How to meter from one area and focus on another

So many of my readers are getting into employing back button focusing more since I started talking about it here on this guest post for RTS. But then I introduced metering modes in my Backlighting 101 series and now, everyone’s wondering ‘how do I tell the camera what point to meter from AND where to focus at the same time?’

Incase you’re already feeling lost, let me quickly explain the 4 things you need to understand about controlling these elements in your photography. Now, bear in mind I’m a Canon girl and these terms are as I know them for Canon models but I’m sure the concepts remain the same for other cameras.

Metering :: When I say ‘tell the camera where to meter from’, what I mean is when you’re in one of the semi-manual modes like AV, you set your aperture and other settings which you’re able to control and then select a metering mode which is appropriate for your scene which will help the camera choose the right shutter speed. For example, with regards to backlit photography which we’ve been talking about recently, using ‘partial metering’ means you can make sure the camera is setting the ISO and shutter speed to properly expose the scene for the subject and not the super bright backlit background. If you’re shooting in completely manual mode, you can still set a metering mode but instead of changing any settings for you when you press the shutter halfway, the camera will just show you in the viewfinder screen exposure level indicator if you’re on target with your settings for the type of metering you’ve chosen. That part of your screen looks like this:

When the moving target is in the middle of the line {where the 0 is} then that’s the camera telling you that it thinks your settings are right for the correct exposure. So if you choose a different metering mode in manual, no setting will change, only the reading on that indicator will change. If you use a metering mode in a semi-manual mode like AV, then some of the settings will actually change when you press the shutter halfway.

Focus Points :: Another thing you might be toying with now is your focus points. I always manually select my focus point by toggling the little red square in my viewfinder. More on that, using the Canon 7D as an example, here.





Back Button Focusing :: Like I said in the beginning of this post, I recently introduced my readers to BBF {back button focusing} over on Rock the Shot. No need for me to be redundant and explain that all here again. Click here to read that super plain english explanation for why you might want to use it and how to dive in.



AE Lock :: This is something new which I’ve never explained here on the blog before. The AE lock button locks your exposure settings. It freezes the camera’s settings so that if you move your camera slightly or are following a moving subject, the settings will remain the same.




How to focus in one area and meter from another

So all that leads up to the big question I’m getting from readers: ‘how do I choose one spot to expose and another to focus on?’ You’ll find that since the camera uses the red focus point in your viewfinder for both the meter/exposure reading and the focusing, this can present a problem.

It’s all about the AE lock button. What you do is press the shutter halfway to meter the scene and grab the setting you want the camera to use. Then, press the AE lock button to lock the settings and you’re free to then move your camera without any of the settings changing. You’ll see the * lit up in your viewfinder screen until after you take the shot. However, should you then press the button to toggle to a different focus point, the AE settings will no longer be frozen and you’ll have to take another reading for your meter and re-lock it before proceeding. The way you can combat this problem is to use the center focus point, press the shutter halfway to take your exposure reading, press the AE lock button to freeze those settings and then, instead of moving your focus point, hold the back button to focus where you want {still using the center focus point} and then recompose and hit the shutter.

Please feel free to discuss the scenarios where you find this method useful below I’d love to know how everyone deals with this in their own ways.

Other Ways

Other ways to do it which have come in since this post first went live:

Change the custom setting of the shutter release to be the AE lock when the shutter button is half-pressed so you can keep your forefinger on that and your thumb on the back button ready to focus. First, choose which focus point you want to use, then point that where you want to meter and half press the shutter. Then recompose to get the focus square to your desired focus point and press the back button. Then fully press the shutter to take the image.

Pin It
  • Jay

    Hey Elizabeth – great post!  I have a confession: I’ve never used AE lock.  That’s in large part due to always shooting in Manual Mode where AE lock doesn’t work.  It’s just how I started doing it from Day One and never really take many photos without a tripod, so I have the time to take my time in M.  I’ll have to give this a try though soon on my Canon.  Appreciate it!


  • I, too, started using the back focus button recently and find it far easier. I found it too difficult to use the back focus button and the AE lock button, as I couldn’t coordinate this without taking my eye away from the viewfinder, so I have changed the custom setting of the shutter release to be the AE lock when half pressed, so I keep my forefinger on that and my thumb on the back button ready to focus. First I choose which focus point I want to use, then point that at where I want to meter and half press the shutter. I then recompose to get the focus square at my desired focus point and press the back button. Then I fully press the shutter to take the image. After a few times it becomes second nature.

  • Anonymous

    Oh that’s an excellent alternative! I’m going to add that to the post for those who don’t follow the comments. 

  • Diane

    Thanks Elizabeth. I should add, I use a 40D, but I presume the custom function to do this is available in other models. That function is C.Fn IV-1 Shutter Button/AF-ON button, option 3.

  • Sandy Young

    Elizabeth, thanks for this post!  I shoot in Manual all the time, and have my AE Lock button set up as my BBF, and it works well for me.  You threw me with one of your points, though.  I thought that the middle focus point was the ONLY point that Canons metered from.  And that it doesn’t switch when you toggle to other focus points.   The way that I understood your post is that Canons metering points could change when you toggle your focus points?

  • Diane

    Sandy, in a book I have that goes into more detail than the camera manual (Canon EOS 4oD Digital Field Guide), it gives information on AE Lock behaviour in relation to metering and AF point selection.

    When you are set to manual AF point selection, and in Partial, Spot or Center Weighted metering modes, the AE Lock is set at the center AF point (regardless of the focus point you have selected for focusing).

    Again in manual AF point selection, but with Evaluative metering mode, the AE Lock is at the selected AF point.

    In Automatic AF point selection, with Evaluative metering, the AE lock is set at the AF point that achieves focus.

    If you switch the lens to manual focus, with Evaluative metering, AE Lock is set at the center AF point.

  • Sandy Young

    Thanks very much! 

  • I spent hours trying to figure out what button on my 7D was the BBF.  From your post I found you hold down the AF-ON and click the shutter button. Talk about an ah-ha moment!!  But I’m not sure BBF is really for me since you have to HOLD it down.  I feel it would work better for me if you could push that button and it would stay that way, like if you pushed it on a tripod and then went in front of the camera to get a shot.  I guess I’m just so used to holding down the shutter, and I’ve learned how to get in front of the camera with my remote.  Thanks for the info, just found your blog.  It’s great!

  • Jeffrey

    Hello Elizabeth! I have been endlessly googling in an attempt to find anything even remotely useful. Sure I found some pretty good youtube videos and a few decent blogs here and there, but I just wanted to thank you so very much for writing in the way that you do; and in being thorough! I recently bought a beautiful new 7D and am finally getting the help I’ve been hoping for. I do think I’ll continue locking in the AE (usually with spot) then AF with the half shutter press and click. It just works for me. But there are so many possibilities with this camera and I’m sure I’ll try it all right along with you! 

  • Vannareed

    Elizabeth, I just came across your blog and fell in love, I’m definitely here to say!! 8) I do have a quick question, as I’m new to BB focusing… I have a canon 5d mark II and to BB focus, it’s actually the other way around from how you put it, I use the AF-ON button to BB and I’m unable to to press the shutter half way down to take the exposure reading ….???? Please help!! Which makes me think that i haven’t even been getting a reading. Thanks again!!

  • Vannareed

    That was suppose to be here to stay**!

  • Kim

    Great post, all very well explained!

  • Jen

    I use BBF, and I don’t hold the button down. I just push the button and it locks the focus, so I can jump into the shot if I want to. I like it best because if something moves between me and my subject (like people walking past or the wind blowing tree branches), I don’t have to worry that my camera is going to try to focus on those things; it stays focused on the right spot, so I just have to wait for a clear shot and click away.

  • Seth

    My god, I just now learned how to do this! Thank you! Plain English…

  • KNK

    Hi Diane, I’m struggling with BBF’ing and metering with my Canon 60D. I had thought with Canon’s that only the center point can be used for metering. Is that not correct? Maybe I misunderstood your process, but if you use something other than the center focus to focus (and meter), does it actual meter correctly? Thank you.

  • KNK

    Ok I read a bit more. If in evaluative metering mode, the exposure will be locked but it’s not only using that focus point, it’s using the entire scene with that focus point weighted more. I would love it if this would work in spot metering, but Canon’s don’t do that. :(

  • Rob Leacock

    Hi, the way I do it is to Change the custom setting of the shutter release to be the AE lock when the shutter button is half-pressed, and then have the focus on autofocus continuous. So I point at the area I want to meter from, half press the shutter button, then (keeping the shutter half pressed), move to point at the intended focus point and the AF brings that point into focus and bingo, I’ve metered from one point and exposed for another. I find this useful for example where the subject is in the foreground and the background has light and dark areas.