AI Focus & AI Servo - What's the difference?

[barnaby_harding1]

<p>What is the difference between AI Focus and AI Servo?<br>

I switched between the two just to try, as I had been using a Canon 50mm F1.8 Mk1 and experienced the odd slip with the AF. Now I am on AI Servo, it makes a lot more noise, but seems to be focusing more efficiently - I think. I've only been shooting with dSLR for about 2 weeks, so this is all new. Bear with me!<br>

By the way, I ADORE the 50mm lens ; ) I got some lovely photos of my son's 1st birthday with it. Worth its weight in gold.<br>

Many thanks,<br>

Barnaby</p>

[craigd]

<p>AI Servo continually adjusts focus to follow a moving subject, but never actually gives you a flashing AF point to tell you that it is in focus. AI Focus will adjust focus when the subject is moving, but when it settles down, it will lock and flash the relevant AF point. So one might say that AI Focus mode switches between ordinary One Shot and AI Servo on an as-needed basis. This may, on average, use less battery power than AI Servo, and some people feel more confident when they see the AF point flash. On the other hand, some people say that AI Servo will get more shots in focus.</p>

<p>I've never used AI Focus and I very rarely use AI Servo because I don't tend to shoot continuously even for sports.</p>

[jim_j2]

<p>Barnaby,</p>

<p>Sounds like another review of your User's Manual is in order! However, to quickly answer your question.</p>

<p>AI Focus is supposed to work in a manner to let the camera choose when the subject moves and switch to AI Servo. In reality . . . AI Focus is not used very much by most from what I read here in the forums and I personally seldom to never use it.<br>

Basically the three shooting modes work as follows: (With center point focus selection)<br>

<strong>One Shot:</strong> Used mostly for static subjects, also good for focusing with the shutter button in the halfway position on the main subject, then recomposing the overall scene and maintaining the focus on the main subject.<br>

<strong>AI Focus:</strong> As indicated above . . . Lets the camera automatically switch to AI Servo if the subject within selected focus point moves.<br>

<strong>AI Servo: </strong>Constantly maintains a "predictive" focus. Most effective when the subject is moving towards you. Probably the best setting for any moving subject . . . kids, cars, people etc.</p>

<p>The AI Servo will make more noise because of the attempt to "maintain focus" while the shutter button is held in the halfway position.</p>

[barnaby_harding1]

<p>Many thanks Jim. Indeed - I must read the manual! I do find it immensely helpful getting the opinions and feedback too. I have my bedtime reading sorted for now then!<br>

Best wishes,<br>

Barnaby</p>

[tommyinca]

<p>AI Servo is a fancy marketing name for Continuously (auto) Focus. It is meant to say, unlike a digicam where the AF continuously setting is too slow to have any use. AI Servo is fast enough for a lot of cases and events (over all effectiveness still have some dependency on body and lens you purchased).</p>

<p>AI Focus = Avoid (using) If (you know how auto) Focus (work). IMHO :-)</p>

[colin carron]

<p>I have only ever used One Shot (for normal use) and AI Servo (for fast moving subjects such as birds in flight). </p>

[steven_f1]

<p>Your taking a picture of a car on a road and you set your camera to one shot. You point the camera on the car and trigger the focus. The camera will focus and as soon as it finds focus will stop. Lets assume it focuses at the front of the car and the back of the car is out of focus. You then take the shot. Bit betweeen the time tha camera focused and when you took the picture the car has moved toward you. As a result the front of the car which was the focus point is now out of focus while the back which was out of focsusis now in focus. </p>

<p>Now if we retake the shot but with the camera in AI Servo the camera would focus on the front of the car and then conterminously adjust the focus to correct for the fact that the car is moving toward you. You take the picture and because the camera was adjusting for the motion the front is in focus while the back of the car stays out of focus. </p>

<p>FI focus is a mix of the two. In AI focus the camera tries to determine if the subject is moving or if it is stationary. The camera then switches between AI Servo and One Shot as needed. </p>

 

[JDMvW]

<p>Indeed, it's not a bad idea to carry the manual with you for about the first year or so.</p>

<p>Every so often things will crop up that will mystify you if you don't have the manual along. There are a lot of non-obvious things about the camera and lens interfaces.</p>

<p>Frankly, modern camera interfaces are not particularly well-designed in terms of human-machine interaction. The human has to adapt to the machine, rather than the other way around.</p>

<p>Of course, it was even worse in the past, but there weren't so many different things to learn. I actually like shooting with an Exakta, for example. All the controls fall easily to hand -- only it's usually the WRONG hand. :)</p>

[philip_wilson]

<p>In general I avoid AI Focus as it is slower than either One shot or AI Servo for the reasons others (e.g. Tommy) have stated. In general you should be able to tell if you are shooting a moving or static subject. AI Focus is designed to be capable of either but in practice it just slows the AF down. In general I use just a single AF point in one shot mode (from my 20 years of manual focus I am in the focus in the center then re-compose school). In AI Servo I tend to use the center point but add in the AF expansion points. On the higher end models you can adjust the rate at which AI Servo responds / tracks.</p>

[daniel flather]

<p>Ignore AI Focus, problem solved.</p>

[hjoseph7]

<p>AI Focus and AI servo might work well in well controlled laboratory, but as long as I owned Canon EOS cameras, I can count on my hands the times I used these features. Tommy Lee's description is dead on.</p>

[Marvin]

<p>When I go out to shoot flying birds I have it set for AI Focus. If I come across a stationary bird, and recompose holding the shutter button halfway down, it is still OK. BUT - if I'm set for AI Servo and I want to shoot a stationary bird, and recompose holding the shutter button halfway down,, it will go out of focus. So, for me, AI Servo is not useful.</p>