system
Given the following post, respond as if you're commenting on Reddit:
human
How small and detailed could we make a Fresnel lens?

Seeing them in the wild, you either look at it from a distance or they're quite grainy, I know they're cheap.

So, probably the image might look slightly like the way insect-vision is portrayed in movies, segmented like, but if we can make the tiny tiny little mirrors and sensors in DLP projectors and smartphone camera sensors, (I don't know if the features are smaller on phone cams or pro 16k cams or what) is there any way, expensive and convoluted it may be, to manufacture a super small scale fresnel lens that would provide a clear picture.

I understand this would likely never be profitable in a smartphone or anything but I just love the idea of a telescope that's much wider than it is long, or a pair of binoculars that's scarcely thicker than some thick glasses.

In case you can't tell I don't know how optics work.. I flaired it for Engineers because I suppose that's closest? Rather than physics?

I also just imagined a microtelescope could be made using a DLP mirror module as the collecting mirror with a little sensor in front of it, the uses however, escape me, aside from proof of concept or just messing about.
gpt
In an ordinary Fresnel lens, the step changes in thickness are not especially damaging to their performance; you can mostly ignore them. But as the steps get closer together, they start to really matter. You end up in a regime where the device would be considered a diffractive optical element (DOE).

The steps should have a height that depends on the wavelength, and on the angle of incidence. A "blazed grating" is an example of a diffractive element that has a simple sawtooth pattern. The main use of such a device is to disperse different wavelengths into different directions, and to do so with a high efficiency into one direction in particular.

DOEs are very useful devices, and they can be cheaply manufactured. You heat up a soft material, and you press a hard stamp into it - that's a form of nanoimprint lithography (NIL). It's not out of the question to find a DOE in a consumer product. (For example, many credit cards have a plastic hologram.)

Unfortunately there is a catch to making a diffractive lens: the exact shape of the DOE has to be tuned to the wavelength of interest. A DOE that efficiently focusses one wavelength to a tiny point, will be unlikely to focus another wavelength to the same point. So that's a challenge to using them in a colour camera.