Alternativly you can set exp. correction to minus 1, which will give you the
same result= underwsposing the "1600-film" by one stop or the same as
shifting to 3200 ASA.
Not quite the same result. Because you're underexposing by a stop, you'll lose one bit (out of twelve) of sensitivity. If you're shooting JPEG then that's almost definitely not a problem, but if you're shooting RAW it may be. Although it's likely that that bit is well below the noise floor anyway...
More practically, you'll need to boost the brightness in Photoshop to take the underexposure into account - that's not necessary if you set the sensor to ISO 3200 to start with...
S
