f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
D Cox Forum Pro • Posts: 22,081
Re: f-number equivalent between m43 and FF

goshigoo wrote:

Just read the thread about the new 15 f/1.7; I see people saying f/1.4 is f/1.4 regardless of format

I do agree with this statement on the meaning of f-number, but it is confusing since it is the format + f-number which determines the amount of light captured by a picture, which accounts for the final Signal-to-noise ratio of a picture

The final SNR depends (assuming technology of the same generation) on the amount of light falling on each pixel. This determines the uncertainty of the measurement of light by that individual photodetector. The more photons, the more certain the measurement.

The signal in a photographic image is the differences between pixels. The uncertainty (error bars) for each pixel gives a random, or noise, component when comparing the pixels.

The total area of the sensor is irrelevant. If you put the same lens on various sizes of sensor, the noise level in the part of the image that they all record will be identical. (Assuming they are the same generation of technology.)

we should really comparing 25mm f/1.4 @ m43 vs 50mm f/2.8 @ FF
as they both yield the same View of field, DoF, Signal-to-noise ratio of the final picture and the lens size should be comparable too

Should I think this way?

Not really.

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