The subject line up there is a bit of a generalization, yet true for most cameras, be they DSLR or point and shoot. And not a lot of people realize this fact. Many of my students just assume the camera makes one determination about the lighting in the scene and that is that. If only it were that simple (and it is when you use Manual mode and don’t let the camera decide, but that’s another topic).
The truth is, most of the time your camera will alter the selection it has made for shutter speed, aperture and ISO (depending on which variable you have allowed it to control based on mode settings) because you focused in one spot or another. This happens often in the matrix or evaluative metering modes, when the camera is allowed to use all of its metering point as it sees fit. It will not happen when using spot metering, but can, occasionally, when using center-weighted. Concentrating on the full metering mode then, be aware of where you are focusing as that may not be where you want to meter. [read]