[Wavytone]

Bratislav, you’re right in one respect - the resolution of camera lenses isn’t diffraction-limited - or does it need to be - there are a whole raft of conflicting imperatives which lead to a trade-off (ie a balanced compromise) in the lens design:

- wide aperture (ie f ratio under 4 and in some cases 0.95);
- minimal vignetting and distortion over the field of view, or else correct these in software;
- flat focal plane to match the sensor;
- reasonable image quality (MTF) over the whole frame out to the corners which means chromatic and monochromatic aberrations must be controlled in a balanced way.

Hence 10 or more elements are not unusual. The issues of focusing, zooming, weight and variable aperture have no bearing on the lens design.

A telescope design becomes far simpler fundamentally because the sheer cost of much larger aperture glass dictates fewer elements and the rest - including choice of focal ratio follows from that. Or switching to a mirror.

Perkins Elmer did for example produce a 5-element lens 20cm clear aperture f/5, though in current $ you wouldn’t have much change out of $1M, and it required a crane and truck to lift/move it.

The cost and difficulty in making optical blanks of sufficient perfection is what drives the cost of lenses 20cm and larger - take a look at the APM website to see what I mean - they are astronomical, literally.