Control Your Autofocus Points
In conversations about multi-point autofocus systems, and on comments on this blog, a frequent question that comes up is “Why would you want all those points? I have a hard enough time with my camera picking the wrong point as it is!” Frustrated by their cameras getting things wrong too often, many of these photographers have simply set their cameras to always use the center point use and instead rely on the focus and recompose technique.
I have to admit, this response puzzled me for a while. After all, the first thing I do when I set up a camera is immediate place it into manual focus point selection mode. In fact, I don’t think I’ve let an SLR pick a focus point for me in something like a decade. In a true showing of how one expects the world to match their own viewpoint, I guess I pretty much thought everyone would select their own focal point instead of letting the camera drive this.
As happens all the time, it turns out that I was wrong in my assumption. That’s OK. I seem to learn something new every day from the conversations I have about photography and how other photographers use their cameras. And one thing is for sure, we all do things our own way.
The big problem with letting the camera choose the autofocus point is that most cameras don’t have enough working information to be able to make much more than a semi-educated guess. For example, the phase detection autofocus sensors that are used when you look through the viewfinder pass along just a few bits of information about the portion of the scene they cover. Among these bits are: 1) whether or not there is enough contrast to make a reading; 2) whether or not the area is in focus; 3) how much of a correction is needed to bring the area into focus; and 4) in which direction that correction needs to be applied. From this information, the camera also can sort out how far it is to the objects in the scene at each point.
Obviously, each camera maker uses their own proprietary algorithms to process this data. Some camera makers go beyond just the data from the autofocus sensors and will also pick up clues from matrix or evaluative exposure sensors. The fanciest of these systems can look for flesh tones—even round face looking blobs, depending on the resolution of the exposure sensor—in the exposure data to help pick a point. But, even the most complex of systems are making an educated guess based on relatively little information. Most of the time, the algorithms in the cameras I’ve played with seem to select the point that is closest to the camera and which has high contrast. Yay. That’s not a sure-fire recipe for success.
Your wetware is ever so much more powerful than the electronics in your camera when it comes to deciding what to focus on. When you look through the viewfinder, you know what you want to focus on, so why not just tell the camera yourself? Then, all it has to do is read the data from the focus point you have chosen and drive the lens to where it should be.
That said, some cameras make it easier than others to pick a focus point. Out of the box, the Nikon SLRs I’ve played with let you directly select a focus point using the control pad on the back of the camera when you are in single point and dynamic area AF mode. It’s easy enough that I was able to sort it out in a minute or two without looking at the manual while standing in a camera shop playing with a D700 and a D3. As far as other Nikon models, I’m less knowledgeable. Maybe folks can chime in through the comments to fill in more information.
On Canon SLRs, with which I have a lot more experience, you have to do a two-step dance by default. First you hold down the focus point select button and then you spin the command dials to steer the point into place. It’s easy enough to do quickly with enough practice, but until it’s second nature, it takes way more thought than it should. Luckily, with the 5D as well as later model x0D series cameras (20D, 30D, etc.), you can set a custom function to use the multi-controller joystick on the back of the camera to quickly choose your focus point. On the 5D, look into Custom Function 13. On the 40D, it's Custom Function III-3, I think. On the rest, well, you’ll have to dig into the menus a bit to sort out what’s what. I know that you can also pull this trick with the 1D Mark III using Custom Function III-9. Of course, if you’re camera isn’t listed here and you know the answer, I welcome your input in the comments as well.
The bottom line is that if you’re haven't looked into this already, you should dig into your manual and see how all of this works. Once you find that you can easily set your focus point manually, you may never let your camera do it again for you no matter how smart it thinks it is.
The photo above is of Gary Vaynerchuk speaking at Web 2.0 Expo NY 2008. The focus point on Gary’s face is simulated. No actual @garyvees were harmed in the making of this illustration.
Related Posts:
21 Comments
Nikon D60 - only has three AF points, but by default is set in a 'manual select' mode for AF points. There's three AF modes, and only the 'use closest subject' selects AF point for you automatically.
My trouble is that my muscle memory doesn't have the 'select AF point' buttons memorised...yet!
Reply to this comment
I've used both a D40 and a D200, you can use the rear command pad to choose AF points (or areas) on both of them.
The D200 has a locking collar which can be used to prevent accidental AF point choice.
Reply to this comment
I remember, back in the days of film cameras, having a Canon EOS 30. It came with this gee-whiz wonderful feature: eye control. Just look at the focus point you want, and it'll be selected! Wahey!
Unfortunately, it didn't work for me.
Wearing my glasses? Couldn't pick up what I was looking at.
Wearing my contacts? Same deal.
If I wore no correction whatsoever (annoying as hell - ever had to use a camera where you had to take your glasses off before peering through the viewfinder? It gets very old, very quickly), the dioptre adjustment only went to -2.5 ... and my eyes need -3.
Still, a nifty idea; I can't help but wonder if Canon's still working on it behind the scenes, or if they've dropped it as a neat idea that just didn't pan out. I suspect it would be a bit harder to make it work accurately with 45 AF points.
Now to look into your suggestion on my shiny new EOS 50D, and my not-quite-so-new EOS 5D.
Reply to this comment
I've been doing this for years, but always wondered how the pros did it. Especially since pro-level cameras have so many focus points and I'm used to having to cycle through them sequentially on my old Canon 300D.
Of course with the sparseness of the 300D's focus points (only 5) I still often need to rely on a slight recompose.
Reply to this comment
Er.. my camera has 7 focus points, not 5.
Reply to this comment
That's exactly how I usually set up my cameras right away. The dummy modes almost never work correctly for me. Only in certain situations will I deviate from it. I'll sometimes use 3D tracking with consistently moving subjects but normally I'll just have a single point surrounded by 9 or more helper points. A far better option than using the center point and recomposing which leads to focus parallax as you discussed earlier and is a major problem especially with longer lenses and large apertures. Good posts!
Reply to this comment
Maybe people who routinely rely on the camera to choose a focus point are also using the stock, relatively slow lens that came with their camera? If your lens won't go faster than f5 and you aren't making large prints, you might not need to be picky about the exact focus point chosen in the viewfinder.
Reply to this comment
On the Nikon side, the new 3D colour tracking AF system is impressive. While it's not perfect, when it does work it's sort of magical. For your kind of work, the 3D mode isn't useful. But if you're photographing a football game, hockey, basketball where your subject is moving quickly and other players are moving in and out of the way, then it's probably more powerful than wetware.
The D3/D700/D300 share the same AF/metering system. It's fastest on the D3, slowest on the D300. You set a switch to specify the type of AF you want, then use the arrow pad to control the point (assuming you've not chosen the magic 3D setting where it does everything on its own).
For portait work, the D300 is best because the 51 AF points cover most of the sensor. It's easy to set one point on the eye. With the D3/D700, not to easy to focus just on the eyes.
On the D200/Fuji S5, you have more options with the switch, the system is slower and not as precise as the above.
Olympus's E-3 has a very fast AF system. It's predictive AF system isn't as sophisticated as Nikon's current high-end approach. I'd put it just below Canon's 1D system. To change AF points, you press the AF point button, the AF points light up, and you use the arrow pad to pick your point. I didn't like the approach in real life - I prefer the Nikon/Pentax system where, unless you lock the AF point, using the arrow pad immediately affects AF. But the 9 main AF points are all cross-type and all v accurate.
Pentax, in terms of camera body usability, have my favourite approach on the K20D/K10D. You roll a wheel to select predictive AF, user-specified, or lock it to the centre point. In user mode, you use the arrow pad like on Nikon and Olympus. The nine main AF are all cross-type and all very accurate. Overall the AF system is slow, while fine in good light, dog slow in poor light.
If I could design a camera body, I'd start with the K20D and add in the guts and sophistication from Canon/Nikon's high-end systems.
Reply to this comment
The Olympus E-3 has 11 points, and it is relatively easy to shuffle through them to the one you want by pressing the focus point button and then wheeling the two control dials (front for horizontal, back for vertical), though this can also be reconfigured to move through them in a spiral motion, etc.
I have never understood the purpose of the widespread default behaviour of "let the camera randomly choose what to focus on."
Reply to this comment
I've never used a pro-level camera, so maybe this has an obvious answer: how does this technique work for less than static subjects (sports, wildlife, etc.?) Surely it isn't possible to select one of 45 focus points that quickly. Or is it?
Reply to this comment
Stuart, I had (still have, actually) an EOS 3 that has Eye Control. I was one of the lucky ones for which it worked out quite well indeed. From what I can gather from the various vague comments on the subject, Canon isn’t moving forward with this stuff at all anymore. It’s too bad, really. Though, I can see the problem with trying to market a feature that only works with a fraction of your customer base and leaves the rest frustrated.
Reply to this comment
Luke, yes indeed. The servo stuff on Canon is always impressive when it works and I look forward to playing more with the color tracking 3D AF on the Nikon. On Canon, when I use servo mode, I still pick the starting point myself typically. And when I played with the Nikon 3D tracking at the store, I did the same thing. Picked a point, focused on it, and then starting moving the camera and watching the point track. I have to say, being able to watch the tracking point on the Nikon system is really nice compared with not having the feedback on the Canon systems.
Reply to this comment
Great topic Duncan. I don’t understand why camera mfgs. don’t push the focus points out into the corners. Of course there are technical issues the further from the center you move; I don’t care, give me the option to pick a point that may only work marginally and I’ll deal with it. Just get me close and I’ll override with the focus ring.
I shoot a D200 which only has a cross-type focus point in the center and I still rarely use the center point, even when I’m tracking. There are a myriad of focus point options on the Nikon (they actually cut back on newer models) but over time I have settled into pushing a single focus point all over the viewfinder.
Focusing anywhere but the center of the frame is what held me from making the AF jump (that and a lack of funds), until Canon introduced the A2e which had the eye focus mentioned above. For me, it was dead nuts accurate under all conditions; the type of technology that gives you chills, a game changer. Apparently (and sadly) it didn’t perform as well for the general population and hasn’t been carried over to the digis.
For me the dream AF system would be full frame coverage with continuous eye tracking. My eyes aren’t getting any better.
Peter: on cameras w/ dozens of focus points, manually selection moves within the “traditional” 9 or 11 point pattern.
Reply to this comment
Peter, I'm pretty quick with my 1D Mark III, but part of that is practice probably. I do choose a general area of the frame to start with based on the composition, sometimes even as I’m lifting the camera up to my eye. Then I fine tune as I go. When things change suddenly, it doesn't take long at all to shuffle that point across.
Reply to this comment
On a general note, thanks to everyone for the Nikon comments, as well as the supportive comments in general. I so appreciate your contributions here. I’m also super happy that picking up the blog schedule seems to have been a good thing to do.
Reply to this comment
Ben, you're right. The E-3 has 11 cross-type sensors. I remembered it as 9 cross-type and the two outermost sensors as being simple points.
The Pentax K20D has 11 AF points as well, but the two outermost ones aren't cross-type points. In low light, I'd trust just the centre point.
On the D3/D700/D300, of the 51 AF points, just 15 are cross-type.
Buck, apparently there are technical reasons why the AF points don't reach out to the edges. Thom Hogan mentioned something recently but he didn't go into any more detail than that.
The upcoming micro-four-thirds camera from Panasonic, the G1, will let you set the AF point anywhere in the viewfinder/LCD (I assume like the Canon G9). But it uses contrast-detection AF, not a phase-detection AF system. It's supposed to be dSLR-speed, though I doubt 1D/D3 speeds. My guess is D60/Rebel speeds. And because it's contrast-detection based, I'd not expect AF to keep up in low light.
Reply to this comment
I went up very steeply, starting with D70, then a D200 and now a D3. I have to say when I shoot people and get as close as a heads and shoulders photo, relying on the D3's AF to pick the right focus point is much better than I am (people move their heads about faster as I am with resetting the focus point). With the D200, I mostly selected the focus points manually, not with the D3 anymore if the shot is time-critical.
Reply to this comment
Thank you for such a wonderful series on topics that are simple to some, and mystifying to others.
Here's something I've always wondered, though. Let's say I'm shooting a soccer player. He's moving, so I turn on AF Servo mode (on a Canon XT/350D). There's a player in front of him, so I've got the center point selected manually and I focus on him, and then let him run across the frame. Will the camera use all the points to track him, or only the center one? (or is this just wishful thinking with a Rebel?)
Reply to this comment
enjoyable read Duncan, thanks. FWIW, the D80 works the same way with the back control pad. In fact, I'm going to start experimenting with it more now.
One question--how does this change for you when shooting a fast moving subject?
Reply to this comment
I've had my 20D setup like this for a while, but never made the connection to do this on every shot. I just played around with it and it isn't that hard, the directional pad is right under my thumb.
Thanks for the info on this!
Reply to this comment
Exactly. I know I used to use the centre focus point for most of my images, until it became a limiation.
For example a subject say, child on a bike in AI Servo mode. If the centre point was used and focus on the eyes then there would be blank sky above as you cannot recompose.
Not to mention attempting to track a bird in the sky with a long focal length lens. Straight onto all focus point activated.
Thinking and then using those focus points as the situation warrants is a boon.
Reply to this comment
Leave a comment