Auto Focus (AF) Modes 

This subject will be short but sweet and address a very common question.  Which AF modes to choose and for what subjects.  

I’m not going to detail the actual names of the modes among camera manufacturers, nor will I cover each model in detail in regards to which modes it has.  What I will do is use generic easy to apply mode names and talk about their appropriate use.  You can apply this discussion to your own camera model.

  

Static Mode 

The first would be “Static mode”, sometimes called “One Shot” or something similar.  This mode is made for static subjects.  Once you focus on the subject, as long as you hold the shutter release halfway down, the focus will remain the same.  Static mode is useful for portraits of still subjects, landscapes, or anything that doesn’t move.

Static mode is hands down the most accurate AF mode available.  It allows you to choose an AF point, place that point on your intended point of focus (such as the closest eye on a living subject, human or animal), and achieve the most accurate focus possible.

Once you understand that static mode (One shot) won’t “refocus” unless you release the shutter button and start over, then you can develop techniques for it’s use on slow moving subjects or subjects that strike pose after pose.  I use static mode almost all the time for people portraits, slow moving model shoots, animals at rest, cars, or anything that doesn’t move, OR moves slow enough where I have time to refocus on the move.


Dynamic Mode  

This is sometimes called “Continuous Mode.”  The camera continuously tracks the subjects movements and refocuses as necessary.   This can be very accurate, but by nature is less accurate than the static mode.  Dynamic mode is also highly dependent on technique.  Good technique is vital to the success of this mode. 

Anything that moves faster than you can refocus by letting up and pressing the shutter release button, is considered dynamic and Dynamic Mode (Continuous Mode) is the mode to use.  Sports, moving vehicles, fast moving people, flying birds, running animals, children at play, all would benefit from using the Dynamic Mode. 

I’m not going to go into the technique(s) used in Dynamic mode.  Each type of subject requires its own technique and tons of practice if you want to achieve a decent level of competency.  Fast moving photojournalism requires a certain technique, the fast moving parts of a wedding, auto racing, birding, every use requires a slightly different technique and the use of extra modes some lenses provide like memory settings.  I’ll cover some techniques in future columns as they apply.  And of course I cover these during workshops.   The proper techniques used in Dynamic Mode make a huge difference.  Huge. 

 

Anything Goes Mode 

You won’t find this mode on professional series bodies like the Canon 1d’s, but you’ll find them on the prosumer DSLRs like the 5d Mark II, 40/50d, and the Rebel series as well as their Nikon counterparts. 

What this mode does is it starts you off in Static Mode.  However, if during the capture process, if your subject moves for any reason, it automatically changes into Dynamic Mode and tracks the change thereby achieving proper focus.  Sounds ideal?  I think so.  Static subjects start moving all the time and this accounts for many lost opportunities.  I have yet to fully check out this system so I can’t comment on it’s effectiveness, but if we assume it works great then why not only have this mode available? 

And why don’t pro level bodies have this mode?  I’d hazard a guess that pro level bodies don’t need it.  On a pro level body the Dynamic Mode (continuous mode) is so responsive and fast, that it effectively achieves the same thing as Anything Goes Mode. 

If your camera has this mode by all means give it a try and see how it works for you. 

 

Beyond Modes 

To truly master focus you need to develop skills beyond the standard AF modes.  Canon L series lenses and Nikon AF-S lenses have a feature vital to professionals called “full time manual focus.”  This means that at any time during the AF process you can grab the focus ring and assume instant control over the camera. 

You’ve heard me refer to “pushing” or “pulling” focus?  This is what I did during the darkness of Loy Krathong when the subjects were too dark to achieve AF on their eyes/faces.  I let the AF key on the flame of the candles, focus, and then I’d pull/push the focus manually from there to get the best possible focus.  This enabled me to achieve focus 10x faster than just straight manual focus.

 

On the picture above the lady is behind thick iron bars.  The AF kept locking on the bars and not her face.  At the wider aperture I was using the DOF was not great enough to have both the bars and her face in focus.  I simply let the AF lock on the bars just inches from her face, and then grabbing the focus ring I pushed the focus out to her face.  Perfect focus


On the picture above the lady is behind thick iron bars.  The AF kept locking on the bars and not her face.  At the wider aperture I was using the DOF was not great enough to have both the bars and her face in focus.  I simply let the AF lock on the bars just inches from her face, and then grabbing the focus ring I pushed the focus out to her face.  Perfect focus! 

Depending on the speed of events you can’t just sit there and perfectly manually focus on their face, especially if it’s too dark to clearly see them.  So you develop “techniques” that ensure the highest rate of success and speed combined.

I always use Brightscreen’s excellent Pro Split Level Diagonal focusing screen with 8x10 vertical crop lines.  These are expensive but the huge focusing prism allows fast adjustment when I need it for fast moving subjects, and very careful precision alignment for static subjects.  

I almost always manual focus on static portraits, landscapes, static subjects, and when using manual focus only lenses like Canon’s excellent Tilt-Shift (TSE) lenses.  My TSE-90 is more sharp manually focused than all by 1-2 very expensive AF lenses I own. 

Technique.  Knowing which AF mode to use, on what to use it, and when/how to deviate from these modes.  This is the key to critical focus along with proper bracing/support, mirror lockup when appropriate, using an external shutter release when appropriate, the ideal aperture for your lens, and of course a high quality lens.  Critical focus is difficult to achieve, but it produces dividends that will keep paying off in the future.