Last night, I used the 16-inch telescope to take pictures of Mars, which will reach its greatest apparent size in a week or so.
I opened the roof, turned on the equipment, and set up the CCD camera at Cass focus. At about 10:23 PM, I started taking test pictures, but the Pictor CCD control program crashed soon thereafter. Rats. I restarted and tried again. It took me a long time -- from 10:36 to 11:00 PM -- to focus on Spica. I finally selected a setting of T = -26,750 as the best focus position with no filter.
An exposure time of about 5 msec is about right for Mars with no filter.
I took a set of 11 pictures with analog binning on, which is the usual mode. This bins 2x2 on the chip, yielding an image of 384x256 pixels. I also took a set of 10 images without the binning. The images are larger (768x512), but I think this is a better arrangement for tiny Mars. The planet's disk has a diameter of about 50 pixels without binning.
The pictures with no filter show a bit of detail, but not much. The north polar hood and Elysium are barely visible.
I then put the Wratten number 25 red filter on the CCD camera and re-focused. The best value, T = -26,730, was about the same as without a filter. Convenient. I increased the exposure time to 10 msec; it would be okay to go to 15 msec, too.
I took a set of 10 images binned, and another set of 10 images unbinned, through the red filter. The unbinned images look better. Here's an example of the appearance of one image in raw form (as it comes from the camera), and after a little processing with Photoshop with an unsharp mask:
I used unsharp mask parameters
Here are the best 5 images, all taken with the red filter and unbinned: all were taken in quick succession at about 11:55 PM EDT, which is 27 Apr 3:55 UT.
For comparison, here's a big map of Martian features at that time; note the orientation. I've flipped it to match our pictures, but it's still about 30 degrees off. The northern polar cap is surrounded by a dark hood, which appears in our images. One can also see the dark feature called "Elysium" just below the northern polar hood in our pictures, and a hint of the "Alcyonius Nodus" coming around the western limb. Syrtis Major would appear about 4 hours later.
For a fair comparison, here's the same chart, reduced in size, in both color and greyscale, together with one of our images.
