Is my thinking about equivalence right?

Started 3 months ago | Questions thread
OP Muster Mark Contributing Member • Posts: 588
Re: Is my thinking about equivalence right?

dkyl wrote:

Muster Mark wrote:

Just look at the lenstip data. The Sony 50mm 2.5 has vignetting of 2.29 stops in the corners. The olympus 25mm1.2 has at most 1.3 stops of vignetting. Th Sony GM 50 1.2 has almost 3 stops of vignetting wide open.
Normal equivalence would say FF at 1.2 is gathering 4x the light as m43 at 1.2. That's not true if it's falling off so much more. Is the difference big? No I don't think so. I don't think most people care so much about vignetting, but it makes the "total light" calculation rather different.

Sure, but you're cherry picking a little here. The Sony 50mm f/1.2 is excellent but one of its design consideration is keeping it relatively compact. So of course something has to give.

I know you wanted to limit the scope of comparison to just Sony since it makes things a little easier, but if you expand your scope there are plenty of examples where FF is not any more prone to vignetting. It's just a design compromise depending on what the designers want to achieve.

Take the Nikon Z 50mm f/1.8 S as an example. Lenstip didn't do a review for the Nikon but DXOMark has a measurements for both the Nikon 50mm f/1.8 and the Olympus 25mm f/1.2.

The Nikon has a T-stop of T1.9 and vignetting at -1.6EV whilst the Olympus comes in at a T-stop of T1.8 and vignetting of -1.2EV.

So now they have practically the same transmission in the middle and only 1/3 stop difference on the peripheral whilst the Nikon covers an imaging area 4 times the size. And the two don't differ that much in size either.

I'm not here to preach FF or anything. I'm happy using both my m43 and FF gear. At the end of the day there are benefits to both system when looking at actual lenses and cameras that are being produced, not just theoretical benefits.

All very good info! My point was just to demonstrate the kind of analysis you need to do to actually compare total light of an exposure and why the equivalence formula (pupil area x sensor area) doesn't actually work in practice.

That Nikon in particular looks like a good argument for the system. It's nice to see weather resistant lenses/cameras becoming the norm.

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