Use of AI Servo for Focusing

[Peacefield]

I plan to do some experimentation myself this weekend, but wanted to get the views of those here who are much more talented than I.

I'm about to bring my Rebel XT and 100-400 L IS lens out to a couple of races (one with historic race cars, the other GT) for the first time. I expect to do some panning shots as well as some head-ons.

Back in my film days, I was deliberately manual about everything. Manually focus on one part of track, pan with the car, and grab the shot when it enters that spot. Now, I would like to shoot sequences so I need to count on the camera's ability to continuously focus well.

I've always shot only in One Shot AF mode. With the speed of these cars, can I trust AI Servo to do the job for me? Is it typically more effective and reliable than One Shot with objects that are moving at 100+ mph? More reliable even then the old manual approach?

Any insights will be appreciated. Thanks.

[TCorzett]

Use what works for the shot you are taking. I find that AI Servo works for 98% of my shots, but I and good about giving it time to acquire the subject. There are some times when AI servo (or any auto focus for that matter) will be too slow... but that's when manual pre-focusing can be used quite effectively. The LAST thing I'd ever use with motorsports is One-Shot, as the subject is moving and One-Shot will not change focus with the subject. One of the greatest things about digital photography is that you can review your shots as you go... take some shots and see if the focus is keeping up and make adjustments as needed.

-Todd...

[PhotosGuy]

With the speed of these cars, can I trust AI Servo to do the job for me?
&
but I and good about giving it time to acquire the subject. These were taken last weekend through a hole in the fence, so NO time to aquire the subject. AI Focus, black, backlit cars & no problems:
POTN at Waterford Hills - Open Wheel Club Racing. (http://photography-on-the.net/forum/showthread.php?t=543685)

Manual exposure, too.
Need an exposure crutch? (http://photography-on-the.net/forum/showthread.php?t=89123)

[BradM]

I am always using AI Servo w/ the 30D, 40D and did previously with the XTi and Xt using the 100-400mm or the 70-200mm f/2.8 or f/4 and have'nt been disappointed. From APBA Limited Hydros running up to about 100mph to Karts, Supermoto's or Rally cars I get a very high percentage of nice images.

I have found though to get the best results I need to keep the focus point on or very close to the subject from where I initially acquire it for the servo to work the best in a series of images, particularly those that aren't moving directly at me. That is if I first acquire focus on the front fender I try to stay on that point instead of letting the focus point slide along the car to different point.

Some of the shots I have captured can be viewed at the link in my signature, good luck and have fun. I love shooting wildlife but motorsports is a very close second.

[Jim M]

I always use AI Servo with drag race cars. It seems to keep up almost all the time and that is going from a dead stop to pretty fast in a very short interval. I find that it thinks faster if you give it fewer choices, so I always use just the center focusing spot. Of the many things I hate doing to myself, perhaps the most aggravating is when I shoot a bunch of people shots at the track using One Shot and forget to switch back to AI Servo. Grrrr. Strangely enough, I only recently discovered the focus lock button and that is saving me. No longer any need to switch out of AI Servo when I'm at the track.

[Lowner]

My experience is exactly the same as BradM's. It is vital to keep the focus point nailed, so panning skills and total concentration are high on the list of requirements. Never mind the camera, If I'm not mentally focused I'm wasting my time.

And like Brad, I've got some MotoGP and F1 shots using AI Servo on the link below.

[smcclelland]

As others have pointed out it usually works best if you give AI Servo some time to lock on, I like to follow the cars into the turn if I can or track them from far away as they approach. I mapped my AF to the * button on the 40D's and let the shutter button handle the exposure and capture of the image which I find works much better for me.

Another big thing is try to focus on an area of contrast, be careful as windshields and windows can be misleading if you happen to catch a highlight. I try and get the focus point aligned on a high contrast area such as vinyl stickers or even the drivers face if the windows down (for some reason it just works for me).

Like others you can find samples of my work in my signature via flickr.