The dimmest that can be achieved from Earth telescopes is around magnitude 28, with as I recall the original Dragonfly team going 40 times fainter and being able to image magnitude 32 with a 48 lens array. This compared with a human eye visual limit of perhaps 6 or 7.
All the usual stuff required: Low noise, high signal to noise ratio, low optical aberrations, low scattering, long exposure, large aperture, dark sky, good tracking, good processing.....
Best
JA
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