Speaking of how dark it is in my cavernous family room....how do I determine that? If I take a meter reading is there some formula that tells me what the EV is? I will play today with the f/2.8 glass to see if there is a discernible difference between it and the f/4. I guess common sense says it should be who knows! If I'm feeling truly adventurous maybe I'll throw in a fast prime for good measure :-)