Rebel xTi - AI Servo Mode only continue focus on center focal pt??

[HeyThereChelle]

I've been slowly working through some AF issues that I've been having with my camera, trying to figure out if the problem is user error or equipment malfunction.

Through much playing I found out that my camera does not continually focus when set in AI Focus or AI Servo unless the focal point is manually set to the center point. I prefer the corner points so I can focus on the eyes and not have to focus then recompose.

I can't find anything on this in the manual that says AI Servo only works on the center... Is this a malfunction in my camera or just the way it is?

[Doug Pardee]

AI Focus is useless, so just forget about that one.

AI Servo should work okay with any of the AF points. However, only the center point is a cross-type; the other AF points are only sensitive to edges in a particular direction. Also, if you're using a fast lens (f/2.8 or faster) the center AF point has three times the precision of the other AF points.

(You didn't ask about it because it's not what you're looking for, but if you have all AF points enabled AI Servo starts with the center AF point and attempts to track movement of the subject to the other AF points. That tracking rarely works on the wide-spaced AF points in the Rebel series.)

[HeyThereChelle]

I was playing with my friends Nikon D80. When in Servo mode (can't remember what Nikon calls it), I could focus on a particular subject then move the camera around the room and you could hear the lens continually re-focusing on whatever the lens was aimed at.

My camera - nope. In AI Servo mode, the lens would focus once then not again no matter what I aimed it at. Unless I had selected the center focal point. Then you could tell the lens was focusing even as I tracked a subject or moved the camera around.

If I leave my camera in One Shot, I'm getting decently focused pics most of the time. (I'm trying so hard.) But if I switch back to AI Servo, I don't have a chance in heck to get a focused shot unless the center focal point is selected.

sorry if I'm being redundant. I do understand that the center focal point is more accurate in wide open apertures. But is it normal for the other focal points to not work in AI servo?

I took my camera into the shop where I bought it and they were rather undecided as to whether I should send it in or not. I really don't want to be without a camera for a month, so I said I would keep practicing and get back with them about sending it in. Then I found out about AI Servo not tracking except for the center. The guys at the camera shop were not so helpful and I really want to get this figured out before holiday pictures. I've missed out on so many shots already due to focus.

[spencer28n]

AI Servo was built to use the center AF point because it is the most accurate. The concept behind AI Servo is tracking movement, mainly sports. It's not concerned about the perfect focus of composition but in getting the shot when you need it.

[momtoamiracle]

al servo is useless. I was getting terrible focus till I switched to one shot and then I could use the focal points.

it talks about it some in the digital field guide for the xti. can't remember what it said, but it made me realize why my 50mm was hunting...

[gturner]

if you are taking shots of moving targets then AI servo is your best friend.
For it to work properly you need decent lenses and camera. Test run a 70-200 L lens and see the difference. Mine is so fast and smooth you dont realise it is even happening. You then need to be in manual mode to make sure you have the correct shutter speed and exposure for the situation. Sport mode is terrible for... well... sports!

It is no good for single shots .