Auto focus vs Single Continuous/Point focus

Question

I'm using a D600. Sometimes, having the ability to select my focus point is good. However, in certain situations, moments can be lost when you're framing or moving the focus point to the subject in the frame. This may take 0.5 or up to 2 seconds. And the perfect moment when you wanted to snap the picture, might be long gone.

Any tips on this? Thanks.

Answer 1

I have a few things I try when timing doesn't allow pre-selecting a focus point:

1. Focus and recompose
   • Using the center focus point I'll half-press the shutter and recompose to my desired composition.
2. Use a smaller aperture
   • You can use a depth of field calculator (such as this one) to ensure the subject you're photographing is in focus within the near and far limit of your focus distance.
3. Use continuous auto-focus
   • Single Point Continuous-servo AF
     • I typically don't use this because it is essentially the same as Single Point Single-servo AF. The camera only uses the initial focus point to track the subject. Focus doesn't lock and therefore you can't recompose.
   • Dynamic-area Continuous-servo AF
     • If I'm tracking a moving subject I'll use dynamic area. The camera will track the subject automatically using the focus points surrounding your initial focus point (the number of surrounding points can be set in the a6 custom setting) but you won't see the focus point change in the view finder.
   • 3D tracking Continuous-servo AF
     • I use 3D tracking if the subject is moving and I also might want to recompose after I focus. In this mode, you'll see the focus point change in the view finder as your subject, or your composition, changes. The downside to 3D tracking is it uses color to track the subject so if the background and your subject are similar colors, it has difficulty distinguishing between the two.

This page has a great explanation of the various Nikon focus modes.

Answer 2

Combining and restating Toph's answer and Matt Grum's comment: learn when to best use the (many! different!) autofocus modes of your camera, and practice with them extensively. There are many combinations of AF modes and some of them will be absolutely horrible for certain situations, while others will be horrible for other situations.

You've already identified that single-point AF is sometimes a challenge to use. Learn to recognize those scenarios and experience will help you figure out what to do next. Switching to a wide-area AF mode may be the right solution, or jumping over to manual focus may help you get the shot more easily. Learn the buttons and how to access features without taking the camera from your eye.

Answer 3

Going on the assumption you are asking about using point focus vs area focus, there isn't a perfect answer and it depends entirely on what your skill with the focus system is, the capability of the focus system and what you are shooting.

The strength of area auto focus is that it allows the camera to quickly find something to focus on without thinking about it, the weakness (and it's a doozy) is that the camera really isn't that smart and missed a couple of classes in mind reading. It doesn't know what you want to focus on, so it has to guess and often guesses poorly. You'll generally get images with SOMETHING in focus, but if there is a lot going on, there is a good chance the thing you want in focus won't be the thing it pics to focus on. If you are alert, you may notice it focusing on the wrong thing and then miss the shot while trying to get it to focus on the right thing.

Point, or the big brother zone AF narrows the scope down to a smaller portion of the image, giving you more of an ability to tell the camera where you want it to focus, but you now actually have to move the focus points to be in the area you want to focus. You can either move the points themselves (the only option if you are using a continuous focus) or you can use a one-shot type of focus that finds focus and stays there to move the camera to put the subject over the selected point, focus, then go back to your composed shot and capture the image. This is more work for the photographer and it may prevent the camera from finding something to focus on (if there is nothing to focus on under the selected area) but it also is FAR more accurate at choosing the correct thing to focus on.

As you get more experienced with it, you'll find yourself using point and zone a lot more as, overall, it is generally faster than having to fight with the AF choosing the wrong thing. It is a bit slower than when the camera gets it right the first time with area AF, but you have a consistent speed in getting the shot setup, which allows for better planning and it isn't that long when you get good.

If you happen to be shooting something that is easy for the camera to figure out the focus, or where there is lots of movement and point or zone AF isn't a possibility, then I'll move in to area AF for ease of use, but it isn't generally my preferred mode to be in. That said, I do normally put it in that mode whenever I give the camera to a non-photographer to take a picture with it since explaining point AF is a pain.