I've been using a Sekonic L508 for years. I've noticed that it reads 1/2 stop slow when comparing it to "sunny 16" i.e. it will read f16 and 1/2 at 1/125 rather then an even 16 when I use FP4. However, when I take the iso down to 100, it then reads an even f16 at 1/125. The difference between iso 125 and 100 is about 1/3 of a stop correct? So is my meter under exposing? I normally down rate my film at half the box speed anyways but still my negs look a little thin in the shadows. Thanks for replies.