f/1.8 on m4/3, ASP-C, FF; are they the same?

Started Nov 1, 2010 | Discussions thread
Stelyn
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Re: f/1.8 on m4/3, ASP-C, FF; are they the same?
In reply to Peiasdf, Nov 1, 2010

Peiasdf wrote:

Hi everyone, I do not get why some people said the 20 f/1.7 lens on m4/3 equals to 40 f3.5 on FF so here is the thread asking about it.

If a picture is taken at 20mm, f/1/7, ISO 200, 1/100s on m4/3, will it come out similar (beside DOF) to a 40mm f/1.7, ISO 200, 1/100s picture on a FF?

Some people mentioned m4/3 lens only lets in a quarter the light of a FF lens. So does it mean the camera have to reduce speed by a factor of four to get the correct exposure. It does not make sense to me, as P&S cameras do not require 15 times the exposure.

I am thinking about going from D90 + 35 f/1.8 -> GH2 + 20 f/1.7 for a night out with friends camera but the exposure thing is throwing me off. Maybe I need a Nokton 25 f/0.95?

LX3 @ 40mm, ISO800, 1/30, F3.0
GF1 @ 40mm, ISO800, 1/30, F3.0
FF @ 40mm, ISO800, 1/30, F3.0

These would all expose the image more or less the same. However, the LX3 would show the most noise and have the largest DOF, then the GF1 and finally the FF cam would show the least noise and have the shallowest DOF. Noise levels assume a similar technological state of advancement of each sensor, which is rarely the case in practice. The DOF is bound by the optical laws of physics and so is pretty much immutable.

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