AI Servo or AI Focus ~ What does this mean?

I saw another thread where this question was asked:


What do you recon for focus .. AI servo or AI focus ?

What is the difference and why would one be used more than the other?

AI Servo continually tracks the subject, re-adjusting the focus accordingly, as long as the shutter button (or 'AF-On' or * button) is pressed halfway. It's generally used for sports, motor sports, birds in flight, etc, where the subject is in constant motion.

AI Focus is supposed to predict whether or not the subject is moving or standing still, and then automatically switch between AI Servo-type mode or One Shot-type mode depending on the movement or lack thereof. It's supposed to be ideal for things like small children, who may be sitting still one moment and then scurrying around the next. It saves the photographer from having to switch modes manually.

In practice, AI Focus doesn't work very well and most people will stick with either AI Servo or One Shot. There are ways to lock focus when in AI Servo mode so another mode that is supposed to do that automatically is rather redundant.

AI focus is good for when you want shots with nothing in focus.

One shot is for stationary subject and is good if you plan to focus - recompose. Some people still use servo focus with the back button for stationary subjects, but I find one shot is more accurate.

Servo is for moving subjects.

JeffreyG wrote in post #9055530
AI focus is good for when you want shots with nothing in focus.

LMAO!!!

Well being new to this and my camera (owned for about 6 months) I have only shot in "One Shot" mode...so I guess I have some playing around to do.

Hey, I can get those in One Shot.

Yep, I just switched the camera to Servo and followed my dog around the room, I could see it continually refocusing itself.

Another question - I thought the "expert" always shot in Manual Focus - is this not the case for even the best photographer when shooting a sporting event or something of that nature?

And even another question...I assume you would always use One Shot when shooting with a Macro lens and shooting insects, etc?

LowSpark420 wrote in post #9056200
Another question - I thought the "expert" always shot in Manual Focus - is this not the case for even the best photographer when shooting a sporting event or something of that nature?

Absolutely not.

There are not too many people that use manual focus beyond certain applications where it makes a lot of sense (largely static fiddly situations like macro or for hyperfocal focusing in landscapes). The viewfinders and focus screens along with partially silvered mirrors required by autofocus make manual focussing with current cameras difficult. Modern dSLR cameras offer no focus aids whatsoever in the viewfinder.

For sure I don't know of anyone that tries to track fast sports action with manual focus. This is why people are willing to spend $4500 for a 1D body with incredible autofocus performance.

Well now I feel better about not using MF all the time!!

I guess sometimes I got the use of the "M" mode which I know doesn't control the focus but instead the aperture, ISO, shutter speed, etc mixed up as only the "real" photographer's use the M mode and MF all the time.

M mode is commonly used by experienced photographers because they understand two facts:

1. In many situations, the lighting is constant so it is desireable to lock in the correct exposure.
2. The in-camera reflective meter is easily fooled and can make the exposures all a little different.

But this is separate from manual focus.

LowSpark420 wrote in post #9056200
Another question - I thought the "expert" always shot in Manual Focus - is this not the case for even the best photographer when shooting a sporting event or something of that nature?

As JeffreyG said...

I do know one newspaper photographer who shoots hockey by pre-focusing on an area and then waiting for the action to come to him. But that's the exception rather than the rule. And he pre-focuses using the camera's AF, not by manually focusing.

In the old days, before cameras had auto-focus, manual focus was the only option. But the sports shooters would never track the action manually. Much as the newspaper photog mentioned above, they would pre-focus on a spot and wait for the action to come into the frame.

I've just started using a 6x6 medium format camera - all manual focus and metering. I assure you that even trying to shoot static portraits hand-held is quite the task, especially at the shallow depths-of-field I'm using. Trying to follow movement and motion is next to impossible. The same goes when using my manual focus Nikon FE - it's lighter and easier to handle than a medium format camera but still quite tricky to focus correctly under certain shooting conditions.

All very good information! I have not been utilizing my camera's full potential and have been learning so much about various settings, etc.

This forum rules!

The way i try to look at it

AI Servo - for moving subjects(sports).
One shot - For static shots (portraits/landscapes)
AI focus - when i dont want to know whats happening.

And as an aside - my camera is always in M because i want control of the exposure but i never use MF because the camera does a near perfect job (if i let it)