I've got to caution again that capturing full disk lunar or solar images using the HD video output of a DSLR isn't going to produce very impressive images. That video is going to be resampled and compressed before it is even output from the camera and in any case a one mega pixel image of the full disk of the sun or moon isn't going to provide much detail. That said, if you are only after low resolution images of the full disk then you might be satisfied with the results, so some of this will certainly be up to the eye of the beholder.
It is, however, possible to do some pretty good full-disk lunar and solar imaging using STILL capture with an APS-C camera. At low ISO settings you can even get nice images with a single frame and by stacking just a few still frames you can get even higher resolution and less noise.
Here are links to two images (one of the gibbous moon and the other of a solar eclipse) that I did with APS-C cameras using STILL captures:
Gibbous moon (On CN with a link to a higher resolution on Flickr, 5" refractor): https://www.cloudyni...-4#entry6719422
Solar eclipse (on Flickr, 80mm refractor): https://flic.kr/p/pv8pBA
Yeah, been running numbers, and it would be much less impressive for the 2019 Mercury transit than it will be for the 2019 total Lunar eclipse. I got the following for the size of Mercury in a Canon APS-C sensor at 1920*1080:
2 px @ 360 mm
2 px @ 420 mm
3 px @ 700 mm
3 px @ 714 mm
3 px @ 720 mm (1623 km/px)
4 px @ 840 mm (1392 km/px)
Still think I made the right decision in canceling the 5SE. I was getting it more for the OTA than for the mount. I think I will be better off with a 2X Barlow on a small refractor for the 2019 total Lunar eclipse, but I still might want a longer focal length for the 2019 Mercury transit and planetary observing in general.
Doing continuous shooting and then time-lapsing the video would not improve resolution at all though. E.g. taking one photograph per second for 60 minutes can be time-lapsed at 60 FPS into 1 minute of video at a very high resolution of 6000*4000 pixels. But if I want to share that video online (or even if I want to share any still photographs online), it will have to be compressed down to 1920*1080 or smaller anyway, and I will lose all of the extra resolution. It would be faster and easier to just film at 1080p and then remove the extra frames if I wanted to time-lapse. If I want planets with their small angular diameters to be framed well without significant loss of resolution though, I really need to get a camera with a smaller sensor, or a camera that supports region-of-interest filming.
Regarding sampling for Canon APS-C, I got the following:
(minimum theoretical resolution at red, green, and violet wavelengths per aperture)
50 mm. 3.52" / 2.53" / 2.01"
60 mm. 2.94" / 2.11" / 1.68"
70 mm. 2.52" / 1.8" / 1.44"
72 mm. 2.45" / 1.75" / 1.4"
102 mm. 1.73" / 1.24" / 0.987"
(resolution per pixel per focal length)
360 mm: 6.65"/px > 3.52" (360/50, 360/60)
420 mm: 5.70"/px > 2.45" (420/72)
700 mm: 3.42"/px > 2.94" (700/60, 700/70)
714 mm: 3.36"/px > 1.73" (714/102)
720 mm: 3.33"/px > 2.94" (2X 360/60)
840 mm: 2.85"/px > 2.45" (2X 420/72)
It seems that the 1080p resolution is undersampled, even with a 2X Barlow, so that increasing the aperture would not appear to increase the resolution. Therefore, the best option seems to be to get the longest focal length to get as much of the disc into the field of view (within an acceptable margin).
I capped out my OTA search to effective focal lengths between 634 mm (margin of 0.5 Lunar diameters) and 854 mm (margin of 0.25 Lunar diameters), and also to only OTAs of less than 15 pounds in weight. That eliminates the Newtonian astrographs, and puts my two top choices as a 360/60 refractor or a 420/72 refractor for grab-and-go full-disc Solar/Lunar videos with a Canon APS-C. I already ordered the Meade Adventure Scope 60 (360/60 achromat) to use as a wide-field deep-sky OTA on the 5SE mount. So I can keep that as my grab-and-go for quick full-disc Solar/Lunar videos (such as ISS transits, Lunar eclipses, and Lunar occultations), and then focus on getting something with a longer focal length for planetary imaging.
Edited by Nicole Sharp, 01 December 2018 - 07:55 PM.