I'm still playing with my Christmas "present" - a Gossen Lightmeter, today with the 5-degree spot-metering function. I notice quite a difference between the readings even though my cameras have a 5 or 6 degree spot size. They are both fixed focal length, so no variation in spot size. For example, the Gossen recommends 1/1000 sec, the camera recommends 1/400 sec. That's a big difference to my pedantic mind and is not explained by differences in K-factors, nor by different ISO speed definitions ...
Help! Anybody know why I can get over an EV difference with the same light, same subject, same time, same ISO, same f-number? Have I missed something during my long journey through Exposure 101?