The truth about fast glass on m4/3

Started May 21, 2012 | Discussions thread
Iskender Senior Member • Posts: 1,328
Re: Who cares about the total light flux

simpy wrote:

Actually, f-numbers are a pretty good way to talk about sensor illumination. Not considering macro photography, they define the angle of the light cone hitting the sensor, and by that, the illuminance. For an object of luminance L, it's given by:

[sensor illuminance = intensity] = sin^2(theta) π L = π L / (2 f)^2

where f is the f-number. EVs are only useful if you also supply a reference ISO value (typically 100; acts to set a target value in lux second) and a unit of time (usually seconds), in which case it becomes a logarithmic measure of L.

I agree that sensor performance varies. However, scaling by sensor area is a good first approximation that holds relatively well for same-generation cameras. Check out the DxO curves to see this in action. Of course there are differences and they matter when shopping for a particular camera. However, when you decide to buy a lens that will outlast a body you may want to take the general scaling into account.

I don't really have much more to say - we basically disagree but you argue politely and reasonably for your point which is too rare in a forum like this - it is appreciated. I can kind of see the appeal.

For me the main drawback has to be the confusion the "aperture method" causes - I think it's more educational to consider the lens and camera separately, so that one can be learned at a time. When these things are mixed together we get confused people who get thrown off when they just want to take a photo.

So it still feels like halfway solution to me - when someone just wants to take a photo with a specific camera it throws in unnecessary comparisons. When on the other hand a new camera generation is released it's not universal to that, but has to be built again (if I understood correctly.)

I'd still like to see camera performance expressed as "can expose correctly in time x at x EV" or some similar way, the same way dim light autofocus is expressed. I realize there are hurdles to be overcome with such an approach too. But mostly I'll just say "to each his own" since this little corner of the thread has managed to stay so nicely civil.

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