Regarding reading number plates at 5 miles.
This type of observation was easy with my 120mm refractor, but at 3 a.m. on good nights.
A clock tower clock about 5 ft diameter. But the clock was lit from behind.
The minute ticks were maybe an inch wide and 2 inches high or smaller.
My 6 inch Maksutov might have also done this on really steady days in September, but not in England.
Islands 5 mile distance were amazingly clear. There seemed to be no haze reduction at all at sea level. The air in Britain is too polluted for this.
The 70 inch aperture Big eye satellites were able to resolve better than 4 inches at 200 to 250 miles. Maybe using adaptive optics.
A 6 inch Maksutov type optics could lock on the specular reflection from a car door handle at 90 miles so I was told by someone involved with this type of optics.
Aircraft at 80,000 ft can photograph golf balls on the ground.
P.S.
The magnification on the 120mm f/8.3 refractor was 250x. 330x was tried but no gain.
The 6 inch Maksutov was used at 95x, but I would need to increase this to 150x or 200x.
I have read a hotel name sign at 11 miles with a Japan Celestron 20x80 but cannot remember how large the letters were.
With car number plate letters some are difficult, some easy, depending on crowding.
The light levels are critical for long distance viewing
P.P.S.
Horace Dall showed me photos he took with his 110mm aperture f/30 camera obscura objective corrected for 4 colours.
Some were of church gutters 17 miles away, which were clearly visible with detail.
Also photos of Mercury with an equivalent focal length of 1,100 metres taken with his 16 inch Dall Kirkham. He used his atmospheric dispersion corrector, which I think he invented.
Seeing the daytime scene in his darkened attic on the large round white table presented by his camera obscura in beautiful colour was an experience like no other. There was a table microscope to show very fine detail.
The views of the planet Mars at 400x with his own made 8 inch Maksutov through his specially selected and ground attic plate glass window, was another experience that had to be seen to be believed.
I think that an 80mm Pentax spotting scope may be a little small to read number plates at 5 miles.
Someone I think described seeing 0.22 inch holes at 1 mile with a 100 Pentax spotting scope.