That's the first time I've seen that!
That's the first time I've seen that!
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Very good point about the sensor acceptance angles. I'm also wondering if periferal illumination correction also might have had an effect in this case.No, because I always leave it switched off. And I just turned on the camera to double-check, and it was, and is, off.
The 'sneaky' ISO boost with fast primes it done to compensate for loss of light transmission through the microlenses over the sensor pixels that occurs at high incident angles of light. As such, it's specific to digital (vs. film), and more boost is needed for smaller pixels. The issue has been documented (and quantified) by DxOMark. It's not just Canon, by the way - Nikon and Sony do it, too.
Of course, you would expect the f/1.2 lens to be brighter than a f/1.4 lens but this is NOT what Fleetie observed. When the camera communicates with the lens, it boosts its internal ISO (without telling you) so that the f/1.4 image becomes brighter than the f/1.2.
Do you have simulate exposure or whatever it's called turned on for LiveView? When it communicates with the lens it may get more information and so might also apply the peripheral correction information (which generally will affected the outer portions of the frame, not the overall frame).
As for Olympus f/1.2, it should be brighter than a f/1.4. You're talking a full stop there, no duh it'll be brighter.
I did a comparison of those 2 lenses with the Canon 50/1.4. I found that the Canon is faster (i.e. brighter in terms of T-stop or light transmittance) than the Zuiko f/1.2 lenses. But there wasn't a lot in it.So there are people with taste for older glass on this forum too. I'd turf out your fungus lens before it infects others and recommend you try the Rokkor 58/1.2.... you will like it.
To business - I'm deeply skeptical that the T-stop of the OM 50/1.2 is slower than the EF 50/1.4. Although there should only be 1/3 stop in it, none of your cameras are capable of detecting light that comes from faster than f/1.6. The 7D (iirc used for your test) is not capable of detecting light from a cone faster than f/2.
Nevertheless, Canon cameras appear to register better sensitivity when coupled to EF lenses. This is because the camera knows that it's connected to a fast lens and silently boosts its ISO. Of course, it has no idea about the OM 50/1.2, so it does nothing and gives you a faithful measure of the detected light.
I tested this quite carefully - the trick is to partially rotate the lens so that the electrical connection is severed - it's real. Curiously, my ZE 35/1.4 and Sigma 50/1.4 lenses also appear to be faster than they really are...
Others tested the 50L and found it behaves like a 50/1.6 on a 1D4 / 5D2 and a 50/2 on a 7D. I can't speak to a 5D3 - I decided that I'd be upgrading when I got to be better than my camera.
Canon is not the only culprit caught up in this game. Nikon, Sony and Pentax were also caught cheating customers out of large aperture. Per my comments, my Fuji X-E1 doesn't cheat with SLR lenses (but I've no idea whether it does with fast Fuji lenses.)
Now all this returns to the question of which lens is sharpest wide open. Well, the short answer is they're all pretty good at f/1.6 and excellent at f/2. Since the sensor doesn't actually detect light from a fast cone, it can't contribute to the bokeh - but since it's inside the mirror box, it could bounce around and degrade the contrast. Bear in mind that there's more than half a stop between f/1.6 and f/1.2 so 30% of the light intercepted by the lens is bouncing around...
The OM 55/1.2 is soft when wide open and sharp at f/2. I'm not finished with it yet. typically $550+
The OM 50/1.8 is sharp at all apertures but has weird bokeh - probably a result of its rudimentary aperture control. That said, they can be had for about $30 and are compact, well made and robust.