Focusing Issues w new 70-200/2.8 II IS

sara505

99% of my shooting - for many years now - is done with the center-spot-focus/recompose method. I'm noticing that this is not working so well with my new lens. Is it me?

kdog

sara505 wrote: »

99% of my shooting - for many years now - is done with the center-spot-focus/recompose method. I'm noticing that this is not working so well with my new lens. Is it me?

Probably, but hard to say for sure without an example. You know that in general, focus-recompose has a built-in focus error, right? It's not normally a big issue at nominal DOFs. However, the paper-thin DOFs resulting from using wide apertures on a telephoto lens is a worst case condition for focus-recompose and can definitely mess up your shots. It sounds like that's what you're seeing.

sara505

kdog wrote: »

Probably, but hard to say for sure without an example. You know that in general, focus-recompose has a built-in focus error, right? It's not normally a big issue at nominal DOFs. However, the paper-thin DOFs resulting from using wide apertures on a telephoto lens is a worst case condition for focus-recompose and can definitely mess up your shots. It sounds like that's what you're seeing.

It's not really a DOF/focus issue, per se. What's happening is, the focus does not lock. I focus by partially depressing shutter, recompose, and the camera decides to focus elsewhere.

I should mention I'm shooting with a 5dMkII, have had similar issues with auto-focus, especially in low-light or low-contrast subjects. But the above-mentioned issue happens in broad daylight.

novicesnapper

Check and make sure the camera isn't on servo mode, which is constant focus adjustment.

sara505

novicesnapper wrote: »

Check and make sure the camera isn't on servo mode, which is constant focus adjustment.

That was exactly the problem (so easy to bump those dials, it requires constant monitoring, like flying a fighter jet, I find :-) ) Thank you! bow

novicesnapper

Lol cool. I always have to check mine, when I'm in there diddling around. The servo mode is usually used on moving targets, to maintain the focus. A guy on a bike riding towards you for example.

sara505

novicesnapper wrote: »

Lol cool. I always have to check mine, when I'm in there diddling around. The servo mode is usually used on moving targets, to maintain the focus. A guy on a bike riding towards you for example.

Okay, I've been shooting with Canon for years, and never used that mode. - will have to check it out now that I know what it does.

novicesnapper

Haha, on spot metering and servo, you will always be chasing the focal point. If you're subject moves out of the spot focus, the lens will hunt madly for the next focal point to hit. I hardly ever use it, wears me out lol. I would rather refocus on every second or third shot, on a three shot blast in single focus and spot meter mode. I also can't help but wonder how hard it is on the focus motor of the lens. I just discovered live face monitoring on live view, on my T1i the other day, kind of freaky lol. I'm still trying to figure that one out lol. To watch the facial box move following the subjects face without touching the camera . Two years later, I'm still learning the camera lol.