AE Lock Combined with AF Point Selection on Canon R8

[mmbrombe]

Greetings, still learning the ins and out of my (relatively) new Canon R8. I am struggling with one specific operation, where the behavior is not as expected: Using AE lock in combination with moving the autofocus point. The sequence of steps is as follows: 

(1) Point the camera to a well lit area

(2) Press AE Lock (*) to expose for the highlights

(3) Point the camera to a darker subject - exposure remains locked (as expected)

(4) Now I need to move the autofocus point. Since the R8 has no joystick, I must press the 'AF selection' button before I can move the AF point using the 4-way pad. And this is where things go south: As soon as I press the 'AF selection' button, AE exposure is unlocked, reverting back to the "darker" exposure metering. 

Am I missing a step where exposure remains locked while moving the AF point? 

Thanks for any help.

[Anonymous]

Reading this from the manual, if I read this correctly, the exposure lock is centered around the focus point, so if you move the focus point, you lose AE lock. That appears to be expected depending on the metering mode that is selected. Are you using evaluative metering?

 

[Tronhard]

What you need is back button focus, which I have used for years.  I suggest you consider the following explanation from Canon Australia explain BBF.

The issue is that focus and exposure are both assigned by default to the shutter button.  I prefer to lock focus and exposure and assign them to the back buttons.  The AF button for BBF and the * for exposure lock.  I have both focus and exposure set to spot, to get the most precise selections, given that what you want to focus on may not be the mid-tonal value the sensor want.  So, how I proceed to use them is as follows:

1. I select a mid-tone element in the picture area, and press the * to lock exposure
2. I select the element I want in focus (e.g. an eye or very specific element in an image) and TAP the AF button to lock.  If I want  I can hold down the AF Button in Servo mode to track a moving object.
3. Recompose and then shoot.

I would also consider setting the function of the button below the * button to switch between Eye tracking on/off. 

[stevet1]

mmbrombe,

I have a T8i, so I can't swear that your camera works the same way, but...

One approach might be to set your focus point first. As Trevor suggested, separate your focus from your shutter button and use back button focus. Assign your exposure lock to the * (asterisk) button.

1. Set your focus point and focus on it.

2. Using a half-press of the shutter, aim your camera at a bright point in your frame, half-press your shutter to set the exposure and lock it with the * button.

3. Exposure lock will only lock the exposure for about six seconds. It won't hold that lock. If you want to "lock and hold", I know of two buttons that will do that. One is the AF-ON button. The other one is the Depth of Field Preview button on the bottom of the camera. If you are in Servo mode, holding down the AF-ON button means that the camera will be continually focusing, which is not what you want, so the Depth of Field Preview button might work.

If you are in One-Shot, holding down the AF-ON button won't matter. It doesn't refocus until you release it and hit it again.

4. Aim your camera at your dark area and take your picture.

Steve Thomas

[mmbrombe]

Thank you all for your feedback. After some more digging, I was able to identify my particular issue: I had programmed the 4-way pad with shortcuts, which resulted in having to press the 'AF-selection' button in order to move my focus point (which somehow disengages the AE-Lock mode). Once I removed the 4-way pad shortcuts, I can easily move the focus point while AE lock is engaged. 

Thank you Steve Thomas for letting me know about the 6-second AE-Lock timer, that was (still is) driving me nuts. I don't understand why there is such a limitation - my previous (non-Canon) camera would allow a toggle between AE-Lock-ON and AE-Lock-OFF for much better control.

BBF still scares me a bit, but I'll eventually try that - one step at a time.

Thanks again,

Marcelo

[stevet1]

Marcelo,

I moved over to BBF and never looked back.

Steve Thomas

[Waddizzle]

Maybe I am misunderstand the what end result you are seeking.  I think you are over thinking and over complicating what should be a uncomplicated technique.  You are metering in one area of the scene and then locking focus elsewhere in the scene.  I would do it the other way around.

But first, I would need to know what AF Mode and Metering Mode you are trying use in order to advise you.  It seems and sounds like you are using One Shot AF and Evaluative Metering.  I would use Servo AF with Evaluative Metering, and leave both metering and focusing on the Shutter.  Here’s why.

One Shot AF locks exposure when focus is locked.  It seems to me this the central issue that you are attempting to work around.  Servo AF locks exposure when the shutter is fired, which can be used to your advantage.

The next thing to look at is how metering works.  Evaluative Metering may be the least understood of all the metering modes.  It is the factory default mode.  I must use it 100% of the time when shooting handheld.

When you have an active and locked AF point, then Evaluative Metering will bias the exposure settings to properly exposure the subject at the active and locked AF point. It is crucial that both conditions be met. When there is not active and locked AF point then metering is performed from the center of the scene, almost equivalent to Center-Weighted Average.  This last we can use to our advantage.

How would I take the shot?  I would use a Zone AF and Servo AF.  I would lock focus on the subject first using your BBF button.  While still holding the BBF button, I would recompose the shot to place my metering point in the center of the screen.  

As you recompose, AF should stay locked on your subject.  When the center of the scene is where you want it to be, then release BBF and take the shot.  Focus will be locked on your subject and metering will take place from the center of the scene.

[Tronhard]

Good to get different perspectives on this!

[Waddizzle]

Thanks, I described the steps to take incorrectly, though.  

I switched gears halfway through the write up to use BBF programmed as [AF-ON].  I normally program BBF as [AF-OFF] in my camera bodies.  I described the Shutter Button programming for the latter case, not the former.

[mmbrombe]

Thanks again for your feedback. At this point, I can get the job done using the method I'm used to from my previous camera (despite the darned 6 second AE-lock timer). I will dig further into the whole BBF scenario next. Appreciate all the help!