Evaluative Meter = TERRIBLE for 'Focus & Recompose'

Started Apr 25, 2012 | Discussions
cs hauser Contributing Member • Posts: 735
Evaluative Meter = TERRIBLE for 'Focus & Recompose'

Focus & Recompose is a common technique among photographers. Unfortunately, evaluative metering FAILS whenever that method is employed. It doesn't matter whether the camera is using default settings, or if it's configured to separate exposure lock from focus lock (via the AF-On button).

In the following cases, we assume One-Shot AF Mode with manual AF point selection.

CASE 1: Camera defaults to locking focus & exposure with half-press of shutter button

  • We half-press the shutter button to lock both focus & exposure. We recompose. We press the AE-Lock button to re-meter for the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

CASE 2: Camera is set up so that AF-On button locks focus, and a half-pressed shutter button takes a meter reading.

  • We press the AF-On button to lock focus. We release AF-On button to stop focus. We recompose. We half-press shutter button to meter the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

It seems to me that evaluative metering will never work properly with "focus & recompose". I don't see any way around it. There is no custom function to unlink the selected AF point from the exposure meter. This is a particularly nasty flaw for the 5D & 5D2, since "focus & recompose" is a necessity with these cameras.

The most convenient workaround is to lock exposure before recomposing. But this will result in an exposure that is not optimal for the recomposed scene.

What the camera SHOULD be doing is memorize the meter reading at the active AF point when focus is achieved (i.e. the subject). Then every subsequent meter reading should be skewed towards this memorized value. This memorized value will not be erased until the next time the camera starts auto-focus, presumably with a new subject.

Canon EOS 5D Canon EOS 5D Mark II
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tmr Senior Member • Posts: 1,520
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

That would be a good default setting or at least an option. Another possibility would be a user selectable AE zone that gets additional weighting similar to center weighted average, but with the user selected zone replacing the center region for the higher weighting.

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tony field Veteran Member • Posts: 9,469
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

cs hauser wrote:

...

The most convenient workaround is to lock exposure before recomposing. But this will result in an exposure that is not optimal for the recomposed scene.

All of the metering methods work as I expect.

On the 5D-II:
C.FnIV-1 set to 3
C.FnIV-2 set to 1

On the 5D-II (and almost always on the 1D-IV) I use centre point focus only.

Pressing the shutter button 1/2 way locks the exposure as desired. keep pressed.
Locate the subject for focus and press AF-on. Focus is locked as expected.
Recompose and continue to press the shutter button for release.

To me, this makes sense and works as expected.

I have always found evaluative to be erratic. I prefer average, spot, and small spot.

What the camera SHOULD be doing is memorize the meter reading at the active AF point when focus is achieved (i.e. the subject). Then every subsequent meter reading should be skewed towards this memorized value. This memorized value will not be erased until the next time the camera starts auto-focus, presumably with a new subject.

I don't quite follow this logic.

What I would like to see is the old Nikon style of buttons with AF-on and AE-lock as two independent operations.

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Great Bustard Forum Pro • Posts: 41,906
Use the * key for focus lock, shutter half-press for exposure lock. (nt)

cs hauser wrote:

Focus & Recompose is a common technique among photographers. Unfortunately, evaluative metering FAILS whenever that method is employed. It doesn't matter whether the camera is using default settings, or if it's configured to separate exposure lock from focus lock (via the AF-On button).

In the following cases, we assume One-Shot AF Mode with manual AF point selection.

CASE 1: Camera defaults to locking focus & exposure with half-press of shutter button

  • We half-press the shutter button to lock both focus & exposure. We recompose. We press the AE-Lock button to re-meter for the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

CASE 2: Camera is set up so that AF-On button locks focus, and a half-pressed shutter button takes a meter reading.

  • We press the AF-On button to lock focus. We release AF-On button to stop focus. We recompose. We half-press shutter button to meter the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

It seems to me that evaluative metering will never work properly with "focus & recompose". I don't see any way around it. There is no custom function to unlink the selected AF point from the exposure meter. This is a particularly nasty flaw for the 5D & 5D2, since "focus & recompose" is a necessity with these cameras.

The most convenient workaround is to lock exposure before recomposing. But this will result in an exposure that is not optimal for the recomposed scene.

What the camera SHOULD be doing is memorize the meter reading at the active AF point when focus is achieved (i.e. the subject). Then every subsequent meter reading should be skewed towards this memorized value. This memorized value will not be erased until the next time the camera starts auto-focus, presumably with a new subject.

OP cs hauser Contributing Member • Posts: 735
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

tony field wrote:

All of the metering methods work as I expect.

On the 5D-II:
C.FnIV-1 set to 3
C.FnIV-2 set to 1

On the 5D-II (and almost always on the 1D-IV) I use centre point focus only.

Pressing the shutter button 1/2 way locks the exposure as desired. keep pressed.
Locate the subject for focus and press AF-on. Focus is locked as expected.
Recompose and continue to press the shutter button for release.

Evaluative metering is biased heavily towards the selected AF point, because the camera assumes that AF point is directed at your subject. If you take a meter reading and your subject is not under that AF point, then the camera will foolishly try to expose for whatever random object happens to be under that point (even if it's not in focus).

If you had carefully read what I originally wrote, you would already know why your method is flawed. I don't feel like re-writing everything that I already wrote. If you re-read it, you would know why your method is wrong. You end up having a meter reading that is heavily skewed towards some random object.

OP cs hauser Contributing Member • Posts: 735
Sheesh... you people don't read before replying :)

Sheesh... I guess you people don't bother reading before replying.

I already know how to lock exposure and lock focus separately. It causes problems with evaluative metering. That was the whole point of my post.

Horshack Veteran Member • Posts: 6,593
Potential solution

After reading your OP I though it over and a potential solution occurred to me. I wondered what evaluative metering would do if you set the AF selection mode to automatic (mode where all the AF points light up) but don't actually acquire focus after setting it to automatic. In that state there is no active AF point until you attempt AF for the first time. I did some quick metering experiments and it appears the camera is not applying any AF-point weighting when it's in automatic AF selection mode and no AF point has been acquired yet. I'm assuming it's still performing an evaluative meter but without an AF-point weighting. Switching between automatic and center point is rather easy on both bodies so one could switch back and forth during the shooting process when needing to alternate between focusing and metering. Here's the workflow:

  • I have my shutter/AF-on button configured for option 3, where a half-press of the shutter locks the meter and AF-ON starts AF

  • With the center AF active, do you focusing by pressing AF-ON. Release AF-ON when focus is acquired

  • Before/during recomposing, press the AF point selection button to activate the AF point selection and then turn the top dial one click left to select automatic AF selection mode

  • When you've finalized your composition, the evaluative meter reading will reflect your composition without any AF weighting. You can either take the photo then by full-pressing the shutter or you can lock the exposure with a shutter half-press if you still want to perform any changes to the composition but with the exposure locked.

  • Before focusing for the next shot, switch back to center AF by the pressing AF point selection button and turning the top dial one click to the right.

You can also use the quick-control dial to more quickly switch between automatic and center AF points. On the 5DM2 configure C.Fn III.3 "AF point selection method" to "Quick Control Dial direct". On the 5D its Custom Function 13. With that configured you can switch between auto/center with one turn of the quick control dial.

tony field Veteran Member • Posts: 9,469
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

cs hauser wrote:

tony field wrote:

All of the metering methods work as I expect.

On the 5D-II:
C.FnIV-1 set to 3
C.FnIV-2 set to 1

On the 5D-II (and almost always on the 1D-IV) I use centre point focus only.

Pressing the shutter button 1/2 way locks the exposure as desired. keep pressed.
Locate the subject for focus and press AF-on. Focus is locked as expected.
Recompose and continue to press the shutter button for release.

Evaluative metering is biased heavily towards the selected AF point, because the camera assumes that AF point is directed at your subject. If you take a meter reading and your subject is not under that AF point, then the camera will foolishly try to expose for whatever random object happens to be under that point (even if it's not in focus).

Yes. That it the way it works. If you are foolish, you will point the metering at some random place.

If you understand how you metering/focus system works, then it is easy to utilize in a logical fashion. It is necessary to determine the sequence of events of events that will result in an appropriate exposure. I choose exposure, focus, recompose, shoot as the correct sequence. There are trivially other sequences that work as well.

If you had carefully read what I originally wrote, you would already know why your method is flawed. I don't feel like re-writing everything that I already wrote. If you re-read it, you would know why your method is wrong. You end up having a meter reading that is heavily skewed towards some random object.

I did read carefully. Seems you do not. I merely pointed out the workflow of shooting that can result in appropriate exposure.

My method is not "flawed". The objective is to take the meter reading from an appropriate area (not random) that is will deliver the right exposure for the scene. Maybe you point to random areas and pray - I suggest that you try to figure out how the meter (any mode) actually works and learn where to point the meter.

You seems to assume that evaluative should be magical and do as your imagination would like it to do.
--
tony
http://www.tphoto.ca

Great Bustard Forum Pro • Posts: 41,906
More often than not. : )

cs hauser wrote:

Sheesh... I guess you people don't bother reading before replying.

Please don't tell me that surprises you.

I already know how to lock exposure and lock focus separately. It causes problems with evaluative metering. That was the whole point of my post.

How so? Half-shutter press where you want the exposure locked, * where you want the focus locked, full press to take the shot.

BrianPriceUK Contributing Member • Posts: 760
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

Your problems will only occur if you are not focussing on the subject, but some other point in the frame. I suppose you may sometimes want the subject out of focus, but how often?

Brian

jrsforums Contributing Member • Posts: 979
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

In Case 1, why are you remetering with the AF-ON button after you had already successfully focused and metered on the subject....with your set up, you need to AF-on at the same time you lock focus, then recompose.

I have AF-on set to focus and shutter to meter and lock metering.

John

cs hauser wrote:

Focus & Recompose is a common technique among photographers. Unfortunately, evaluative metering FAILS whenever that method is employed. It doesn't matter whether the camera is using default settings, or if it's configured to separate exposure lock from focus lock (via the AF-On button).

In the following cases, we assume One-Shot AF Mode with manual AF point selection.

CASE 1: Camera defaults to locking focus & exposure with half-press of shutter button

  • We half-press the shutter button to lock both focus & exposure. We recompose. We press the AE-Lock button to re-meter for the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

CASE 2: Camera is set up so that AF-On button locks focus, and a half-pressed shutter button takes a meter reading.

  • We press the AF-On button to lock focus. We release AF-On button to stop focus. We recompose. We half-press shutter button to meter the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

It seems to me that evaluative metering will never work properly with "focus & recompose". I don't see any way around it. There is no custom function to unlink the selected AF point from the exposure meter. This is a particularly nasty flaw for the 5D & 5D2, since "focus & recompose" is a necessity with these cameras.

The most convenient workaround is to lock exposure before recomposing. But this will result in an exposure that is not optimal for the recomposed scene.

What the camera SHOULD be doing is memorize the meter reading at the active AF point when focus is achieved (i.e. the subject). Then every subsequent meter reading should be skewed towards this memorized value. This memorized value will not be erased until the next time the camera starts auto-focus, presumably with a new subject.

HSU Regular Member • Posts: 345
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

First I have to state, that all metering-methods work for me as awaited. I have absolutely no problem to get good shots with all of them.

The most convenient workaround is to lock exposure before recomposing. But this will result in an exposure that is not optimal for the recomposed scene.

Thats what I use most. The metering is mostly fine, if not, I'll have to use my own brain and correct for that.

What the camera SHOULD be doing is memorize the meter reading at the active AF point when focus is achieved (i.e. the subject). Then every subsequent meter reading should be skewed towards this memorized value. This memorized value will not be erased until the next time the camera starts auto-focus, presumably with a new subject.

I think, that would do more worse than good, since then you end with a metering-system which will behave absolutely unpredictable (evaluative is already on the border of being predictable). And everything unpredictable makes it harder to get what you want, IMHO.

And from my experience from machine learning I can assure you, that every hack (and what you propose is nothing more than a simple hack) produces more unwanted side-effects than it's doing good.

What could be done, would use optical flow to connect the camera movement with the metering point and therefore keep track of it. But I think that would give further problems (what if the metering point moves differently/independently? What if the camera gets moved further, so that the original metering-point gets out of view? Also that would need really high-res metering sensors (and therefore would cost a lot more). In live-view that should already be possible today (yet very experimental).

=> I'd say: forget about it. Learn to predict what your metering will get, and meter for something usable, compensate, or even go for manual mode in very difficult situations).

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f_stops Contributing Member • Posts: 565
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

tony field wrote:

cs hauser wrote:

tony field wrote:

If you understand how you metering/focus system works, then it is easy to utilize in a logical fashion. It is necessary to determine the sequence of events of events that will result in an appropriate exposure. I choose exposure, focus, recompose, shoot as the correct sequence. There are trivially other sequences that work as well.

If you had carefully read what I originally wrote, you would already know why your method is flawed. I don't feel like re-writing everything that I already wrote. If you re-read it, you would know why your method is wrong. You end up having a meter reading that is heavily skewed towards some random object.

I did read carefully. Seems you do not. I merely pointed out the workflow of shooting that can result in appropriate exposure.

My method is not "flawed". The objective is to take the meter reading from an appropriate area (not random) that is will deliver the right exposure for the scene. Maybe you point to random areas and pray - I suggest that you try to figure out how the meter (any mode) actually works and learn where to point the meter.

Sorry CS, reread Tony's post. He is correct - you missed the point.

Furthermore, the evaluative metering is not 'spot' reading the AF point. You are correct that metering will change (a bit) if the recompose spot shifts to a different EV value - but in practice the EV values need to be different by a significant amount. .

My first solution to your problem is to shoot in manual mode. I don't consider this a problem, just a consideration on how the metering system works. Tony's solution is another approach if you prefer auto metering.

This effect is much more noticeable on my M9, where the metering is a true wide-spot meter. Canon's evaluative metering does a fairly good job of getting exposure correct using focus-recompose in most situations.

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Walter Contributing Member • Posts: 503
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

Dramatic headline! I'll bet Ansel is laughing somewhere....he set up a plate camera in a huge rush to get his Moonrise over Hernandez.... managed to focus and guess the exposure and crack off a couple of shots before it disappeared.

A photographer should be an artist and craftsman who makes wonderful pictures that move people. Evaluative metering used to be done by the photographer now we expect the camera to do it all..

Ansel wrote:

The Zone System has often been thought to apply only to certain materials, such as black-and-white sheet film and black-and-white photographic prints. Adams (1981, xii) suggested that when new materials become available, the Zone System is adapted rather than discarded. He anticipated the digital age, stating

I believe the electronic image will be the next major advance. Such systems will have their own inherent and inescapable structural characteristics, and the artist and functional practitioner will again strive to comprehend and control them.

Walter

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risbac Regular Member • Posts: 365
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

Evaluative metering is not any worse for "focus & recompose" than for any shot without recompose ! It will always work within the limits of your AF system :

If you can have the perfect framing AND one of the AF spot exactly where you want to focus AND the metering evaluation being perfect for your shot, then it will work fine. That's already 3 conditions to get, not so easy, right ? For the last one, I mean that even if you have the perfect framing & AF, who knows if the exposure will be perfect ? Most of the time, it will be, but not always depending of what you want to achieve with the photo. So even with perfect conditions, it still relying on the number of AF points that you have, and some luck. Most of the time, I'm sure one would like to be able to frame, then to tell the camera "ok, do your metering here, between those two AF points". It can't work this way... No matter if you are recomposing or not, this problem exists, right ?

That's why we have manual exposure. And exposure compensation. We should ALL be able to see if after recomposing the exposure will be way off. Especially with Canon, where this evaluative metering is not changing that much if you recompose a bit. Compared to the Nikon metering, I think the bias is much smaller.
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Jeff Palmucci Regular Member • Posts: 127
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

On the 5d3, in evaluative mode and one shot, focus and metering is locked on the shutter half press. (Other modes, however, still work incorrectly, as you describe.)

loafer Senior Member • Posts: 1,505
"compose & refocus"

1. Compose shot first - meter with half press or *
2. move camera to focus with back button AF
3. move camera back and shoot.

Michael Thomas Mitchell Forum Pro • Posts: 11,747
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

So much for all those fabulous focus points.

cs hauser wrote:

Focus & Recompose is a common technique among photographers. Unfortunately, evaluative metering FAILS whenever that method is employed. It doesn't matter whether the camera is using default settings, or if it's configured to separate exposure lock from focus lock (via the AF-On button).

In the following cases, we assume One-Shot AF Mode with manual AF point selection.

CASE 1: Camera defaults to locking focus & exposure with half-press of shutter button

  • We half-press the shutter button to lock both focus & exposure. We recompose. We press the AE-Lock button to re-meter for the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

CASE 2: Camera is set up so that AF-On button locks focus, and a half-pressed shutter button takes a meter reading.

  • We press the AF-On button to lock focus. We release AF-On button to stop focus. We recompose. We half-press shutter button to meter the recomposed scene.

  • PROBLEM: The new exposure will be biased heavily towards the selected AF point, as if it's still pointing at our subject. But we have already recomposed, and the selected AF point is no longer pointing at the subject! The meter will be skewed to expose for whatever random object happens to be under the selected AF point.

It seems to me that evaluative metering will never work properly with "focus & recompose". I don't see any way around it. There is no custom function to unlink the selected AF point from the exposure meter. This is a particularly nasty flaw for the 5D & 5D2, since "focus & recompose" is a necessity with these cameras.

The most convenient workaround is to lock exposure before recomposing. But this will result in an exposure that is not optimal for the recomposed scene.

What the camera SHOULD be doing is memorize the meter reading at the active AF point when focus is achieved (i.e. the subject). Then every subsequent meter reading should be skewed towards this memorized value. This memorized value will not be erased until the next time the camera starts auto-focus, presumably with a new subject.

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joema1
joema1 Contributing Member • Posts: 711
Re: Evaluative Meter = TERRIBLE for 'Focus & Recompose'

cs hauser wrote:

...It seems to me that evaluative metering will never work properly with "focus & recompose". I don't see any way around it. There is no custom function to unlink the selected AF point from the exposure meter. This is a particularly nasty flaw for the 5D & 5D2, since "focus & recompose" is a necessity with these cameras.

Doesn't Nikon's matrix metering work the same way? I think it also biases exposure toward the current AF point, so focus and recompose won't produce optimal metering.

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wolfpuppies3 Senior Member • Posts: 1,747
Duh

Of course it does. It is evaluative not spot.
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