Too bad you don't own one as it is easy to check. Good point that you brought up reading off the film plane as in fact it has a backward looking sensor that it could possibly meter after the mirror is raised but apparently that is only used by the TTL flash.
Originally Posted by LiamG
Unfortunately I don't have the magazine review of the FG that may have detailed out the sequence like it did for the OM2 but it is easy enough to test. So I did the exact same test as before except that this time I covered the backward point meter cel in the box. Meter wide open it fires at a fast shutter then stop the lens down - meter is unchanged as the tab is not actuated, but shutter is much slower when fired. Conclusion is therefore that it must takes one last look at the meter prior to raising the mirror.
BTW, the whole sequence would still take the same time whether if it looks at the meter prior to raising the meter or after by reading off the plane. Since these are no longer CDS cels, metering is fairly instantaneous.