The Backyard Astronomy class has been over for more than a week now and imaging with the long focal length14" is taxing. Time to rehang the 102mm f/7 Explore Scientific triplet. New mounting rings have been fabricated and installed. Tonight the scope was mounted and aligned.
This evening's objective is to determine the optimum setup for capturing the eclipse. AVI files are huge to start with. Since I’ll be running multiple AVIs to capture the eclipse sequence and since seeing is normally the limiting factor with resolution, can I get away with binning?
Finished setup/alignment/adjustments around 20:00. The moon will be full in 28 hours. Running the 6200 X 4200 full frame size results in a frame rate of only 3 or 4 fps. Cropping to 3600 x 3600 frame size doubled the capture rate.
All images are processed thru AutoStakkert, Registax 6 and PhotoShop.
Unbinned, 10% of 1000 frames, 120 gain, 1/250 sec exposures, -10C
- Luna 1X 4ms 120g -10c.jpg (1.22 MiB) Viewed 317 times
Binned 2X 10% of 1000 frames, 120 gain, 1/1000 sec exposures, -10C
- Luna 2x 100fo1000frames 120g 1ms -10c redo.jpg (323.76 KiB) Viewed 317 times
Unbinned 1/250 sec exposure close up
- Luna 1X 4ms 120g -10c closeup.jpg (1.07 MiB) Viewed 317 times
2X binned 1/1000 sec exposure close up
- Luna 2x 100 of 1000 frames 120g 1ms -10c redo closeup.jpg (655.24 KiB) Viewed 317 times
Conclusions & lessons learned:
Both unbinned and 2X binned AVIs took about 8 minutes to capture, although the 2X binned file size is much smaller and faster to process. I’d hoped for higher capture rates as 5000 frame AVIs would be better. So while smaller frame size does speed up capture rate binning does not.
Even with the tracking changed over from sidereal to Luna the frames tended to slowly drift to the NW, so every 30 seconds or so I’d tweak things using manual guiding adjustments. Used crosshairs to nail position and the scope’s very lowest “guide rate” speed.
I’d anticipated that I’d lose no resolution by binning and that binned frames would benefit from the shorter exposures. But that was not the case. The uncropped comparison images are pretty much the same but with enlargement it’s obvious that I was wrong.
The amount of sky one pixel sees = 206 X (pixel size in microns) / (scope focal length in mm)
So my setup's unbinned coverage calculates to be 1.33 arc seconds per pixel, vs. 2.66 arc seconds binned 2X. Local seeing is usually 3 or 4 arc seconds so theoretically 2X should be fine. But it appears that high speed exposures can capture some frames with seeing better than 2.66”
I’m logging this work on Monday Nov 7, and given wind and given my high western horizon looks like I’ll be given tonight’s eclipse a pass. But this activity was certainly educational and of future benefit.
