Well, the reason is that the A1's matrix mode algorithm uses the
overall EV to determine scene type. If, for example, you are shooting
in bright sunlight the camera understands that and will use that as a
baseline for exposure determination. If you do a closeup of a white
car with bright chrome, the camera will understand that it is being
fooled by too bright of a subject and will fall back on its baseline
exposure that is programmed in for bright sunlight.
If you place a polarizer or ND filter on the lens, the camera is
fooled by the lower EV value and no longer correctly understands the
scene. When confronted by that same white car with bright chrome, the
camera will end up underexposing the picture because the EV value is
not interpreted correctly and will fall back on standard
focus-point/surround evaluation and ultimately to just overall
average.
Minolta and Nikon use almost identical methods for 3D matrix metering.
The difference between the A1 and the Nikons is the knowledge of the
lens itself. The A1 understands distance as well as the actual
characteristics of the lens. The lens characteristics are hard-coded
into the algorithm. Nikon, in the (D)SLRs, will make use of the
distance information in some lenses, but the EV is determined
relatively.
Except for that one nuance, I will say that the A1's auto-exposure
metering is the best I've ever used in any camera. It really is that
good. In all honesty, I think the ESP mode in the IS-3 did better than
my E-1 too.
AG
> The A1 uses contrast detect autofocus as do other digital P&S. In fact,
> I think all cameras that can focus in live view mode must be using
> contrast detect and would likely not be affected by linear polarizers
> (other than cutting the amount of light they have to work with). I
> thought the A1 also measured exposure from the sensor as well so I don't
> understand why that would screw up the matrix metering.
--
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