How do I "focus and recompose" using spot metering?

Question

I usually use the "[auto]focus and recompose" method for taking candid photographs. In situations where there is a high degree of contrast, I would like to use spot metering to correct expose for skin-tones. However, when I do this using the focus and recompose method, exposure changes during recomposition. This does not happen using the "evaluative metering" mode.

I know I can use exposure lock to help in situation, but I am not sure how. What exact sequence of button presses on a Canon 550D do I need to use to get the result I am looking for in aperature priority mode?

Answer 1

There are two basic ways to accomplish this, and it all boils down to being able to separately control autofocus and your meter. You can meter first and then autofocus, or you can autofocus first, then meter. I've listed a few different methods, but ovens vary; adjust cooking time accordingly.

Meter, Focus, Recompose, Shoot

Method one: AE-lock on half shutter, AF-lock button.

Camera settings:

• Make sure your camera locks exposure when you half-press the shutter release.
• Set autofocus to continuous servo.
• Your AE/AF lock button should be set to AF-lock only.

When shooting:

1. Place your meter point where you want to meter. Hold the shutter release halfway down.
2. Place your autofocus point over your subject.
3. Wait until autofocus locks on.
4. Press and hold the AF-lock button.
5. Recompose
6. Fully depress the shutter release.

Method two: AE-lock button, single servo AF.

Camera settings:

• AE/AF lock button should be set to AE-lock only.
• Set autofocus to single focus (One Shot in Canon nomenclature).

When shooting:

1. Place your meter point where you want to meter.
2. Press and hold the AE-lock button. (On my camera, this will start up the meter if it has turned off after a delay)
3. Place your AF point over your subject.
4. Half-press and hold the shutter release.
5. Recompose
6. Shoot.

Focus, Meter, Recompose, Shoot

Method one: AF-On, meter on half-press.

Camera settings:

• AE/AF lock button should be set to AF-On (Or whatever Canon calls this. Basically, autofocus only happens when you're holding this button.)
• Make sure your camera locks exposure when you half-press the shutter release.

• Set autofocus to single focus (One Shot in Canon nomenclature).

  When shooting:
  1. Put your focus point over your subject.
  2. Press the AF-On button until AF locks, and continue to hold the button. (You might be able to let go of the AF-On button if your camera can be to shutter priority, as opposed to focus priority.)
  3. Put your meter point over where you want to meter.
  4. Half-press and hold the shutter release.
  5. Recompose
  6. Shoot.

Method two: Focus on half press, AE-lock.

Camera settings:

• AE/AF lock button should be set to AE-lock only.
• Set autofocus to single focus (One Shot in Canon nomenclature).
• Make sure your camera does not lock exposure when you half-press the shutter release.

When shooting:

1. Put your focus point over your subject.
2. Half-press the shutter to focus. Hold the shutter release halfway.
3. Put your meter point over your metering target.
4. Press and hold the AE lock button.
5. Recompose.
6. Shoot.

Answer 2

I have a tip regarding recompose if you do it after focus lock. As a lowlight shooter with a camera that has a more accurate center point, it is very useful to focus with the high contrast part of the subject with the center point. It is easy to get out of focus with a narrow DOF that comes with shooting wide open with an F1.4-1.8 prime.

Take a look at this geometry:

The green is the subject where you want focus on the edge (could be a face with facial features in front). The big blue circle is the thin in focus strip. the square inside is the camera, and the circle behind it is you. The blue lines circles and camera is when you focus with the center point. The yellow is when you recompose to place the face outside any focus point. (exaggerating everything to show the concept).

Notice that if you turn with your hip or front foot, you turn the camera around yourself, and move the entire focus circle. Now the object is out of focus! Aarghh.

Now, if you has a focus point and it was accurate enough in the light you have available, you could change the active focus point. But in this case not.

Take a look at this geometry:

If you instead practice your body stance to make a step around the camera as you recompose, you keep the focus circle fixed on the subject. This is the kind of epiphany where you want to bang your head because it is so obvious, but keeping it conscious in mind in the heat of battle is what it takes to change the habit of movement.

Answer 3

It sounds to me like you are pre-focusing to prepare for the perfect moment, and you want to not only pre-focus but pre-expose. If that is the case, I think you will find the following information helpful on how exactly to use exposure lock.

Aim the camera at the part of the subject or scene that’s most important to meter accurately. Press the shutter button half-way to start metering, and then press the rear AE Lock button. The asterisk will appear in the finder, so you know exposure won’t shift as you move the camera to re-compose the shot. You do need to keep pressing the shutter button half-way to keep the meter active (and locked); if you were to pull your finger totally off the shutter button, the camera would turn the meter off in about 4 to 6 seconds, and at that point you’d lose the reading you just locked-in. (Source)

Essentially you just point, press your shutter button halfway, and hit the AE Lock button. I think you will find this link very helpful and full of details on the process. I could reiterate it here, but honestly it covers the topic much more in depth then is necessary for this exercise.

Answer 4

Since I can't comment:

Could you confirm that the correct order is: 1) Place active AF point over desired focal point 2) Press shutter button half-way to autofocus, 3) Recompose to place centre-point in viewfinder over region to meter from 4) Hit AE Lock button to lock-in exposure, 5) recompose image in viewfinder to the composition for the finally photograph, 6) Fully depress shutter button to take photograph, 7) Release shutter button and AE-Lock button (in any order)

Yes, I just tried this with AE mode set to spot metering on my EOS 7D and it works. So it should be the same on the 550D.

It's worth noting that you probably don't have to do it in that order, when I fooled around I found that you can just press the AE-Lock before or after you focus. If you press it before you focus, either keep AE-lock pressed or half-press shutter release within 4 seconds (the duration is in my instruction manual).

As long as either AE-lock or halfway shutter release is pressed, your AE settings won't change. It's even possible to switch between the AE-lock button and half-pressed shutter release like this:

1. Press AE-lock once for your wanted AE settings.
2. Half-press to focus, keep half pressed and take a couple of shots.
3. While half-pressing, press AE-lock and keep pressed, then depress shutter release.
4. Half-press shutter release again to get a new focus, with unchanged AE-settings.

This seems a bit more comfortable than keeping AE-lock pressed throughout the shoot. :)

Oh, and of course what I wrote applies to One shot AF. If you use AI Servo or AI Focus the AE-lock is still active when you half-press, and focus will change automatically as per those AF modes.

Thanks for asking the question, I didn't know this!