Light gathering in M43 vs FF

Started Nov 25, 2012 | Discussions thread
Klarno Veteran Member • Posts: 4,148
Re: Light gathering in M43 vs FF

Peng Bian wrote:

So there's a lot of discussions regarding FOV of M43 vs FF, and I think I have a good grasp on that aspect.

Thought one thing that bugs me is light gathering. Let me ask the question with a simple example:

Suppose I have two camera setups:

  • 25mm f1.4 lens on a M43
  • 50mm f1.4 lens on a FF

Same scene, same placement, shot wide open at say ISO 200. Assume that processing between the cameras is exactly the same, I set the exposure to 1/100, will I get the same image in terms of amount of light gathered?

The important thing in any electronic signal capture--regardless of whether we're talking about photography, or audio recording, or any number of other things--is signal to noise ratio. It's simple: the more signal you have going into your end result, the less noise there is.

For your parameters, you get the same amount of light per unit of area, which maintains the same exposure. However, due to the differences in total area of the sensor, the FF setup gathers about four times as much light, meaning you have four times as much signal going into the image. Which means the noise that's present is less evident, by a factor of about two stops, for sensors of similar quantum efficiency.

You also get half the depth of field on the FF image.

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