How many extension tubes needed?
I have a Canon 12 mm extension tube (EF II) and a Canon 25 mm EF II on order. I like to shoot macro of coins and bugs. I've noticed an online classified ad in my area for another 12 and 25 (same tubes) for an amazing price. If I am going to be working with a 50mm lens, should I add to the 37mm tube length that I'll have? I could buy either the 12 or the 25. This deal won't last.