Focus Limit Switch #135

Focus Limit Switch #135

A focus limit switch is the third switch on your long lens or macro lens. On most lenses you will have at least two switches. The autofocus on and off switch and the stabilization on and off switch. But if you have a long lens or a macro lens, you may have a third switch. This is your focus distance limit switch. Boy, that's a mouthful! The switch will have the word FULL on one side and then a number, the letter M, dash, the infinity symbol, which is a figure 8. It may also have a third option in between with a number, the letter M, dash number, and letter M. So what is this switch and what do you do with it? This switch sets a limit on the distance your camera will focus. For instance, if it says 8M dash infinity, it means that you will only be able to focus on objects that are 8 meters away to infinity. You will not be able to focus on anything closer than that. But why would you want to limit the functionality of your lens like that? Let's say you're shooting gazelles in the distance. By shortening the focusing range, the camera will disregard anything that is closer than eight meters, so that if someone or something comes between you and the gazelle, your camera will not try to refocus there. Which means you'll be able to keep your focus on the gazelle. Also, by shortening the focusing range and disregarding close objects, it means that you'll be able to focus on things in the distance faster. This is definitely a great option. On the complete opposite spectrum, we see on macro lenses the ability to focus on things that are very close to the lens. Again, this will speed up your focusing.

Let's say you're photographing a small flower and you're very close to it, so you'll fill up the frame. You're also using a small focus area because you just want that one flower in focus. But then a slight breeze comes by and blows the flower out of the focus area. If you did not limit your focus, the camera will now try to focus on the ground, which is a few feet away. Then the flower comes back in the frame and the camera has to try to refocus on the flower again. You're starting to see the problem, right?

If you had set a limit on the focus distance to only things that are under two feet from the lens, then the camera would not have tried to focus on the ground and have to refocus back on the flower when it came back into the focus area, making your focus much, much faster. We've all had a situation where the lens is going bzzz, bzzz, bzzz, back and forth trying to find focus, from near to far, from near to far, right? By setting your focus distance limit, you can help reduce this problem.

In the next episode, I'm going to talk about image stabilization.