R5 lunar photography with stacked EF extenders

Tristimulus wrote:

Bigger wrote:

Sure, aperture diameter is everything. But what about a 6" scope, other than price, would make it better than a 6" lens, e.g., 600mm f/4 for lunar photography?

Telescopes have diffraction limited resolution (and are usually used at f/20 - f/40 for high resolution solar, lunar and planetrary images). For infinity focus only.

Telephoto lenses do not have diffraction limited optics (residual abberatins are larger than the airy disk). But they are well corrected for a wide focus range, from near to far.

So different kinds of optics for different jobs. Both are optimized for the job at hand.

Aside from optimization for infinity focus, according to this formula, Nyquist limited sampling with a 600/4's 150mm aperture & an R5's 4.38um pixels would be minimum f/16, but oversampling by 2x is common, so f/32, which checks with your recommendation above. We could get a 600/4 up to f/16 with two 2x stacked converters, but as you say, that's probably pushing the limit of diminishing returns, so oversampling at the pixel level is not reasonably feasible with a photo camera & lens. That could be compensated somewhat by oversampling at the image level, i.e. just stacking more images, e.g., shooting 8k video as in the example here.