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New Voigtlander Nokton 50mm f/1.2 Aspherical
(07-21-2018, 06:56 AM)Brightcolours Wrote: With digital, it is the sensor that limits the amount of light being used with bigger apertures. You can't call that T-stops.

Can you explain, I didn't understand (seriously, and I am not trying to troll)
Just what I said. With digital, light gets lost with light hitting at steeper angles at the micro lens structures. You see this as vignetting with (U)WA lenses, and light loss at large apertures. With every f1.2 lens you won't get f1.2 worth of light. Or: with every T1.3 lens you won't get T1.3 worth of light. Reason: the micro lens structure. You can test this yourself: put your f1.4 lens on your 5D. Use a fool proof metering mode, and meter what light it needs wide open. Now disconnect the lens a bit so that the contacts don't make a connection. Now the camera does not know it has a 50mm f1.4 lens. Meter again. You will notice a slightly different (longer) exposure time.

With bigger apertures, Canon amplifies the signal extra to hide the confusing fact of light loss at microlens level with big apertures which does not cause is shorter exposure times even though you do use a larger aperture which does allow more light to get through.

Hence: you can't say that that 35mm f1.2 has the same T-stop as the 35mm f1.4 because the exposure times are similar.
Or think of it this way, even if you set your lens to f/1.4, let's say your lens has 2EV vignette. That means even if your lens is a theoretical T/1.4 lens, you are getting T/2.8 at the corners. The same lens on a film camera would probably have less vignette.
It is not just light loss in corners. With big apertures, every part of the image gets light from every spot inside the aperture, the bigger the aperture the bigger the angles of part of the light. That is what causes the longer exposure times than expected, even when you meter just in the center.

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