# Maximum resolution per lens size

This question is more practical than theoretical, but I am interested in the theoretical considerations as well.

My wife just bought a Samsung S3 phone with a 8 MP image sensor hiding behind a tiny lens. In daylight the pictures come out fine, but it suffers horribly in low-light conditions. Is there a theoretical limit as to how fine an image sensor can be behind a lens of a specific aperture, given a reasonable amount of ambient light and a reasonable shutter speed? Will increasing the sensor resolution beyond this limit decrease the actual resolution (the ability to resolve two points as individual points) of the final image?

Thanks.

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$$\Delta \ell = 1.22 \frac{f\lambda}{D}$$
where $f$ is the distance from the plane of the lens to the detector, $\lambda$ is the wavelength of the light and $D$ is the camera aperture. Making the pixel size smaller than $\Delta \ell$ won't do any harm, but it won't make the pictures any sharper.