Focal length 35mm equivalent, but not F-stop?

Started Jul 24, 2014 | Discussions thread
Lee Jay Forum Pro • Posts: 55,144
Re: Whoops!

Tim Tucker wrote:

Lee Jay wrote:

Tim Tucker wrote:

Are we just talking about noise generation in digital sensors here?

No, we're talking about the noise that's in the light itself (due to the quantum nature of light). And the signal to noise ratio that such noise generates on its own is equal to the square root of the total number of photons. More SNR = good, therefore more light = good. More light comes from either brighter light (faster f-stop) or more capture area (bigger sensor). Given the same f-stop, a sensor with 16 times more sensor area will capture 16 times as much light and therefore have four times the signal to noise ratio, which is the same as if the small sensor had been using an f-stop four stops faster with the same shutter speed.

IOW, FF 1/60th f/8 = 4x-crop 1/60th f/2, as far as signal to noise ratio goes.

Now that's not something that I've ever thought of before.

But I can see that you are right, QED backs this up and I will take your word on the maths.

You can read about it here:

http://en.wikipedia.org/wiki/Shot_noise

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