Or rather, misconception-buster. Let me just remove a nasty misconception that crops up again, and again, and again. In people who ought to know better. Namely, focus.

Let’s start at the beginning. When we say “Focus” we mean:

• (noun): the focus distance, or
• (verb:) the action of setting the focus distance.

“The focus distance” means “the distance at which the picture is sharpest”. Not “what is my subject”, or “what else is sharp”, or “are we free of motion blur”, or anything else. It just means “at what distance from the sensor is the image sharpest”. If I set my focus distance to one meter, that means the picture is only really, really sharp at a distance of one meter. Objects that are 90cm, or 1.10 meters, away from the camera will be less sharp. Objects at 80cm, or 1.20m, less sharp still. Even when you have a great depth of field (i.e. the unsharpness away from the focus distance only sets in gradually), there is still one distance at which objects are sharpest.

CAM--//-----VVF-----VF-----F-----LF----SH----LF-----F-----VF-----VVF
 0          0.6    0.7    0.8   0.9   1.0m   1.1   1.2   1.3 metres
                                  |==========| DOF

(SH=sharp, LF= A little fuzzy, F=fuzzy, VF=Very Fuzzy, etc)

Between the two “LF” markers, the image is acceptably sharp; we call that the “depth of field”.

Select a higher “F-number” and you get greater depth of field. True, but the principle remains the same: there’s only one distance at which the image is totally sharp. If the schematic above is for a certain lens at f/4, then the same lens at f/8 might look like this:

CAM--//--------VF---------LF-----------SH-----------LF---------VF--
 0          0.6    0.7    0.8   0.9   1.0m   1.1   1.2   1.3 metres
                           |=========================| DOF

We have more depth of field (sharp range). But the focus distance is unchanged.

OK, so now we know exactly what focus is. Now to the misconception.

There are two separate, unrelated focus system settings. One has to do with HOW to autofocus (ONE STOP vs AI-SERVO, or AF-s vs AF-C). That is not what this post is about.

The other setting, the one we are talking about now, is about WHERE to autofocus.

You can use the “where to autofocus” system in two ways:

1. You choose where the camera autofocuses, or
2. The camera chooses where it autofocuses.

If you set up your camera to use one focus point, for instance the one in the centre, or one of the others, then you are choosing what the camera focuses to choose on. So it’s still autofocus, but you choose where. (That’s the mode I usually use).

If on the other hand you set up the camera to use all focus points, so that when you press down the shutter, any combination of points might light up, that means that the camera is going to choose what it autofocuses on. It looks at all the focus points, and chooses the one(s) that have the closest object behind them; it lights those points up, and it focuses on those (close-by, equidistant) objects.

Let’s have that again. If you set up the camera to use all focus points, it looks at all the focus points, and chooses the one that has the closest object behind it; it lights up that point, and it focuses on the (close-by) object behind that point. If two or three focus points have a close by object at the same distance, it will simply light up all three of those points.

So, to the misconception…

NO: using all focus points does not give you “more focus”. It does not give you greater depth of field, or anything else. It just allows the camera to choose where to focus (namely, on the closest object it sees), instead of you choosing. If you see multiple focus points, that simply means there were multiple objects at the same close-by distance.

So, misconception solved. I hope. Finally.

Next time: Should you always format your memory cards? (Hint: the answer is “yes”).

Your camera probably has a DOF preview button. Depth-of-field preview. A little button next to the lens, at the bottom somewhere. Cameras have had that button since mid way through the 20th century.

Normally, while you are preparing foe a photo, your aperture is wide open. This button allows you to momentarily close it to the set value while preparing for a photo. That way, you can see the depth of field you will get with your chosen aperture. The drawback is that the brightness also goes down during this preview, so it does not help you much.

And therefore, some of you can re-assign that button. To use it for something else. On my Canon 5D Mark 3(*) I can re-assign that button to do one of 12 different things like focus, stop focus, AE lock, various autofocus things, flash lock, and so on. Is that cool? Yes.

So on your camera, look for that button. Do you have it? If so, can you use it—or can you reassign it? If so, is there a useful function you can assign it to? If so, you have an even better camera than you thought.

That’s it for today, just a tiny tip. After shooting this all day, I am very tired:

Isn’t that a nice mom/son team? It’s so great to make beautiful photos of a mom who doesn’t have any, for herself or her son, to put on the wall. Now she does.

And I will never stop saying it: please, everyone, buy wall art rather than just having electronic files on a PC or Mac somewhere.  You will see your photos more; you will be showing them to your friends and relatives; and you won’t lose them after a crash. A win-win-win.

(*) NOTE: I shoot with a Canon 7D and a Canon 1Dx, but the latter developed a malfunction: after playing video it switches off—dead—and cannot be restarted. Canon wil take 2-3 weeks to fix it and charge me $300. So until that time? Because I shoot for a living, I had to buy a Canon 5D Mark 3 to tide me over. That’s the life of a pro: I have to have the latest and greatest, and renting one for a month is the came cost as buying and then reselling it.