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A concave lens would disperse the rays. There would be no physical picture generated that you could capture with a sensor.

A silly question in retrospect :)

Dont worry. I dont judge.

There is specific type of weird and simple camera lenses with the principle of work like the telescope (concave mirror) like this one. Concave lenses are present in the most compound lens like this example since the late XIX century, but I don't know the example of a sole concave (conv + conc = telephoto)

It can be used with other types of lenses like your link but I dont think it is possible for solo use because it does not form a picture.

Are you sure there is not a concave mirror inside... Telescopes use reflex mirrors not lenses.

For the "telescope-like" camera lens, we got lost in translation (lens as objectif and lens as the optical lens), yes, the mirror is at the back.

One and only concave wouldn't make sense, you're right.
But, if you take a good lawyer... Fresnel lens could be some sort of concave :)

Hahahahha you are correct. :)