Is FF sensors going to slowly phase out?

Started Apr 11, 2013 | Discussions thread
EinsteinsGhost
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Re: it depends on your definition of 'slow'
In reply to forpetessake, Apr 15, 2013

forpetessake wrote:

EinsteinsGhost wrote:

tomtom50 wrote:

EinsteinsGhost wrote:

forpetessake wrote:The f-stop determines the brightness, but you need to integrate over the area to get the total light, collected by the lens, and that's exactly what determines the photon noise part of S/N ratio.

Nope. Larger sensor uses more light (for a wider FOV), but the light falling on the sensor over the same surface area as a smaller sensor doesn't change.

I think you are talking past each other. forpetessake is speaking of brightness in the sensor of lux, lumens/area. It is correct that lenses of equal aperture deliver the same lux, and since lux is lumens per unit area more area means more lumens.

This is a main reason a larger sensor tends to outperform a smaller (I wrote tends, many exceptions exist) sensor. Photon shot noise is related to the number of photons falling on the entire sensor for a given output scale.

If we put a 50mm f/1.4 lens in front of a 35mm sensor, and then replace the sensor with m4/3 sensor, the extra light simply goes unused. The exposure value will not change (outside of metering differences potentially due to a tighter FOV).

Now, how useful is that experiment? Would you put 20mm f/2.8 on FF and 200mm f/2.8 on m4/3 and compare them? Well, I have the answer: they are completely different

When people discuss equivalent systems they want to get the same FOV, otherwise what's the point of comparison.

The purpose of the "experiment"? Pointing at the ill-conceived idea of f-stop coupled with crop factor for exposure as well.

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