sploo wrote in post #18005531
Thanks... but can you (or someone) actually quantify the advantages of BBF for my scenario? My understanding of the advantage is that you can focus recompose (because focus and shutter are on two different buttons), but, for my application I'd want focus to be running the whole time I'm shooting a burst, so the only difference with BBF is that the focus button would be held and the shutter button would only be pressed during the actual shooting burst. Maybe having the shutter button half pressed is slowing things down because the camera is metering all the time? (but it seems odd that would affect AF performance).
With BBF and AI Servo (both are very important parts of the equation) you press the back button to lock focus on your subject. Keep the button pressed. AI Servo (which is spectacular in the 5D3) will keep the focus locked on your subject, and as your subject moves it will continue to keep focus locked on your subject. The AI Servo in the 5D3 is so good that I can track an ice hockey player from face-off through an entire play and keep that same player in perfect focus, with my index finger poised on the shutter button, and ready to capture a series of shots. There is no waiting to lock focus. There is no wondering about focus. It just works. It allows for instant response.
There are a lot of ways to tweak AI Servo in the 5D3 to get the best performance for what you're shooting, but the AI Servo presets are the best place to start. I personally find that AF point expansion (4 points) really helps as well.
Now, here comes my "tough love" rant. I'm hesitant to do this over the internet as things can really get lost in the translation, but I'm hoping to put things in perspective for you. I don't want to come across as harsh, and if I was saying this to you face to face and you were able to see my body language and expressions this would be so much easier.
With my T1i and an EF 70-300mm f/4-5.6 IS USM shooting ice hockey (AI Servo, shutter button focus), my cull rate was 90% based on missed/soft focus.
With a 70D and 70-200mm f/2.8L IS II (AI servo, shutter button focus) my cull rate went down to 80% due to soft/missed focus. In changing to BBF and learning how to use it my cull rate due to missed/soft focus went down to 50%. That is really significant. I was skeptical about BBF, but the numbers don't lie. It worked.
With the 5D3 (BBF and AI Servo) and the 70-200mm f/2.8L IS II my cull rate due to missed focus is under 5%. Notice that I don't get soft focus anymore. I just get missed focus when I make a mistake. It happens when I've locked on to the wrong subject, and I'll lose a bunch of photographs in a row as I wasn't focused on the player I was actually shooting.
Let's sum that up . . .
I had the same focus hit rate with a T1i and EF 70-300mm f/4-5.6 IS USM as you do with a 5D3 and a 70-200mm f/2.8L IS II. Toddlers are not fast (I walk faster than they can run). They are very erratic (which is part of what makes them so challenging). Hockey players are fast and erratic.
With the same gear as you, I have a 95%+ hit rate shooting subjects that are just as erratic but much faster than your subjects.
You have asked for advice here and from and from a CPS professional. You are reluctant to follow that advice. You have very capable equipment. If you are not going to learn how to utilize it to best ensure your success you should sell it, pick up a Rebel, and put the left over funds in your children's college funds.
This is where I would give you a hug if you were here with me, and then we'd go out to shoot so I could teach you how to use BBF and AI Servo.
But, you aren't here. All I can do is ask you to please try it. Switch to BBF, remove focus from your shutter button, really invest the time in learning how to use BBF (it will seem really weird and awkward at first) and AI Servo. Ask for advice and help as you work with it. Don't let initial frustration push you back to the shutter button for focus. Once you get the hang of it, it will absolutely change your photography for the better.