Do You Know How Advanced Autofocus Systems Work?

great-blue-heron-at-iriquiose

If you know your camera, you do. The autofocus systems are often hard to understand though, so I won’t get into how they work other than to say if and when I use them. The Shoot the Light seminar helped clear up a few things I was foggy on, and I will do my best to explain it to you what I use and why.

Knowing how to use autofocus systems is essential to getting sharp images, whether you use an entry-level or professional DSLR. Even my P510 has choices.

great-egret-in-tree

Charles mentioned getting the most from auto AF systems involves changing certain parameters for different situations. He said to set up the camera to quickly access the relevant AF menus and parameters, making the necessary changes quick and painless. Granted he uses the Canon 1DX and long lenses, a very premier setup, but you can also set up Prosumer cameras in the same way.

heron-flying-3

Barring creative imagery like my soft-focus hummingbird image below, getting a sharp photo is usually my goal, especially in wildlife photography. Not having a lens long enough (80-400mm) and no ability to add a teleconverter to it, enlarging by cropping can make my images a bit soft. So getting as sharp an image as possible is important to me.

I will tell you how I set up my Nikon when shooting wildlife or landscape shots. It is all about focus. It all depends if the subject is moving fast or not.

flying-blue-heron

Focus points are those little empty squares or dots that you see when you look through the viewfinder or see on the monitor with live view. My D750 is equipped with a total of 51 AF points. My camera has many AF points to select while composing a shot and focusing on a particular area of an image.

The Nikon D750 AF system can use those different AF points for subject tracking which is useful for my bird photography. It also has cross-type sensors which are much more accurate than the vertical sensors for detecting both vertical and horizontal contrast variations. Contrast variation is a way the camera gets a sharp image.

heron-landing-1

The quality and maximum aperture of the lens are other important factors that affect AF performance as I mentioned above. Also with a long lens, your shutter speed must be at least set to the focal length of the lens., i.e.. 400mm equals  1/400 sec or greater. This helps deal with camera shake. My lens is the limiting factor on my birds in flight, most often the distance being out of range of the lens.

What Mode I Might Use

The Dynamic AF-Area Mode, rather than Single Point AF Mode works great for fast-moving subjects like birds, because it is not easy to keep focus on birds in flight. If I only want to track a small portion of the scene, I pick 9 points or if I wanted to track the entire frame, I use all 51 points to track the subject. The problem with all 51 points is it slows down focusing since so many are in play. Focusing on birds in flight can’t be slowed down.

My camera also has a 3D-Tracking system. It is used for when photographing a light-colored bird in a group of dark birds. This system will automatically focus on and track the pale bird, even if the bird moves or if I move the camera. It lets me think about composing the shot rather than worrying if my bird stays in focus.  This was a very important point made in the seminar, but he used the AE-L AE-F  button when panning his shot. I do this too many times rather than assessing my menu.

humminbird9-26-13-31

Group-area AF activates five focus points to track subjects, better for little birds. Group Area AF mode assigns 5 AF points that can be moved across the 51-point array as the subject demands, making it easier to track smaller birds.

Getting an initial focus point is important and the quicker it happens, the better the chance of capturing and tracking action. If the bird decides to fly off, you got it covered.

gull

With Group-area AF, there is no preference given to any focus point, so all 5 focus points are active at the same time. As long as one of the 5 focus points is near the bird, the camera will always focus on the bird and not the background. Panning well on the subject is important too, like above. It still tracks the gull through the tree canopy.

I use the Dynamic AF-Area mode only when photographing birds flying and typically shoot with a smaller number of focus points activated. Sometimes I use Spot AF with the AE-L button.

blue-heron

My camera settings for birds in flight.

  • Autofocus Mode: AF-C
  • AF-Area Mode: Dynamic AF-Area or Group-Area AF
  • Custom Settings >Dynamic AF Area: 9-points or 21-points
  • Custom Settings >AF-C Priority Selection: Release+Focus

green-winged-teal

For landscapes, there is nothing to track. When taking pictures of landscapes, I am careful about where to focus, so I use Single-Point AF. I use Single-Point AF also for the heron images where the bird is posing like a statue.

great-egret-in-tree-2

  • Autofocus Mode: AF-S
  • AF Area Mode: Single-point AF Area
  • Custom Settings >AF-S Priority Selection: Focus

scaup-on-landing

Focus is tough when the birds are far away, no doubt since you likely focus on the eye. While my images are not perfectly focused, it is a result of the lens, camera shake from not using a tripod, and the distance from the subject from my camera. Other words, technique sometimes plays a part. If you look at my insect photos where I am close with a zoom lens or many times use a macro lens, sharpness comes much more easily.  But, these AF Modes do help get a sharper image than I might.

This entry was posted in Birds, Nature, Photography, Photos, wildlife and tagged , , , , . Bookmark the permalink.

2 Responses to Do You Know How Advanced Autofocus Systems Work?

  1. aussiebirder says:

    Great tips and great shots Donna!

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