Manual vs. Autofocus

WendyMay

Well-Known Member
  • #1
As you probably already know, there are two methods for focusing your lens; manual and autofocus. With manual focus, you physically use your hand to turn the focus ring on your lens. With autofocus, your camera makes the decision where to focus. To do this, your camera makes some calculations based on distance and contrast between pixels to determine what to focus on. While using your camera's autofocus feature can be tricky at times, it can also be a huge time saver.

In today's post, I'll write about both manual focus and autofocus. I'll do a bit of explaining about each one and then I'll compare them, as to allow you to make better decisions when you're deciding which to use. None of this is particularly difficult to understand, but it will require some note taking. Because methods aren't switched between very often, it's easy to forget which feature does what.

What are Autofocus Points?

I'm sure you've seen these before. If you're looking through your viewfinder, they appear as small boxes that somehow hover on the glass. If you're looking at your live view screen, they can appear as a larger box or smaller individual boxes. On my Canon T7i, when I look through the viewfinder, I see either one small black box or multiple even smaller black boxes, depending on which mode I'm in. When I look at the larger LCD screen on the back of the camera, I see a large white box and then when I focus the lens, I see smaller green boxes inside of that white box. Again, depending on which autofocus mode I'm using.

No matter what type of camera you're using, some boxes should appear as you focus your lens. These boxes can take the shape of a diamond or a rectangle grid. That's what the Canon T7i has - a grid. When using the rear LCD screen, I can use my finger to move my focal point around anywhere I want. I can also use the arrow buttons to accomplish the same thing.

Focus Point & Plane

This is a concept you should really learn early on, as it'll help you immensely throughout your photography career. When you hear the phrase "focus point," think about the sharpest area your camera sees in your scene. So if you're taking a photo of someone's face and you focus on something in particular, that thing is the focus point. Now that you know the focus point, pretend that someone walks over to the person's face and holds up a piece of glass that, when you look at it, is flat to you, meaning, it's perpendicular, as if you're looking out a window. If the person held that piece of glass up at exactly the distance of your focus point, you'd know your focal plane. When you focus your camera, all it's really doing is making something at a specific distance sharp. So in the case of above, even though you're focusing on someone's face, anything else in the scene that's exactly the same distance away from you will be in focus as well. And as you change your focus to something else, that focal plane will change as well. It'll either move closer or farther away from you.

Many lenses also have the ability to focus on infinity. Actually, you're not focusing on a point in infinity, you're focusing on everything in the universe after a certain point. The way the lens does this is complex and it's the subject of another post, but just know that if your lens has a small window on it that shows the infinity symbol when you move your focus dial all the way in one direction, you've got that option.

When it comes to both manual and autofocus (AF), there are a few advantages and disadvantages to both. I'll cover them below.

Manual Focus

Pros: You've got total control over your focus. You can use the magnifier tool on your camera to zoom your focus in and fine tune it from there. Also, once you set your focus, it stays that way until you change it manually.

Cons: This type of focus is usable only when both the photographer and the subject are still. So it's really great for use on a tripod taking still life shots. Also, when you're trying to use manual focus while looking through the viewfinder, it's difficult to see what's actually in focus in your scene. The window is too small for that type of thing.

Autofocus

Pros: This is the easiest type of focus to use. Anybody can use it because the camera does all the work. Also, when set correctly, it's extraordinarily accurate.

Cons: Sometimes, the autofocus mechanism doesn't know what to focus on. This can occur if your scene is dark or if you've got layers of objects, where some things are closer and some farther away from the camera. While the camera can certainly choose something to focus on, it may not be the correct thing. Also, the closer you zoom into your subjects, the less accurate the focus becomes. Macro photography can be problematic for AF. This was mentioned above, but when using AF through your viewfinder, that grid of boxes remains centers on the glass. You can't move them, so if you'd like to focus on something off to the side, you're out of luck. And finally, it uses up battery power.

Two Kinds of AF Modes

This is probably the most confusing part of using your camera's autofocus, so if you can get through this, you'll be fine. If you've ever tried to focus on an object and found that once it's in focus, but the camera continued to hunt for something to focus on, this will help you out tremendously. No more frustration. Essentially, there are two different styles of autofocus on your camera. The first style allows you to focus on something, and once that thing is focused upon, the focusing will stop. You can move your camera in any direction you want, or your subject can move anywhere it wants, but if your finger is still pressed half way on that shutter button, that focus won't change at all. It'll be locked in. This type of focus is called One Shot, Single Shot, or AF-S. So if you'd like this type of focus on your camera, look for those phrases in your settings.

If you'd like your camera to continue to focus on your subject though, you can set that option as well. Think about sports games where you're taking photos of a specific player or when you're taking photos of dogs running around. It wouldn't help very much to focus once and have your camera locked that way. Continuous, AI-Servo, or AF-C continuously updates your lens's focus point, depending on what you point it at. This is super helpful for wildlife and action photography.

So there you have it. I bit of background on your camera's focal options. If you know more than I just shared, don't hesitate to share down below. I love reading what others have to say. Thanks!
 
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