| Marc: I've said as much in my post :
"For A lenses, the exposure is mesured wide-open, then calculated for the given aperture you want to use, so selecting f/2 will always gives half the speed of f/1.4."
But now, think about the following experiment:
- take a 50/4 and a 50/1.4 PKA lenses...
- check exposure on both at f/4 (in full A mode, not stop down)
- you'll see a difference, as the f/1.4 lens will heavily underexpose wide-open, and this will be propagated on all apertures you select on the body.
This can be extrapolated to all lenses... The "Highlight saving"/underexposure amount is dependant upon the largest aperture of the lens.
I'm pretty sure those A* 1000/8 lenses do overexpose...
Flyer : I'm not talking about linearity against amount of light coming in (of course, at a given aperture, twice the light results in twice the speed), but linearity against the aperture used.
Focus screens are in fact no longer just ground glass, but are now fresnel lenses... Those fresnel lenses are designed to optimize light transmission for given apertures, and so are not aperture-linear anymore.
LL80 focus screen family are designed to increase perceived brightness at any aperture above f/5.6... And this results in an underexposure. And, negative point of this design, aperture below f/5.6 (rarely seen in PKA lenses) now suffer of a darker viewfinder, and thus an overexposure... |