Friday, October 2, 2009

Woodpeckers and Auto Focus Part II: Colour Focus Tracking

Northern Flicker
It has been a slow week for me, photographically anyway, as rain and work has kept me indoors, but this evening I'm going to do some night photography, so I might do another post in the next few days covering that. As a result of the cool and somewhat wet weather I stayed home today, and in some ways that was a good thing. I was home to capture some woodpecker shoots, I love it when the subject comes to me rather than having to go looking. I was sitting doing some resurch and heard some pecking noises outside my window, which is somewhat unusual. Upon looking outside I saw no less than three Northern Flickers pecking the wooden siding of my house! My first thought was to stop them from pecking through the siding, but my second thought, and the one I acted on, was to grab my camera and get some shots. The results aren't the best, the result of shooting through my home office window, but not bad for the conditions.

Auto Focus Part II: Colour Focus Tracking

Some of the newer DSLRs from major manufactures have colour focus tracking, such as the Nikon D3000, D5000, D90 D300(s), D700, D3 and D3x. On Nikon DSLRs this is called 3D tracking. 3D tracking, from my testing is more useful when you are shooting on slow moving subjects, like a person walking towards you, or side to side. What 3D tracking does not do well is tracking fast moving subjects, like wildlife, cars and runners. To me 3D tracking effectively replaces the need to focus and recompose. For example, you could use one focus point to get the metering you want, then recompose for a more powerful shot, without losing focus. 3D tracking does better on the D300 and up, simply because those cameras have more focus points (51 points vs. 11 points on the D90 and lower), which means they are less likely to lose track of the subject between points.

When you try to using 3D tracking to focus on a fast moving subject it is very difficult for the system to keep up and it loses focus very easily. In fact most of the time, not only will the system lose focus of your subject, it will also lock onto something else which has similar colour. For fast moving subjects I've found that Dynamic Continuous AF is best, as I noted in part I. So what is the most effective way to use 3D tracking? As I noted before, slow moving, or better yet stationary subjects. Now you might be thinking, why using tracking on a stationary subject? Simple, due to the nature of 3D colour tracking, it needs to be able to latch onto a colour, and one that is steady, as even slightly different light can effect how well this feature works. The examples I've seen where it is most effective is model shoots, where the model is moving around, slowly, which allows the system to find a constant colour and stick with it. If you have a camera with this type of 3D tracking system, then give it a try and you'll quickly come to the same conclusions that I did.