Is my thinking about equivalence right?

Started 3 months ago | Questions thread
JosephScha Veteran Member • Posts: 6,622
Re: Is my thinking about equivalence right?

The idea of equivalence is to have the same angle of view, and the same depth of field and the same time of exposure so that the pictures are as indistinguishable as they could possibly be.  Any difference, therefore, is attributed to the efficiency of the sensor ... now that is the point I think you are arguing, and you have a point.  If the lenses are not both really the same then equivalence may not really work.

Anyway, let's assume Micro Four Thirds has the 25mm f/1.4 at f/1.4.   A full frame camera would have to have a 50mm at f/2.8.  Now no one actually SAID anything about the same amount of light, it's the same depth of field that makes FF use f/2.8.  And you probably noticed, in order to have the same time of exposure when two f stops reduced, the FF camera would have to use a higher ISO.  So the FF really is capturing the same amount of light, and spreading it out over a larger sensor.

Now, a good question might be, what does this prove?  It is supposed to compare the efficiency of the sensors.  If they are both the same, both will have the same amount of noise.   If one is more noisy than the other, then this test may have proved something about the cameras being compared.

That's all that equivalence is about.

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