Arthur, thank you for your kind comments and encouragement.
For something like the first two images, using a standard lens and cropping could work, as they don't necessarily require the full resolution of the 24MP sensor, and one can shoot the scene either at lower ISO or faster shutter speed.
As for the last shot, however, I wanted to retain the patterns of the moon. It was shot at ISO12800 and f8.0, so I could have lowered the ISO to 3200 and shot at f4.0 for less grain and a bit wider dynamic range. But I'm not sure the detail of the moon could be captured with a 50/1.8 lens. (I used Ai 200/4.0 lens for all three shots and not cropped.)
Nevertheless, the experiment according to your suggestion is well worth trying. Thank you again!