I just got my polarizer (linear) a week ago and I decided to go have uber-saturaty good time. I heard that it had a filter factor of 2-2.8 or so which means, if I am not mistaken, that you must increase the exposure 1-1 1/3 stops over the same shot w/o a filter. For some dumb reason I didn't bother to test this out because I noticed that the ttl meter read the scene as darker with the filter on, thinking that it would meter for the correct exposure. I shot off 5 rolls before getting them developed, 2 at sunset one day, and 3 at sunrise the next day. The first roll I shot off at sunrise a roll of 400 shot w/o my polarizer. Those came out correctly exposed; I then shot off 2 rolls of 100 with my polarizer, forgetting to change the iso setting to back down to 100. It dawned on me later on while I was at work what I had done when I was looking for something in my camera case (I don't trust the sun enough to leave it in the car!) and found that the iso setting was at 400. I actually clocked out and hauled butt down to Walgreens to see if they had already developed the film and if not, if they could correct the problem. Unfortunately, they had developed it a while ago (I'm buddies with them over there now , they develop my film before everyone else's). To my complete and utter amazement, the rolls of 100 the day before came out terribly overexposed, and the rolls of 100 shot at the wrong iso seeting came out less than 1 stop underexposed. Soooo...long story short: do ttl meters generally read a scene overexposed? I sat thinking about that and the filter factor thing, and it made my head hurt. Come to think about it...I guess I could just test this out right now :roll:... well, I've typed too much to delete it, so entertain me with your replies.