Another imaging session under very good seeing conditions. The subject: once again, our Moon.
With the 14inch telescope I had again the pleasure to get some sharp images of lunar features under some similar seeing conditions as for the previous HR (High Resolution) posts (1, 2, 3). Despite this, I had to deal with the dew accumulating on the secondary mirror of my open-tube design telescope. At the end of the post it will become apparent why this happens.
The images were acquired with the following equipment: 14inch (355mm) F/5 homemade Newtonian (SkyWatcher optics) working at F/20 and F/25 using a Baader Hyperion Barlow lens (2.25x, and expanded to 4x and 5x using different adaptors), the ASI 120MM-S camera and a Baader Red filter.
And now, the images.
Tycho (lower right) with Clavius (top):
Rima Triesneker with crater Triesneker (center, with the caldera in darkness) and the double crater Murchinson/Pallas (to the right of Triesneker). Lots of interesting details are visible due to the low-Sun illumination:
A large mosaic (six frames) presenting a well known trio of craters (Arzachel, Alphonsus and Ptolemaeus, from top to just below of center) and the less imaged large craters Albategnius (in shadows with the central peak just illuminated) and Hipparchus (below Albategnius) on the lunar terminator:
Albategnius shows some very interesting details on its floor under this illumination, with the rims of small craters well defined, and also some depressions well defined:
Some color data (from here) was added to the above six-frame mosaic, and the resulting image shows even more details due to this, like the yellow area surrounding two small craters (to the right of Arzachel, top right) named Lassell G and K. This is an old volcanic area.
Plato was imaged last in this session. Due to the good seeing conditions, a lot of small craters are detectable onto its floor, as is the rima just to the lower-left of Plato, on the mare floor.
To better see the smallest detectable craters (around 600 meters in diameter) I’ve highly re-processed the above image:
Comparing the above image with a view from LRO (right), to match the craters in my image (left) with what is really there:
And since I usually try to get more from my images, a “rectified vertical perspective” view of some craters performed in order to grasp the true shape of these craters. From left to right: Tycho, Plato and Clavius:
I was writing at the beginning of this post about the dew accumulation on the secondary mirror of the 14 inch telescope. Well, for now I cannot solve this problem in an elegant way, but the solution will be implemented soon.
The reason for the problem will become apparent from the image below, shot by my wife during a solar imaging session. The mirror-like disc at the front end of the scope is the Mylar solar filter. This is of course removed during night-time imaging 🙂
This is the way a 14 inch Newtonian should look 🙂 (or not…). Despite not being the most handsome scope around, it does perform very well, and the cool-down time during lunar imaging sessions is around 40 to 70 minutes (depending on the initial temperature of course). Besides this, the total weight of the scope is around 18 kilograms, which is the maximum an EQ-6 mount can handle for planetary guiding. The scope itself is still under construction, with a lot of parts being redesigned after the imaging sessions, but the general shape is final.
Hope to finish the work by the end of the year…