN (Brisbane, Australia)
ErwinvanderVelden@compuserve.com
