I am using Nikon D750 and I want to use it to record videos of planets/moon, so that I can later stack them into images. However, the camera wastes its potential by down-sampling the video recording to 1080p. So I wonder if there are (preferably affordable) ways that allow me to record video at 1:1 resolution or capture the zoomed live view signal.
HDMI recorder sounds like an option, though I lack experience in those and, as far as I can tell, a decent one is quite costly. ImagePlus seems like the answer, but a demo is available only via inquiry so I am not sure if it is what I need. Plus, I am certainly interest in knowing if there are cheaper, even free, options.