Parent (sudosysgen) is correct, I don't know why they're being downvoted. Another way to look at it is, if you have two setups with different sensor sizes, but

Parent (sudosysgen) is correct, I don't know why they're being downvoted. Another way to look at it is, if you have two setups with different sensor sizes, but the same relative aperture (i.e. f number), same ISO, same sensor resolution, and equivalent focal lengths (i.e. scaled by crop factor), you will have more noise in the image from the smaller sensor. As the parent stated, this is purely due to physics: the lens in the setup with the smaller sensor has a smaller absolute aperture; thus less total light is entering the camera.