Anyway, the center spot filter is not needed with the 45.
The centre filter IS required on the 45, at f8 and lower. I.e, f8, f5.6 & f4.
I know some may disagree, but i can only share from my experience and say that i have shot alot of later afternoon/ low light work WITHOUT the filter at f8 and lower and have suffered some very bad darkening at the edges. Working with the centre filter almost eliminates this. (For the record, this is using SLIDE film, i dont think the filter is required at all using negative film)
There are people who use the centre filter on the 45mm at all apertures, even though the booklet for the filter states "Do not stop down excessively while using the filter". I have tried this, and have seen no negative effects whatsoever, even stopping right down to f22.
The Xpan 90mm lense however, DOES NOT require the centre filter.
And in answer to the original post, the cameras meter will compensate for the filter
. .Although make sure if your using a hand held to add +2 exp comp.