Manual focus? Six reasons.

Should you ever focus manually? When?

Well, yes. Indeed there are circumstances where manual focus (setting lens or camera switch to manual focus, and turning the focus ring yourself) is the way to go.

And here’s a few of those circumstances. I can think of six right away:

  1. Macro. When shooting macro, for instance when shooting flowers, bugs, food or jewelry, use live view and zoom in electronically if you can, then use manual focus.
  2. You are using a Nikon D40/60/3000/5000 and a fast 50mm lens. Those lenses do not autofocus on those low-end Nikon cameras, so you have to do it by hand.
  3. It is night. Your camera cannot focus well in the dark.
  4. When shooting through glass, like on an airplane.
  5. The subject has low contrast. Ditto – you may have to do it by hand.
  6. When the subject is unpredictable in time but not in space – like fireworks. Or sports, when you know where the action will be. Pre-focus there manually!

Tip: Do not confuse manual focus with “using one focus point”. When using autofocus, you should always (or virtually always) use one focus point. When the camera chooses it will choose what you do not want to see sharp.

Homework: go take ten pictures right now where you focus manually. You;ll see how easy it is, and how consistent once you get it right.

Autofocus and how it works: the modes

A regular reader asks (and I take questions, you know that, right)?:

Can you possibly do a short blog entry on the focusing modes offered by Canon? You know the ONE SHOT – AI SERVO – AI FOCUS buttons?

Certainly!

These “focus modes” are not about where the camera focuses (the focus point selection is about that: select one point for accurate control). Instead, these modes are about how the camera focuses. There are two main modes and an in-between hybrid mode:

  1. One shot (Nikon calls this “AF-S”)
  2. AI Servo (Nikon calls this “AF-C”)
  3. AI Focus, where the camera tries to guess which of the above two you want.

“One Shot”/AF-S means: when you press the button, the selected focus point tries to achieve focus. Once it does, a few things happen, all at the same time:

  1. The camera beeps
  2. A green dot lights up steadily
  3. The focus locks, and until you remove your finger, it stays locked at the selected focus distance.

This One Shot/AF-S mode works well in most cases. But what if the subject you are shooting is moving rapidly towards you, or away from you? Then every picture will be blurred, because by the time you press, the object is no longer where you locked the focus.

So for those situations you have AI Servo/AF-C (AI Servo means “Artificial Intelligence Servo motor control”, while AF-C means “Autofocus -continuous”). The focus never locks, and the camera keeps buzzing away as the focus motor keeps turning and adjusting. Better, it even predicts where the object will be when the shutter opens (that is the “artificial intelligence” part). So you can try to use this mode when shooting “sports, birds, and kids”.  Not every shot will work out, but at least some will.

Finally, the hybrid mode (AI Focus) tries to guess which one of the two modes above you really want, and then switches to that. I am not a great fan, and expensive cameras like my 1-series models do not have this mode. I think you should probably decide whether you are shooting mainly stationary subjects (then choose One Shot), or moving objects (then select AI Servo).

Reader question: Focus

RG, a regular reader, asks:

I just still struggle getting my subject in sharp focus.

I shoot in Auto Focus mode on my Canon Rebel XSi (usually in Program Mode). I manually select my “red” indicator and try my best to focus on what I want sharp. But what do I focus on when my subject doesn’t fall neatly on one of the AF points? I tried to pick the nearest one to my subject — sometimes it comes in focus, sometimes not.

If I am taking a portrait of two people’s faces and they are cheek-to-cheek — sometimes one face is sharp while the other is not! Annoying! In that case, where do I place the red mark on?

Great questions. And the answer comes in three parts: motion blur, focus blur, and depth of field.

Let me start by saying “it’s not just you”. Everyone struggles with focus. I do, too.

  1. One important reason is that we are more critical today than in the past – we zoom in. Take your blurry picture and print it at 4×6 and it will probably look just great!
  2. We take many more pictures in low light, where we would not have tried in the past.
  3. We have two distinct kinds of blur: focus blur and motion blur. They are easy to confuse.

So then let’s start with motion blur. Your first picture’s unsharpness was mainly due to motion blur: it’s a shaky picture. It was taken at 1/30th at f/1.8 on a 50mm lens. The 50mm lens works like an 80mm lens on your Canon Digital Rebel. To get sharp pictures, a rough rule of thumb is: “stay at one divided by the ‘real’ lens length – preferably twice that”. So you should be at 1/80th second, maybe even 1/160th second, when handheld. 1/30th is  pushing it. No problem trying, but steady the camera, lock it onto your face, don’t breathe, and take the picture ten times, then pick the sharpest one. Or… use a tripod. Or go up to a higher ISO value to increase the shutter speed.

Now to focus blur. The second picture is blurred mainly due to focus: the closer part of the girl’s clothing is sharp while her face is not. That could also be motion (her motion this time – not yours; she is turning her head) but it is to a large extent it is focus.

You are focusing with one focus point: this is always the way to do it! But what if there is no focus point where your subject is?

How, in other words, do you take a picture like this?

Selective focus

Focus-recompose-shoot

Actually that is quite simple and I want you to reproduce that picture now. Use a technique called “focus – recompose – shoot”:

  1. Select a focus point near the subject;
  2. Aim that focus point at the subject;
  3. Focus by pressing half way down. Wait for the beep that indicates “in focus”. A green dot appears too, at the same time.
  4. Hold your finger there – do NOT let go! But also do not push all the way down.
  5. Now recompose the picture (while still holding your finger down).
  6. Now finally push down to take the picture

Hah – your hand is now still sharp, since pushing half way and holding your finger there locked the focus distance, until you either let go or push down.

Finally to depth of field. What if you want more than one thing to be sharp?

  1. Use Aperture mode (Av), and select a not-too-small Av Number. f/1.8 will give you very very shallow, selective, depth of field. f/5.6 gives you much more sharpness (but slower speed); f/16 and much of your picture is sharp (but now even longer shutter speed so you must use a tripod and tell people to not move).
  2. Aim at a point in the middle, So if you have to shoot three rows of hockey kids, focus on a kid in the middle.

So now you know how to avoid blur, how to focus accurately, and how to get enough in focus.

All you need to do know – and you know what I am going to say: practice!

Focus where you want.

…where you want, I mean. Not where the camera wants. So as a tip for beginners and reminder for others, a few words about how to focus.

When you look through your viewfinder, you see focus areas, also known as focus points. Depending on your camera there are three, five, seven, nine, or even 11 of 45 of them.

When you press the shutter button half way, the camera indicates one or more of these by flashing them; then it beeps. As long as you hold your finger on the shutter button, these selected focus points stay active. Meaning that when you press down, that’s where the camera will focus.

How does it select which points to use?

It looks at all the focus points, and selects those that are on the closest subject. That’s how. So you’ll get this:

And therein lies the problem. What if you want not my hands in focus, but my face? Or what if you are shooting a relative in the forest and you keep getting that closest branch in focus rather than the relative?

That’s why you can disable this automatic selection of focus points.  And most people do most of the time. Ask a pro how many focus points he or she is using and the answer is almost always “one”.

Then you can:

  1. Select a suitable focus point
  2. Aim that one point at your subject
  3. Press half way down until your focus points locks and the camera beeps
  4. Hold your finger on the shutter, do not let go
  5. Recompose if necessary
  6. Press down and take the picture.

Q: In a portrait, what really needs to be sharp?

A: The subject’s closest eye. The rest is optional.

My student yesterday in a Henry’s Canon 7D class, taken with the 7D with 35mm f/1.4 lens using available light and, um, a TV:

Advanced users, did you know the following:

  • Focus selection is done in areas that are actually wider than the indicated focus spots.
  • The centre spot is the most sensitive.
  • The faster your lens (low F-number), the better it works.
  • Focus squares detect lines. The centre spot is sensitive to horizontal and vertical lines. Others can usually detect only horizontal or only vertical lines!

Well, now you do.

And if you are new to this, here is your assignment: reproduce this photo. Hand sharp in the very corner of your photo.

(Use aperture mode with a low “F-number”, or use program mode and get close).