One of the, we can perhaps call it this way, standard challenges any amateur astronomer faces is photographing a lunar mosaic. In other words: taking a sequence of large resolution images of different areas of the Moon, to assemble it later, and thus gain a large landscape but with the added extra resolution. Pretty straight forward. And everybody who’s ever attempted such an endeavor is familiar with stuff going south, picture below.
With that said, there probably are both software and software+hardware solutions out there. Honestly, I don’t care: I enjoy inventing these things, creating them, programming them, failing and overcoming the failures. So here’s what I came up with.
The above image shows the following:
- my astrophoto planner — won’t really be needed in the future. The photo planner is meant for deep sky photography, but it is the right UI to play with math that’s already there. And trust me, that math is not an easy one. The Moon is superimposed onto Aladin Lite’s Digitized Sky Survey viewer, with the right size, considered 1/2 deg across. I put it into Virgo, because it’s a nice empty space there.
- the large grey rectangle shows the field of view of an ASI 178MM camera on a guider scope of 200 mm focal length. Fairly typical, if not the focal length, the field of view most definitely.
- The white rectangle in the middle of the image is the field of view of an ASI 178MM camera through an instrument of 2700mm focal length, as shown on the right panel. This would translate to a fairly stendard 180/2700 maksutov scope.
- the green-yellow alternating rectangles are the same fields of view as above, projected to cover the Moon, while overlapping each other, as the UI indicates, by 1/4 on each side.
- as this is an „automatically go for” full lunar disk rendering, with the selected instruments, the software calculated that 5×7 frames are needed to safely cover the Moon.
The ideal setup, at least for me, would be as follows:
- Laptop 1, main instrument (white field of view), recording, manually for now.
- Laptop 2, guider scope. This laptop is running my soapbox autoguider with the requested parameters: detect the moon’s size in the field of view, and create the requested offset from the middle (center of gravity, if the moon is over exposed to be a white disk) corresponding to the matrix shown above.
- A precise enough mount to be guided. A HEQ5 would do for most intents and purposes, but the EQ3 I converted to be driven through ST4 commands, wasn’t precise enough even when still new.
- Clear skies…
- Align the views of the main instrument and the guiding instrument, aka Laptop 1 and Laptop 2
- On Laptop 2, make the calculations and detections (TODO: implement in the soapbox driving application),
- On Laptop 2, select the piece of the mosaic to record. The soapbox autoguider should apply the needed offset and get the desired field of view into the main instrument
- On Laptop1, when in position and being guided, record the video
- Keep repeating 3 and 4
Below, the soapbox autoguider following Saturn, imaged through a Methane filter. Printscreen: the autoguider steals the screen from Sharpcap and looks at the histogram for optimal results. TODO: implement the lunar disk size detection, the piece-generation as shown above, the piece-selection and… enjoy I guess. We’ll see when I’ll do it.