After watching the clouds gather during the day, I wasn’t hopeful that I would get a chance to image that night. I checked Astrospheric and saw that it would clear off with below average transparency and average seeing starting in the 1 O’clock hour. I could also see the temperature and dew points converging well before then, so I expected dew. The G11/Meade were already set up. The only additional set up was to add the ASI90. I set an alarm for 0100, went to bed at 2030, but woke up on my own at 0045.
I got dressed and was at the scope by 0100. Temps were in the mid-50s, RH was 94%, and the air was completely still. There was some moisture on my table, but not too bad.
As I had planned, I powered up and checked that the dew heater was on first, leaving the front cover on the scope allowing some time for the glass to warm up before exposing it to the moist air.
On going outside, I found a very gibbous waxing Moon well past the meridian, and Jupiter was just past it. Mars was not yet out of the trees at this point.
I did not check polar alignment. I expected it to be somewhat off as the new blocks under the tripod were sure to have settled, and that turned out to be the case. A little more guiding input was required from me than last time, but it was not excessive.
Since I already had the ASI290 on the scope, I slewed to Jupiter first and found it right at the edge of the 40mm eyepiece fov. I adjusted the scope to put it where I thought it needed to be in order to be visible on the FC display, and it was there when I flipped the mirror. Also, I noted that the filter wheel connected on start up. I verified that it was moving by watching two dividers past between R and G, and then G and B. I could also hear the filter wheel motor as it turned.
I captures 10 RGB runs at 30s per filter. Exposure was around 4ms and gain about 380. I was getting about 90 FPS. Histogram was peaking at just under 90% on all filters. The yield was just under 3000 frames per filter. The data looked pretty good as it was coming in.
Mars was not quite over the trees yet, so I decided to shoot the Moon next. As I was about to change over to the ASI178MC, I noticed that Jupiter’s historgram had decreased to about 50%. I checked the front of the scope and found that I was completely dewed up. I also noticed that the table was much wetter. This was feeling pretty close to Farm dew.
Seeing that I would soon be losing the Moon behind the cottage, I decided to pass on that target and see if I could get the front glass dried so that I could shoot Mars. Toward that end, I decided put the front cover back on the scope to see if the dew would clear while working on this report.
After giving it an hour to dry off, I came back out to attempt Mars. It was well above the trees. Even though it was not yet close to the meridian, I could tell that it was going to pass at a very high elevation.
I found that the front glass of the scope had completely dried. I noticed that the table had dried somewhat as well. I had no issue acquiring Mars, and I was struck at how much worse the seeing had become. Astrospheric was still showing below average transparency and average seeing.
For Mars, I shot 10 iRGB runs at 45s per filter. The exposure was about 4ms with the gain at 400. I was getting close to 450 fps with the histogram peaking at about 70% on all filters. The yield was about 20,000 frames per filter, which I hope will help compensate for the bad seeing. I did not feel very good about the quality of the data as it was coming in.
With the seeing being so bad, which makes precise focusing very difficult, I decided to try focusing on a star. I understand that mirror shift can change the focus when slewing from the star back to the target, but my thinking at the moment is that the resulting focus when I get back to the target is much better than I could achieve trying to focus on the target itself.
For this exercise, I first achieved the best focus (a guess) that I could on Mars itself. I then selected the star icon (instead of the Mars icon) and set the exposure to about 4s. I moved off of Mars and nudged the scope around until I found a star. It was not very bright, so I did not get sufficient diffraction spikes when I put the Bahtinov mask in front of the scope. I then tried slewing to Aldebaran, about 20 degrees away from Mars, and could clearly see the diffraction spikes. It turns out that my focus was off just a little from my best guess while trying to focus on Mars. I have decided to continue to use this technique for lunar and planetary imaging into the future.
The session ended at 0400.
In spite of the mis-cues that will be described next, the dew, and the seeing, I felt that this was a worth while session. I got some mistakes out of the way, gained some experience, and improved my technique so that I am better prepared for that perfect night should it ever come along.
The seeing and transparency were worse than expected.
First mistake tonight is that I did not do any planning. I should have opened Stellarium to see what features would be on visible on the three targets and to see where they would be placed. Not a horrible mistake, but that kind of situational awareness would have influenced the order in which I went after the targets. Second rookie mistake is that seeing what the dew situation was going to be, I should have put the dew shield/heater on the scope, and I should have allowed half an hour for it to heat up before removing the front cover. Third rookie mistake is that I am not feeling too good about collimation, so I should have set up the artificial star and checked it when I was prepping the scope yesterday afternoon.
I had no equipment issues. Everything worked as it was supposed to.