AI servo

[cmeptb]

Hi guys, check with you...

what AF point setting would be most effective with AI servo of most moving subjects? Eg, single AF point or auto AF.

Thanks

[Michael]

centre point is still the fastest and most accurate

[jediforce4ever]

Centre-point is the most accurate if you are able to keep the centre point on the subject to achieve focus.

For example, bird photographers that I know often use multi-point AI servo to keep the bird in focus because sometimes the creature is just too difficult to track successfully with a single point. Thats in daylight though. And most of the time the subject is pretty far away and DOF aint that shallow.

For indoors action or when the subject is near you/when you're using a thin or shallow DOF/big enough to fill at least half of the frame, single point is perhaps more useful because now you can control where your camera focuses on and sometimes you simply need to have control.

[victor]

For 1DM3...any point is the same. So usually I will compose the pics(Know where the subject should be in my frame) and then I track the subject from there. I usually track the subject for at least 1 sec before I squeeze the trigger. Did that for my F1 shots quite successful.

[cmeptb]

Thanks for your help bros.

[jediforce4ever]

Go try it out on your own when you have the time, everything boils down to personal preference.

[evershine]

Sometimes it also depends what color is your subject of focus.  If your subject wear black or dark color clothing, you may have difficulty.  It is worse if the background or backdrop is full of white/bright color banners !  The camera think white is the preferred area of focus. 

[cmeptb]

Sometimes it also depends what color is your subject of focus.  If your subject wear black or dark color clothing, you may have difficulty.  It is worse if the background or backdrop is full of white/bright color banners !  The camera think white is the preferred area of focus. 

Is this problem specific to certain models or is common to all makes & models?

[jediforce4ever]

Is this problem specific to certain models or is common to all makes & models?

Most models I would say. Its a technological fault. The chip is stupid. So when something is 'camouflaged' against the background, the AF will have difficulties tracking it. One other scenario is when things are coming or going away from you. Some camera's AF will not be able to track these movements.

[Michael]

coz autofocus detects changes in contrast mah. that's why u'll never focus properly on a plain colored, textureless wall

[hwchoy]

its not just cameras, if you look at a featureless wall, even your eyes would not focus.

[cmeptb]

Whoa, that's a lot of new & useful info (to me at least).

Thanks bros.