"Equivalence" demonstrated: Canon 5D and Panasonic GX1

Started Apr 27, 2013 | Discussions thread
JosephScha Veteran Member • Posts: 4,909
Re: "Equivalence" demonstrated: Canon 5D and Panasonic GX1

Re: "many people would seem to doubt this simple fact"

Yes, and that is the worst part about this ongoing discussion of "equivalence". It is not intuitive that what they mean by its definition CAN NOT include equivalent exposure.  It confuses many people who think equivalence must include equivalent exposure.  They assume it does, and somehow think that f/4 on full frame needs f/2.8 on m43 for exposure reasons.  That is absolutely not true, those people have been misled.

By using the same aperture diameter (instead of f stop) and the same shutter speed, the "equivalence" crowd are achieving the same total light reaching the sensor, which means that the larger sensor has less light per unit area, that is, less exposure. So to make up for that, the system with the larger sensor has to raise ISO ... So IF the sensors are equally efficient then the noise will be the same.

Since the two systems use the same aperture diameter they will have the same DOF.

Since they have the same shutter speed they should have the same motion blur.

And of course the framing and display size should be the same.  This clearly means that they don't compare 100% view, because that would not be the same display size for two sensors with different number of megapixels.

So I think they do have a point about comparing pictures which SHOULD be indistinguishable, so if they are distinguishable you can say something about the two cameras.  The pictures you posted (which have same exposure, that is same f/stop and same ISO) are easily distinguishable, the one with much less depth of field is the SLR.  Of course what JJ (GreatBustard)'s definition of equivalence is tries to take away that possible advantage of an SLR by asking how it does with the same aperture diameter, not the same f stop.  And that's exactly what is non-intuitive ... "but, you COULD use f/2 or even less on a DSLR and stay at base ISO"  ... yup, you could.  Equivalent exposure.  A very comfortable concept for me.

The stretch is to try to grant that the other definition of equivalence might have a purpose, and does not need to be shot down or decried. No one is forced to use it to compare systems, they are just proposing that would be a good way.  And it doesn't take into account features like autofocus speed, movie modes, anything like that, which people will consider.  It's just one proposed way to compare.

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