In praise of Panny's 2.8 zooms

Started Jul 30, 2013 | Discussions thread
EEmu
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Re: In praise of Panny's 2.8 zooms
In reply to SDPharm, Jul 31, 2013

SDPharm wrote:

You're right on the amount of light per pixel. What I meant was, the light gathering capability of a FF lens is the same as a M43 lens per unit area on the sensor.

That is correct.

If you complete the reasoning, however: FF is four times larger (area) than M43. Thus, same light per unit area * 4x the area = FF has 2 stops more light.

It therefore follows that a f/5.6 on FF has the same light gathering ability as f/2.8 on m43. If you don't account for this difference in your comparison it is wrong.

For example, in a given scene, if you set a camera at ISO100, and set the same aperture, let's say F4, then it does not matter if you use a FF or M43 camera, the exposure time will be the same (or close enough). Are we agreeing on that?

Correct.

F4 is F4 in terms of exposure. That's what I meant it's a wash.

Technically correct, but massively misleading.

When exposed for the same time at the same aperture the FF is exposed to 4x the light because it has 4x the area, as shown above. Because noise follows light received to a very good approximation, the FF will have less noise (2 stops).

If you instead expose the FF with double the aperture it will get 1/4 the light over 4x the area and thus have the same exposure.  Same amount of light: same noise.

Yes, you will have to increase the ISO to get the FF to be the correct brightness but that has no impact on image quality.  It just makes it look brighter.  (This is in theoretical manual mode because we are controlling all three variables.)

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