Auto Focus Tricks
In the last tutorial (Composition 101), I recommended against centering the subject of your pictures. Some of you may have tried de-centering and found that your subject went out of focus! Let me give you some tips that will fix that problem right up.
1.) Pick an auto-focus area
Many cameras have multiple auto-focus (AF) areas. To the right is a picture of what it looks like on different cameras (pics from http://dpreview.com). The first camera will focus on the red robot's face and the second and third cameras will focus on the center of the bird, as indicated by the illuminated focus areas.
Usually, the default setting will make the camera decide which AF areas to use. The camera can make a guess at what to focus on, but it won't always get it right.
Instead of letting the camera pick, I recommend selecting the AF area manually. When that split-second opportunity for a shot comes whizzing by, you don't want to waste time coaxing your camera to pick the right AF areas.
Moreover, my preference is to manually select the center AF area and always leave it there. Some people like to select the AF area closest to their subject, but that requires fumbling with controls for each picture, which also slows you down.
The rest of this tutorial will assume that you've manually selected the center AF area.
2.) Focus off-center subjects
Let's say we want to take a close-up picture of the water fountain above.
The hole of the water spout might make a good "eye." Let's de-center it on the right side of the picture so that it can "look" toward the left. After masterfully composing the shot, we have a beautiful picture!
Oops, the camera focused on the tree! That's because we told it to focus on whatever is at the center of the frame, which happens to be the tree. Let's try again with today's Four Steps to Better FocusTM.
Step 1: Center the part we want to be in focus.
That would be the spout. At this point, we haven't pushed the shutter button down yet.
Step 2: Press the shutter button half way.
The spout comes in focus because it's now in the center of the frame.
Step 3: Recompose.
Be sure to keep the shutter button pressed half-way.
Step 4: Press the shutter button all the way down.
Click! Now we have a well-composed picture that's also in focus!
Once you start doing this instinctively, you'll get properly focused pictures (almost) every time. Most importantly, it works fast, so you won't miss shots because you were fumbling with the controls.
3.) Use MF to tame wild auto-focus
The following tip will work best for ppl with digital SLRs which have a AF/MF (auto-focus/manual-focus) switch. If you've gotten this to work on a point-and-shoot, please leave a comment with your camera model and how you did it so that others can benefit.
If your camera or lens has a AF/MF switch, this simple tip can prevent a lot of domestic tension between you and your equipment. Proceed with steps 1-2 to autofocus to the right distance, and then let go of the shutter button (the focus should stay put) and switch your camera to MF.
Now you're free to recompose, change camera settings, and take the picture without worrying about the focus changing. Just be careful not to change the zoom because that often affects focusing. Also, make sure the distance between you and the subject doesn't change, or else you'll have to focus again.
This MF technique takes a few extra precious seconds, so only use it when you know you've got time to spare. =)
9 comments:
Hey this is a pretty cool photo tutorial blog you have here! :p
yeah, you're right. Usually AF points don't matter much as you can just recompose using the center focus.
There are some situations though where this technique isn't great because it leads to slightly out of focus subjects. (Wide angle, shallow DOF). Article here: http://www.mhohner.de/recompose.php?lang=e
In those cases, I would think the D40 is at a distinct disadvantage. :p
Neat! Now I get the point of the whole pushing-the-button-halfway thing.
I took some pictures at Blizzcon and it was pretty clear to me that I had no idea what I was doing. This stuff definitely helps.
hey this is one crazy detail post!! You must have spent a lot of time writing!!
Like you, I don't like to use full auto focusing point. I always just have the middle one selected and use half-shutter recompose method too. :)
Daniel - that's an interesting article! I've never thought of that.
He's right that it could be a bigger problem with wide angle (b/c you can recompose more dramatically), but at the same time, those shots usually have a very deep DOF to get the foreground and background all in focus.
That's some good theory to keep in mind. I'll see if it affects my shooting in real life and report back if it does. =)
I do this frequently on my dad's Canon PowerShot S2IS.
The autofocus mechanism is a bit busted, not all pictures end up weird.
I already took the VBS group pictures, they are printed, though anyone to the far left or far right end up blurry.
Should I stand back farther to fix this blurriness?
Lighting was a major limitation in the church so I couldn't stand back too far.
Bad wording in the previous post:
"The autofocus mechanism is a bit busted, not all pictures end up weird. "
Should be: "...not all pictures end up right."
vincent: yeah probably won't affect much.
are you in the bay area now? How are you liking it?
This is simply a note for Canon cameras, based on what I see in the current camera I use.
A white square is where the AF point is. When the square is green, it is set to allow you to move it. Do this by pressing the button "set" (I think...). If your shutter button is depressed slightly, a green square means it is focused to that area and a yellow square means that it is not a focused. A white square means that you did it wrong.
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