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I am planning to start using a light meter for portrait photography with an Olympus OMD EM5, off camera flash and an old Canon 135mm f2 manual lens. However having read about it, I think that I will need to adjust the meter reading to the micro four thirds equivalent values.

So, if the equivalent f value is double on the micro 4/3, does it mean that I need to use the exposure time shown but divide the f value from the light meter by 2?

For example if the light meter shows 250 / f4, I would use 250 exposure, but set my lens to f2 (instead of f4).

Can someone confirm whether my logic is correct?

marked as duplicate by mattdm, TFuto, MikeW, AJ Henderson, Philip Kendall Oct 7 '14 at 9:28

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No. As far as exposure value goes, an f-stop is an f-stop. It's only where depth of field is concerned (and noise calculations derived from "total light captured", if you're the type who has to go there) that you need to think about equivalent f-stops.

So if you are reading 1/250 at f/4, set your camera to 1/250 at f/4. That will give you a correctly-exposed picture that is the equivalent in terms of field of view and depth of field as having used a 270mm lens at f/8 on a full-frame (35mm format) camera (to a first approximation).

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