BBF and Matrix Metering Question

[Stacy Morin]

I have been trying to master Back Button Focusing, quite honestly my camera has been in it for 3 or so years. All of which I have been unsure as to how and why it is supposed to give you the sharpest possible pictures. (I have yet to find that to be true-sigh)
I also recently enrolled in a course through Better Photography for my Nikon D7000 camera. In the notes the instructor made mention that Matrix metering is not ideal for BBF. I asked him about it and this is what he wrote me back:

"Hi Stacy,

Matrix metering takes a number of factors into account when calculating the exposure, including the scene brightness, the scene's contrast level, colours and information from the autofocusing system; therefore if you meter using Matrix from one scene and then lock the exposure using the AE-L feature before re-composing to shoot an alternative scene you may well find that the exposure for the second scene is not accurate. The AE-L feature works most reliably with either Spot, or Center-weighted metering,as these do not integrate information from the autofocusing system, and they are not colour sensitive."

Do you all agree with this and find it to be true? I also still struggle what "re-compose" the shot means. Can someone hear explain? Thanks!

 

[Mach0]

You mean focus and recompose rather than bbf. Depends on the scene and subject. I personally use center weighted unless I'm doing scenery ( which I almost NEVER DO)


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[KmH]

Re-compose is where you focus, lock focus, and then move the camera so the point of focus is in a different p[lace in the scene you're about to photograph.
You have 'recomposed' the shot.

This is often done so focus can be achieved using a more accurate cross-type focus point rather than a regular focus point.

See pages 105 - 108 of your D7000 user manual for more info about the 3 light metering options your D7000 has, Autoexposure lock, and Exposure Compensation.

 

[Vince.1551]

Put it simply your main subject is not in the center when you click the shutter so you would want to focus on the main subject first and then move him/her/it to let's say one of the corners of the photo.


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[Designer]

Stacy; for what it's worth, I just use the shutter button. Press part way, the camera will focus where you hold the focus (mine is an area not a cross) then without moving my finger I recompose the shot and finish pressing the shutter button. Works for me.

 

[JacaRanda]

Don't make it more complicated than it is. The back button is simply a different button to use instead of the shutter button half press. Using either with good technique should both yield the same sharpness in your photos (all other things being equal).

You may want to think about changing your settings from bbf back to the shutter button. Depending on the weight of your camera and lens, you may not be able to hold the camera steady enough to have your thumb in a not so normal position.

This is where it would be great if you could post some pictures and exif data.

 

[Stacy Morin]

Don't make it more complicated than it is. The back button is simply a different button to use instead of the shutter button half press. Using either with good technique should both yield the same sharpness in your photos (all other things being equal).

You may want to think about changing your settings from bbf back to the shutter button. Depending on the weight of your camera and lens, you may not be able to hold the camera steady enough to have your thumb in a not so normal position.

This is where it would be great if you could post some pictures and exif data.

Oh dear, I do tend to do that! I will try to post a pic later-I have officially gone back to Shutter and turned off BBF.

 

[TCampbell]

There are two entirely different concepts going on here... one is the "metering" discussing... another is "focus".

Your instructor is effectively saying "If I meter this subject over here in the bright sunlight and lock my exposure... then re-compose by pointing my camera over here to this dark shadowy area... then I may end up with an underexposed image." That's understandable if the lighting different. The intention is that the lighting is being "locked" to a subject of interest and when you re-compose you don't want the camera to re-meter and set exposure on a composition which would cause your intended subject to be over or under-exposed.

As for back-button focus... that's something else completely.

Ordinarily a camera will both focus AND meter when you half-press the shutter button. Sports photographers complained of a particular problem and it goes something like this:

They're tracking some athlete running down the field using AF-C (Nikon) or AI-Servo (Canon) so that the camera is continuously both metering and tracking focus on their subject. As they get to the point where something exciting is happening and they want those shots... SUDDENLY a nearer player enters the scene and that player is a bit closer to the camera so the camera switches focus to them. This isn't the subject you wanted to capture...so your intended subject is out of focus and the shot is missed. Now the photographer is frustrated because they know what they want... they just need to get the camera to do it.

By changing to "back button focus", the dynamic is changed. You can continue to hold your finger half-pressed on the shutter for metering purposes... but the camera will only activate the focus system when you press the back-button. That means that you can tap (or hold) the focus button to update the focus as needed and if a distracting subject enters the frame you can just "release" the back-button. The camera will continue to meter AND you can continue to shoot... but it won't update the focus until you push the back-button again.
​

This means you get to separate the "focus" button so that it's not on the SAME button as is used for metering and shooting. Now YOU can control when the camera updates focus (even in a continuous focusing mode.)

 

[curtyoungblood]

It sounds to me like your instructor doesn't understand how BBF focus and/or the AE-L/AF-L button on your D7000 works. If you set that button to AF-ON (which is the setting you'd want to use for BBF), then it won't perform an exposure lock anymore.

 

[Derrel]

Stacy, You might find some of this plain-English discussion of the D7000's control options to be helpful. Nikon D7000 Custom Setting Menu

Take note at f3 and f5; there are multiple ways to combine or isolate the locking of the metering and or the focusing lock operations.

 

[Stacy Morin]

Stacy, You might find some of this plain-English discussion of the D7000's control options to be helpful. Nikon D7000 Custom Setting Menu

Take note at f3 and f5; there are multiple ways to combine or isolate the locking of the metering and or the focusing lock operations.

This was helpful! I have never assigned the Function Button or Preview button. Do You? I tried doing what Ken Rockwell does but couldn't figure it out. Once I hit f3-I only get the option of 1 step spd/aperture. Any ideas on this Derrel?