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Foundations of Photography: Lenses
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Center-point auto-focus


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Foundations of Photography: Lenses

with Ben Long

Video: Center-point auto-focus

Here's what you should already know about auto focus. When you half-press your shutter button, your camera focuses in your scene. Where it chooses to focus depends on what mode you have it in, what focus mode you have it in. By default it's going to be in a mode where it automatically selects a point to focus from amongst a selection of focus points, like we're seeing here. This particular camera has this particular number arranged in this particular pattern. In the last video you saw that you can manually choose one of these points to be sure that your camera is focused in the right spot. A lot of photographers, myself included, take a different approach to auto focus.

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Foundations of Photography: Lenses
2h 32m Beginner Feb 11, 2011

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Many of the creative options available to a photographer hinge on an in-depth understanding of lenses. In Foundations of Photography: Lenses, Ben Long shows how to choose lenses and take full advantage of their creative options. The course covers fundamental concepts that apply to any camera, such as focal length and camera position, and shows how to evaluate and shop for DSLR lenses. The second half of the course focuses on shooting techniques: controlling autofocus, working with different focal lengths, and managing distortion and flare. The course also examines various filters and contains tips on cleaning and maintaining lenses.

Topics include:
  • Understanding field of view and camera position
  • Depth of field and lens choice
  • How to choose a lens
  • Examining lens features
  • Using specialized lenses such as fisheye and tilt/shift lenses
  • Focusing techniques
  • Using filters
  • Camera maintenance
Subjects:
Photography Cameras + Gear Photography Foundations
Author:
Ben Long

Center-point auto-focus

Here's what you should already know about auto focus. When you half-press your shutter button, your camera focuses in your scene. Where it chooses to focus depends on what mode you have it in, what focus mode you have it in. By default it's going to be in a mode where it automatically selects a point to focus from amongst a selection of focus points, like we're seeing here. This particular camera has this particular number arranged in this particular pattern. In the last video you saw that you can manually choose one of these points to be sure that your camera is focused in the right spot. A lot of photographers, myself included, take a different approach to auto focus.

Rather than going with auto focus point selection or manually choosing a point, we lock our auto focus point on the center and here's why. A lot of times if you're trying to work quickly, you might be shooting and you just don't have time to stop and figure out which focus point has been selected. As you know, when you half-press the shutter button it lights up the point that it's chosen, but you've got to really be in the habit of going "Oh, good, that points on my subject." The problem is if it's not on your subject, then you have to stop and manually move and select a focus point and all that stuff we saw in the last movie.

Again, if you're trying to work quickly, it's not entirely practical. Watch what happens if I set my focus point to just the center point. Now I always know where it's going to focus. I don't have to stop and try and figure out where it is and override it. I know for sure where it's going to focus, which is great in a situation like this. I half-press my shutter button and sure enough it focused right here on this center lens. Wonderful! What if I wanted this lens in focus, or that lens back there in focus? Well, the good news is I know where the camera is going to focus.

So all I have to do is put that point on my subject. Now the problem is I've messed up my composition. But as you probably have already discovered, if you half-press the shutter button to auto focus, it stays focused at that point as long as you continue holding the shutter button down halfway. That means as long as I keep holding the button down I can re-frame my shot back to where I want it, and press the shutter button the rest of the way to take the picture. I'm not actually taking the picture here because it messes with our smart board. But the mechanism is put that center point where I want it, half-press, frame how I like, and focus.

That allows you to do things like we've done here, focusing on something to create a composition that's not entirely center focused, but it'll also get you around some other problems. Notice that if I put my center focus point on something that lacks contrast, in this case that white wall, I can press- and-hold my shutter button down and I never get a confirmation of focus. As we talked about before auto focus requires contrast. I'm just here holding it. It's not doing anything. The lens is moving around. I simply cannot focus there because there's not enough contrast.

So there will be times when maybe your subject lacks contrast, you can't get it to focus, you can put your center point on something at the same distance that has contrast in it, half press to focus, re-frame your shot, and shoot that way. One more trick that helps you in a situation like this or a lot of times in landscape shooting, anytime you're locked down on a tripod. Let's say that I know this is going to be my subject and so I've focused my shot and I've reframed and I take the shot, and I look at it and I go, "Well, the lightings are not quite right," and so I make some adjustments to lighting. Ugh, great.

Now I've got to go back in here and do this and re-frame my shot and I had it framed just perfectly. I really don't want to move it around. For times like this where once I set my focus, I know what I want it to be and I don't want it to change, now that I've got it set, I'm just going to flip my camera over to manual focus. That locks the focus. The auto focus mechanism is now out of the loop. So now I can just press the button and take my shot, confident that my camera is focused where it needs to be. I can play with the lights, do other things, press the button and I'm good. So those are a few focus tips. We're going to look at one more focus trick in the next movie for shooting moving objects.

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