How important is f2.8 on 40D

With the purchase of my 40D, I am wondering how important is it to have a f2.8 or faster lens to take advantage of the better focusing in the center focus point. The choices of lenses for walk around that are 2.8 or faster are slim. I have three in mind, 24-104L, 24-70L or 17-55 IS. Focus is so important to me though that I woundered what has been your experience with better focus with faster glass. I know L is best but.......

If you don't need a fast lens for the exposure, you probably don't need it for focus either.

The 40d focuses plenty fast with f/4 lenses, and even my 100-400 focues better with my 40d than it did with my XTi.

JohnC

I guess I was wondering if the hype about the center point and 2.8 resulted in more accurate focus. I can't imagine that it could be because the 40D is so good with focus accuracy. Just wondering do I need all 2.8L glass. (dream)

OK, so I'll back up a bit. What are you trying to shoot? For static or slower motion subjects, you would have no problems with focus accuracy on a 40d. It AF's fast and accurate at f/5.6. If you're shooting fast moving sports or wildlife, you would take better advantage of the AF system with faster glass.

I've shot wildlife with a f/4 and f/5.6 lenses, and the 40d locks/tracks just fine. But, it is better with an f/2.8 lens, naturally.

If you're just looking for a push, then: Yes go buy some new fast glass, you NEED it.

JC4 wrote in post #5025811
If you don't need a fast lens for the exposure, you probably don't need it for focus either.

The 40d focuses plenty fast with f/4 lenses, and even my 100-400 focues better with my 40d than it did with my XTi.

JohnC

John:

I can give you some perspective. I started with an XT. I upgraded to a 30D and I do mostly sports shooting. I have two 2.8 lenses. The 30D focusing is better than the XT, but not a great deal, However, the 40D focusing is MUCH better than the 30D, and WORLDS better than the XT. I shoot lots of running, biking, and baseball/football. My keeper rate went up slightly from the XT to the 30D, and my keeper rate went WAY WAY UP from the 30D to the 40D. So, from my experience, and for the type of stuff I photograph, it definitely made a difference for me! Also, when I use my 28-135 (rarely), my keeper rate falls below what I get from my 2.8's. Hope that helps!

I'm not the OP SantaB. You're agreeing with me. The XTi has the same focus system as your 30d, so the jump in performance you and I saw from 30d/XTi to a 40d was similar. And thats with the same lenses. Thats one of the points I was making to the OP. The 40d will perform VERY well with any lens. Buying f/2.8 lenses will just improve on that, but not as much as the body change itself. And, like you indicated, with your sports shooting experience, f/2.8 is well worth it for such subjects.

newtune3 wrote in post #5025794
With the purchase of my 40D, I am wondering how important is it to have a f2.8 or faster lens to take advantage of the better focusing in the center focus point. The choices of lenses for walk around that are 2.8 or faster are slim. I have three in mind, 24-104L, 24-70L or 17-55 IS. Focus is so important to me though that I woundered what has been your experience with better focus with faster glass. I know L is best but.......

Not to nit-pick, but the 24-105L is F4, while the other 2 pieces of glass are F2.8. Alot of people seem to like the 17-55, but if that's not enough reach for you, the 24-70L works great on the 40D [I have this combo on mine most of the time]. The 24-105L has IS, so it's a nice option too

I have experience with the 20D/30D/40D, 17-55, 24-70L, and 24-105L. The 40D focus system is WORLDS better than the 20D focus system. It's quite astounding how well it can lock onto a black suit, in a dark room, with very little ambient light. Where the 20D would seek the 40D locks on. I've not used a 3xx/4xx camera so I can't compare them.

I've only used F2.8 lenses on the 40D, but comparing the three lenses above I don't see a lot of difference. The only real difference is IS and focal length. There's one stop in it, the difference between ISO400 and 800 or even 1600 and 3200 isn't major. Having said that given I photograph weddings I wouldn't want to have lenses slower than F2.8. For most people this won't be important, since the center cross type focus point of the 40D is rated at F5.6.

In summary - the 40D rocks, it's a major advance on the 20D/30D for people who earn a living from their cameras. The keeper ratio jumps because of the new AF system. The 17-55 rocks so hard I have two of them - just in case on fails (it's not the most reliable lens in the world). The 24-70 not so much - no IS and a bit long on a 1.6 camera. The 24-105 F4L rocks if you have enough light. On a 5D the 24-105 is the sharpest combo i've ever seen, it's astounding, almost to the point gaussian blur is needed.

Thanks to all for this in depth look. Canon goes on about the center point and f2.8 but I am at the same place as most of you. I am so happy with the focus of the 40D. Keeper rate is so much better. I am finally shooting RAW completly and wow. I will let you know when I buy the next "L". Thanks again for you time and opinions.