Auto Focus

[iND]

Now that I have my 5D Mark III, I feel like I need to relearn autofocus to take advantage of the plethora of options.

I want to discuss the AF modes

SINGLE SHOT
AL SERVO
AL FOCUS

ok single shot has been my standard for years, I use primarily single point for focus,
and frequently use of the AE (exposure) lock feature.
The Mark III now allows us to AE lock for multiple shots. This by itself is a great upgrade for me.

AL SERVO I use when I know the subject will be moving, but the MARK III allows a setting that the shots after the first in a sequence will not fire until the AF sets accurately, this by itself will increase keepers. This feature is greatly enhanced by additional suboptions.

AL FOCUS is where I have a void in knowledge, it is suggested that it acts like single shot but will switch to AL SERVO if the subject moves unexpectedly.

So what is the downside of AL FOCUS, and i question why have I never used it.
Sounds like the it could be the best of both worlds but there must be a downside somewhere.
I suspect AL FOCUS is slow.
I also wonder about AL SERVO if the camera is moving and not the subject?

Comments appreciated.
In the mean time I plan to stay with single shot AF and add the AE lock for multiple shots of the same subject.
Focus is just so critical to what I do (weddings) I don't want the camera system to make too many choices.
Now if I was shooting sports or wildlife then AL SERVO may be used with the larger autofocus areas.
I think I will leave AF FOCUS out unless someone can give me some real advantages.

Thank you

[DavidEccleston]

Probably doesn't work for focus and recompose. I tend to ignore this mode (on T1i and 7D) as I figure I'd know if my subject is moving more than the camera would. Without more detail on how it works I can't trust it.

[neuroanatomist]

I want to discuss the AF modes

SINGLE SHOT
AL SERVO
AL FOCUS

...

AL FOCUS is where I have a void in knowledge, it is suggested that it acts like single shot but will switch to AL SERVO if the subject moves unexpectedly.

So what is the downside of AL FOCUS, and i question why have I never used it.
Sounds like the it could be the best of both worlds but there must be a downside somewhere.

You're correct - AI Focus acts as One Shot until the AF system detects subject movement, and then it switches to AI Servo.

Some of Canon's marketing writings seem to suggest that AI Focus is the best thing since sliced bread. But...on the 1-series bodies, there are only two AF modes, One Shot and AI Servo. I know what conclusion I draw from the fact that AI Focus is omitted from the Pro bodies.

[Black_Dog]

A wedding photographer colleague of mine who shoots with 5Ds (1st generation) tells me that he leaves his cameras in AI Focus when shooting events. On his advice, I gave AI Focus a shot as my default setting for a few weddings. I don't have a 5DIII, so I can't speak to precisely how your camera will work, but I got mixed results.

The pros are obvious: you don't have to manually switch modes when shooting in a quickly changing environment. At its best, the camera shoots in quick-focusing One-Shot mode when subjects are static and seamlessly switches to AI Servo if your subject begins to move. Even a slow moving bride walking toward you down the aisle with her father can walk out of the zone of focus in One-Shot mode if you are shooting with an unforgiving shallow DOF, as has happened to me when shooting wide open with an 135mm f/2.0L. So it could save your shot if the camera can change to servo mode on its own.

The downside for me is that sometimes AI Focus gets confused, especially in environments, such as a wedding reception, where there is a lot of movement in your viewfinder. It makes it hard to spot focus on your intended target and snipe a shot through a crowd. The confusion can cause lags and shots focused on the wrong subject.

AI Focus definitely has its uses, but I no longer use it as my default setting.

However, the 1DX and your 5DIII allow you to set the logic that controls the AI Servo with six preset "cases" for various subjects/environments. You might find AI Focus more useful in conjunction with presetting your servo behavior.

[iND]

I am seriously interested in single point auto-focus with a sub setting to slow the fire for the second and subsequent shots until a precise auto-focus is set.
This is in the sub menu on the Mark III, I just need to go back to the Canon learning center to figure it out.
This may decease the down the aisle frame rate but if I keep the focus point on the brides face (or her shoulder if she is wearing a veil) it will increase the in-focus keeper rate.

[HDNitehawk]

It seems one of the bodies I had used this mode, I tried it an it was not accurate enough.

I think this is what you are looking for. According to the 5D III manual you can assign a button in "custom controls" to switch between AF One Shot and AI Servo mode. It talks about this on or around page 325.

I use a similar function on my 1D IV to switch from one shot to AI, it assigns the task to a button on the superteles. I find it is very convenient.

[neuroanatomist]

According to the 5D III manual you can assign a button in "custom controls" to switch between AF One Shot and AI Servo mode.

A great feature. The 1D X has two M.Fn buttons, one of which is next to the DoF preview button and I can easily reach it with my ring finger (in landscape orientation, that is - I'm actually hitting the lower one on the portrait grip). I've got that button assigned to switch between One Shot and AI Servo, and it works very well.

There is a downside to that, though, but it applies only to the 1D X and not the 5DIII. The 1D X uses the 100K pixel metering sensor for face tracking during phase detect AF (Canon calls that iTR), but that requires auto AF point selection (61 pts) or Zone AF. If I'm in Servo mode using iTR and press the M.Fn2 button to switch to One Shot, I'm still in 61-point or Zone AF, when what I want is to be in single manual AF point selection mode.

[Busted Knuckles]

LOL - my 5diii arrived last night - playing with this morning - AF was one of the things I was playing with - so this discussion is very timely.

It is clear that you can't use "auto" to pick the focus spot in a scene that has any foreground.

I haven't tried the moving targets yet.

[iND]

I still like the single shot / single point auto focus.
It is VERY accurate in low light situations.
The 61 points have 41 non blinking cross points that are very sharp, I have tried the center as well as the peripheral points.
I do not find the autofocus screen a problem, the points are red for selection then turn black, does not seem to be an issue even in low light.


I also HIGHLY RECOMMEND to set the AF POINT DISPLAY to ENABLE to allow the AF POINT to show on playback, this will allow you to check the area that was hit for the autofocus, I find this much more reliable than trying to determine focus on the screen, this is like my focus histogram.


I am also interested in some opinion on separating the AF function from the shutter button (a feature of 1Dx and 5DIII), I am tempted to make this setting but would like some input from other users.

Thank you

[conropl]

I also HIGHLY RECOMMEND to set the AF POINT DISPLAY to ENABLE to allow the AF POINT to show on playback, this will allow you to check the area that was hit for the autofocus, I find this much more reliable than trying to determine focus on the screen, this is like my focus histogram.

Be careful... the AF Display shows which point was active, but not necessarily the spot that the camera focused on. That is, if your center point grabbed the eye of your subject, but you recomposed or moved a little after focus was acquired, then the focus point is going to be displayed on the playback wherever it was when the shot was taken... not necessarily were it focused. So if the center point was on the eye when you focused, but was over the nose when the shot was taken; then the display would show the focus point on the nose even though the actual focus was on the eye. This can be deceiving.

You probably already knew that, but there have been some that have been confused by this thinking the camera focused as displayed when in actuality they were forcused on something completely different.