When using a supplementary closeup lens on a prime lens do I need to make any ex posure adjustment? For example, a +2 diopter on a 150mm lens (focused at infini ty,) gives .3x magnification. If I gain that magnification via extension, I kno w it will require about 2/3 stop more exposure. Do I also allow the 2/3 stop wi th the diopter and then add any extension compensation, or is it really "free" magnification? Just wondering...with 35mm I've always metered TTL, and never needed to worry too much about this.