In article , Ken Hart
wrote:

My smartphone takes reasonably good pictures despite a smeary slightly
scratched protective lens window. (It's not actually the optical surface
of the lens).

I used to caregully clean my 35mm Nikon SLR lenses every time I took the
camera out.

What is it about the optics on a smartphone which allows it to get away
despite such neglect?

Perhaps it's to do with something like the focal length or depth of focus?

Simple, the image focal point is nowhere near the scratched area so it
behaves more or less like a very mild diffusion filter at worst.

no.

actually, yes.

actually no.

a scratch on a tiny lens would be much more than a 'mild diffusion
filter', and it's actually *very* difficult to scratch the lens because
it has a protective cover (usually sapphire crystal), which does not
scratch easily, even if one tries.