In my 7D manual it clearly says "evaluative" metering does what it's supposed to do but when I use single point AF and choose an AF point in a darker or brighter area of the scene it adjusts the exposure. If the camera does not change position should the exposure not be the exact same when set to evaluative? It seems to change from the evaluative to spot. The AF spot. Is there some way to prevent this besides using AE lock? Thanks.