Hi Jon Schwartz here. I work in professional fishing phototography, shooting jumping marlin and sailfish. The images are for magazines that only want tack sharp work. I use D700's with MBD10's. My go-to lenses were the 70-200 2.8VR's and the 24-70 2.8. Here is a shot of me posing with some of that gear (not that you need to see it, but it might help set the stage) In real life I am usually way off balance, looking like a kook and banging into things, with the boat rocking and rolling and spray everywhere. The 24-70 is a great lens but it froze up on me after getting knocked badly one time and the tech told me it's not repairable. I have since rented the older 28-70 (not made anymore) and liked that a lot more because it seemed more durable, but I'm not sure if I am ready to throw more money into renting it on every trip, or want to buy another mid range zoom. Funny thing is, because the fish jump every which way in a very unpredicatable manner, it's very tempting to zoom out and shoot conservatively, because there is that fear I will not get the fish in the shot. So when I am using the 24-70, or more recently the 28-70, I keep having shots where the subject was too small in the frame. The range is actually enabling me to chicken out, and I am rarely shooting above 50mm on the 24-70 or 28-70. Editors don't like to crop much so I end up with all this unusable stuff. For example, this photo below. It's cool because it shows the mate in action too, but if I had not zoomed out, the camera would have focued on the fish, rather than the mate, and I may well have ended up with a very valuable shot. So I figure, why not just go with a 50 prime. I want recommendations on the best one for the following need: autofocus speed, period. Sure, I'll probably appreciate how a 1.8 or 1.4 will work even better than my other 2.8's in low light, but that's not what I am getting it for- I am getting it for chaotic daylight action where I want to freeze spasmodically moving, unpredicatable subjects, shooting from a platform that is pretty unstable. From what I've read there are not a huge amount of choices- looks there are some 1.8's and 1.4's with different letters after them signifying internal focus and whatnot. But when I read the reviews of the lenses by customers, it seems there is a great variety of opinion on which are the best for my needs- quick autofocus in unpredictable action. Thanks very much for your input! Jon Schwartz Fishing Articles, Photography, and Travel www.bluewaterjon.com Blog: Jon Schwartz's Blog: Fishing Articles, Photography, and Travel By the way, here is a recent shot that I took from the water (with totally different gear, of course, but I thought you might enjoy the shot). The fish was released in great shape right after the photo was taken.