melcat Offline Upload & Sell: Off
|
MOJO-903 wrote:
Is there an explanation regarding better light capture even though the focal length and aperture are the same?
Although not often quoted for stills photography, lenses have a parameter called T-stop. This is like the aperture, but related to light transmission specifically, rather than depth of field. A lens with perfect light transmission would have T-stops the same as f-stops. Usually, it's a small difference. Even that matters for movies, which is why movie lenses are marked in T-stops rather than f-stops.
I have no idea what the situation is with your lens, but a Google search for "24-105 t-stop" (without the quotes) yielded this as the top hit:
http://www.dvxuser.com/V6/showthread.php?309352-canon-24-105-F4-not-an-F4&s=560d4c1858e907b22578f0c821a25667
It describes exactly what you're seeing. I don't know whether to believe it or not.
That said, the 24-105 also has a lot of vignetting, and who knows what the evaluative metering does with that.
Finally, Canon have a stupid "feature" for their fill flash in Av mode. It quietly adjusts the fill ratio you've set behind your back, by an amount that depends on the ambient EV level. I have no idea whether it's on in P mode as well.
|