makes focusing a whole lot easier and with the split itching now being double sided compared to the original single itch, you can now use both slow and fast aperture lenses without a problem.I got this for my Canon 1D Mark IIN and when other people complaine about there cameras not able to focus in ultra low light, i just keep on shooting, if you got a lot of fast primes; f/1.2, 1.4's, and shoot in bars, parties and at night, this is for you.