Why are, generally, used different camera in rear and front cameras of a smartphone?

[luquinhas0021]

It's a technological limitation?
It's possible to do a smartphone with same camera system (Lenses and sensor), in rear and front sides?
It's possible to use flat lens, instead spherical or aspherical ones?

[Asmodian]

Pure price/performance and market driven. People don't care if the front camera is lower quality so they use a cheaper/smaller one.

Same with the lens type, the lenses used are those that the companies think people want, with price also a concern.

[hello_hello]

Does the front camera need to be as good as the rear one, given the front camera is primarily for taking selfies and uploading them to Facepage, or whatever it's called.

I must be old. I can remember when phones only had one camera. My Android smartphone probably doesn't have a front camera. I'd have to check to refresh my memory as I rarely take photos, but it's ancient for a smart phone (it must be 5 - 6 years old).

[Gser]

Size is the biggest factor. As you can see by looking at a phone with camera's on both sides the one in the front is minuscule in comparison to the back camera whose optics require that big bump on the outside. The bigger the optics the more light can enter the sensor, of course the sensor size is also larger at the back also. The front camera imo doesn't need to be as good as it is primarily for video calls and self-obsessed selfie taking narcissists.

[luquinhas0021]

Pure price/performance and market driven. People don't care if the front camera is lower quality so they use a cheaper/smaller one.

Same with the lens type, the lenses used are those that the companies think people want, with price also a concern.

I've never seen a camera with flat lens. I've seen only with aspherical and spherical ones.
Is it possible use flat lens, maintaining or increasing the photo quality in comparison with the use of aspherical lens?

[Asmodian]

I've never seen a camera with flat lens. I've seen only with aspherical and spherical ones.
Is it possible use flat lens, maintaining or increasing the photo quality in comparison with the use of aspherical lens?

Of course, if you could make them small enough and cheap enough, it is possible. Flat lenses aren't anything special as far as the sensor is concerned, but they would make an only slightly better camera. Chromatic adoration isn't too big of an issue in modern cell phone cameras, is it? It would allow new applications for optics but it isn't that big of an improvement for selfies. ;)

The reason you never see them in cell phones is that it was only this February that researchers at the Harvard School of Engineering first demonstrated a flat lens that worked from 490 nm to 550 nm (still missing red, and I want down to 450-460 nm too). The physics for wide spectrum flat lenses, and flat lenses in general, is still quite tricky. Certainly not in cell phones yet. First use of them may be military surveillance drones?

I am curious how long it will take to see them cheap, small, and stable enough for use in consumer goods. A VR headset with flat lenses would be much better than what we have now. :)

Though there might be easier ways to solve the current lens issues with VR. :p

[jmac698]

I thought that was a strange question, as a lens has to be curved to bend any light :) It's only recently that a concept of flat lens has been possible, as this requires a negative index of refraction, which is normally not possible. Now it's done with meta-materials, which means a certain pattern of pillars and rings (or other such patterns) is etched at very small scales, and this has the equivalent effect of -ve refraction and therefore you can make flat lens.

The problem in developing the technology is making the patterns small and precise enough as they have to be of the order of the wavelength of light. Also one pattern only really works for a small range of frequencies but I don't know exactly how they solve that (maybe a combo of patterns or some unique new approach to patterns).

If they could do that, I wouldn't even worry about cellphones - this technology would open up near field microscopes (seeing atoms with light), applications in fiber communications, amazing telescopes etc.

[luquinhas0021]

I thought that was a strange question, as a lens has to be curved to bend any light :) It's only recently that a concept of flat lens has been possible, as this requires a negative index of refraction, which is normally not possible. Now it's done with meta-materials, which means a certain pattern of pillars and rings (or other such patterns) is etched at very small scales, and this has the equivalent effect of -ve refraction and therefore you can make flat lens.

The problem in developing the technology is making the patterns small and precise enough as they have to be of the order of the wavelength of light. Also one pattern only really works for a small range of frequencies but I don't know exactly how they solve that (maybe a combo of patterns or some unique new approach to patterns).

If they could do that, I wouldn't even worry about cellphones - this technology would open up near field microscopes (seeing atoms with light), applications in fiber communications, amazing telescopes etc.

So a aspherical lens with almost zero curvature would be the solution?

[jmac698]

No, I believe it works like this with a flat lens. Forget thinking of a flat piece of glass. The curvature is controlled by varying the nano pattern in the material. It is truly flat over the entire surface. Something like:

* * * * * * *
* * * * * *
* * * * * * *

Which means, the density of the pillars is what changes the bending.
https://en.wikipedia.org/wiki/Flat_lens