With Mars the having its last closest approach for some years, I decided to start testing my new 16" telescope. The weather in San Diego has been uncharacteristically cloudy in October, so my first opportunity was at the end of the month, near closest approach. With pretty good seeing, it turns out that the optics have some astigmatism that limits the resolution, but fixing that will have to wait. Realistically, seeing and atmospheric turbulence will limit most imaging. Even though the planet does appear pretty high in the sky in San Diego, correcting dispersion is still required, and is done by shifting the red and blue frames by less than a pixel.
October 28, 2005, 10:35 pm PDT, 1000 frames captured, best 500 summed, 4 msec exposures. Click on the image to bring up an avi file of the first 50 frames with no processing (except cropping). 2.5x Powermate, effective focal length 5.0 meters, equivalent F/12.5, Mars 20.16 arcsec diameter, 49 degrees altitude, seeing 6/10. Very clear skies, but high humidity - everything was covered with dew. Mirrors within 1 deg F of air temperature, small fans continuously operating, large fan off. Lucy-Richardson deconvolution processing followed by unsharp masking.
Mars had a satisfying amount of contrast on the monitor, making focus relatively easy. North is up in the image, and a weak blue polar hood is visible. No southern polar cap is seen. Other imagers have noted some dust storm activity in the last few weeks, but it is not yet global, so nice images are still possible. Note that the IR blocking filter was inadvertently omitted for this and the next few series. This means that the IR radiation leaks strongly into the blue pixels, so the focus will be worse and the colors distorted.
The first tests this summer with the 16" telescope. Earlier in the evening, I fine-tuned the finder scopes and the collimation. The seeing was very good early in the evening - the out-of-focus diffraction rings were nearly stationary. This good seeing allowed me to confirm what I suspected from earlier tests - the system has some astigmatism, preventing good focus. The JMI DRO motofocus indicates a difference of about 0.1 between the two focal points. The resolution is probably about the same as would be provided by a 10" aperture. The axis is aligned with the RA and DEC, but the mirror mounts all use three-point mounting symmetry. I will try to bend the mirror, or add a weak cylinder lens to see if I can correct the image.
October 29, 2005, 8:35 pm PDT, 9:49 pm PDT, and 11:08 pm PDT (left-right). 1000 frames captured, best ~350 summed, 4 msec exposures. Click on the center image to bring up an avi file of the first 50 frames of that image, with no processing (except cropping). 2.5x Powermate, effective focal length 5.0 meters, equivalent F/12.5, Mars 20.16 arcsec diameter, 25 degrees, 41 degrees, and 57 degrees altitude, respectively, seeing 5/10. Very clear skies, but high humidity - everything was again covered with dew. Mirrors within 2 deg F of air temperature for the first two images, then within 1/2 degree for the last image. Small fans continuously operating, large fan off. Only unsharp masking applied. Not much different from the previous evening; maybe the dust storm on the far left side is a bit smaller. No IR filter.
November 4, 2005, 9:34 pm PST. 1000 frames captured, best 65 summed, 4 msec exposures. Click on the image to bring up an avi file of the first 50 frames of that image, with no processing (except cropping). 2.5x Powermate, effective focal length 5.0 meters, equivalent F/12.5, Mars 20.03 arcsec diameter, 56 degrees altitude, seeing 4/10. Very clear skies, but high humidity - everything was again covered with dew. Mirrors within 1 deg F of air temperature. Small fans continuously operating, large fan off. Only unsharp masking. Since the seeing was so poor (see the .avi file), only the best 65 frames were combined, using both quality and difference discriminators in K3CCDtools. The noise was still acceptable if at least this many frames are added. Note that the color frames were shifted to compensate for atmospheric dispersion, so the blue North polar hood is even more distinct. No IR filter.
November 5, 2005, 9:14 pm PST (left) and 11:16 pm PST (right). 1000 frames captured, best ~100 summed, 4 msec exposures. Click on either image to bring up an avi file of the first 50 frames of that image, with no processing (except cropping). 2.5x Powermate, effective focal length 5.0 meters, equivalent F/12.5, Mars 19.98 arcsec diameter, 53 degrees and 73 degrees altitude, respectively, seeing 6/10. Clear skies, but high humidity - everything was again covered with dew. Mirrors within 1 deg F of air temperature for the first image, then within 1/2 degree for the second image. Small fans continuously operating, large fan off. Only unsharp masking applied. Not much different from the previous evening; but better seeing. No IR filter.
Mars January 10, 2006
January 10, 2006, 7:30 pm PST (left) and 8:57 pm PST (right). Left image: 1000 frames captured, best ~120 summed, 10 msec exposures. Right image: 2000 frames captured, best ~120 summed, 4 msec exposures, higher gain. Click on either image to bring up an avi file of the first 50 frames of that image, with no processing (except cropping). 2.5x Powermate, effective focal length 5.0 meters, equivalent F/12.5, Mars 10.8 arcsec diameter, 74 degrees and 62 degrees altitude, respectively, seeing 6/10. IR filter installed.
Clear skies, but moderate humidity from weak offshore winds. Primary mirror only within 5 deg F (left) and 3 deg F (right), due to rapidly falling air temperature. Small fans continuously operating, large fan off. Only unsharp masking applied. Mars is starting to hover over the neighbor's house, so the local seeing is worse for this reason after about 8 pm.
Mars is pretty small, but this was the only opportunity since last November, and might be the last of the season. The astigmatism of the primary mirror was apparent when focusing. The spring on the back side had broken off in the last windy storm, so it the mirror could not be adjusted. If there is anoher good seeing night, I'll have the mirror adjuster fixed by then, and hope to get good images, even with Mars even smaller.
Mars January 21, 2006
January 21, 2006, 8:32 pm PST. 2000 frames captured, best ~100 summed, 10 msec exposures. Click on the image to bring up an avi file of the first 50 frames of that image, with no processing (except cropping). 2.5x Powermate, effective focal length 5.0 meters, equivalent F/12.5, Mars 9.7 arcsec diameter, seeing 5/10. IR filter installed.
Clear skies, low humidity from weak offshore winds. Primary mirror within 2.5 deg F, due to rapidly falling air temperature. Small fans continuously operating, large fan off. Only unsharp masking applied. Mars is starting to hover over the neighbor's house, so the local seeing is worse for this reason after about 8 pm. Experimented with different astigmatism (bending the mirror), and had too much for the earlier shots when the seeing was better. Still need to try different arrangement (change by 90 degrees, motorize. )
Mars is pretty small, and this might be the last opportunity this season. The astigmatism of the primary mirror was apparent when focusing. The spring on the back side was repaired, and it was adjusted by looking in the eyepiece at a star. While the springs appeared to help, the in-out image tests still show a lot of astigmatism.
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