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Thread: New to cs... Evaluative metering

  1. #41
    Senior Member edutilos-'s Avatar
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    Quote Originally Posted by mengwei11

    Ok, now I'm getting confused. Somebody else posted that when u half press the shutter, u lock the shutter speed and aperture setting (ie exposure) so does it or not?

    If it doesn't like u said, why does the same scene have different exposure when I focus lock on either bright sky or dark tree and recompose to the same scene and the metering is set on evaluative.
    Sorry, I might have made a mistake. All my cameras are set that way (AE lock linked to AF lock) forgot it is a conscious option after so long. The rest are right. Apologize for the mistake.

  2. #42
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by mengwei11 View Post
    Ok, now I'm getting confused. Somebody else posted that when u half press the shutter, u lock the shutter speed and aperture setting (ie exposure) so does it or not?

    If it doesn't like u said, why does the same scene have different exposure when I focus lock on either bright sky or dark tree and recompose to the same scene and the metering is set on evaluative.
    I using a 50D. by default when you had chosen a focus point and you half-depress shutter, you lock both focus and exposure. Of course you can change that in custom function.

    As for evaluative metering, in simple english :- means it's Canon metering design to guess what's your main subject. It goes by dividing it into zones and try to expose the main subject correctly.

  3. #43
    Moderator ziploc's Avatar
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by mengwei11 View Post
    Ok, now I'm getting confused. Somebody else posted that when u half press the shutter, u lock the shutter speed and aperture setting (ie exposure) so does it or not?

    If it doesn't like u said, why does the same scene have different exposure when I focus lock on either bright sky or dark tree and recompose to the same scene and the metering is set on evaluative.
    If you're using spot metering, then most likely you would want to keep the exposure when recomposing, since the subject you spot meter on will be the exposure you want to achieve (e.g. the main subject or a 18% grey card). So in this case locking AE while half press shutter release is ok.

    On the other hand, if you're using evaluative metering, let's say you're using center focusing point. You focus on the subject with it at the center, and then recompose to place it at the thirds. Now imagine the background to one side of the subject is dark while the other side is bright. By recomposing, you have now shifted the subject and hence either more light or less light (depending which side you're shifting) enters the camera. If in this case you lock the AE while focusing, the final exposure after recomposing will be incorrect.

  4. #44
    Moderator ziploc's Avatar
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by Snowcrash View Post
    I using a 50D. by default when you had chosen a focus point and you half-depress shutter, you lock both focus and exposure. Of course you can change that in custom function.
    Yes you're right, for Canon camera this is the case, as long as you're in One Shot AF and evaluative metering. See here.

    On the other hand in Nikon cameras, the default for exposure lock at half press shutter is off, and it needs to be specifically turned on in custom menu. So different manufacturer does it differently. But I do find Nikon's more logical not to lock the AE in matrix metering due to the reason given above.

  5. #45

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    Ok I've been experimenting and this is my layman findings. I think most of u have been explaining this to me, just that I need to sort of articulate it back so that I understand.

    Using evaluative metering
    - with my 50d where u focus lock is also where you meter lock. The *lock has no effect on evaluative
    - when I focus lock / meter lock on the subject, the exposure is locked. Hence if I focused on sky, but then recomposed where a dark tree is in the picture, the picture is underexposed (becos the camera has locked an exposure to compensate for the bright sky)

    Using spot metering
    - this is where the * ae lock makes a difference. But it only makes a difference if your focus point and metering point is different! (which is not what a lot of mags and people say!)
    - if your focus point and metering point is the same, when u half depress the shutter to lock focus, exposure is already locked, so no need to depress *
    - but if u want to meter for say the sky, then u *ae lock at the sky, recompose and focus on subject and fire off. The picture will have the exposure based on the sky. I know this is a lousy example, and I'm wondering now, when would ae lock be useful.

    Ok I think I understand now. Sorry for being slow.

  6. #46

    Default Re: New to cs... Evaluative metering

    In other words, the half-press button works differently in Nikon and Canon. Generally, in Auto mode, the shutter button works for both AF and AE, but in full Manual mode, the half-press button depends on the settings made.

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    Senior Member ZerocoolAstra's Avatar
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by mengwei11 View Post
    Ok I've been experimenting and this is my layman findings. I think most of u have been explaining this to me, just that I need to sort of articulate it back so that I understand.

    Using evaluative metering
    - with my 50d where u focus lock is also where you meter lock. The *lock has no effect on evaluative
    - when I focus lock / meter lock on the subject, the exposure is locked. Hence if I focused on sky, but then recomposed where a dark tree is in the picture, the picture is underexposed (becos the camera has locked an exposure to compensate for the bright sky)

    Using spot metering
    - this is where the * ae lock makes a difference. But it only makes a difference if your focus point and metering point is different! (which is not what a lot of mags and people say!)
    - if your focus point and metering point is the same, when u half depress the shutter to lock focus, exposure is already locked, so no need to depress *
    - but if u want to meter for say the sky, then u *ae lock at the sky, recompose and focus on subject and fire off. The picture will have the exposure based on the sky. I know this is a lousy example, and I'm wondering now, when would ae lock be useful.

    Ok I think I understand now. Sorry for being slow.
    the way I am understanding your post, is different from what ziploc stated in post #43.
    He's saying that the AE-lock feature is useful when paired with evaluative metering, not spot metering.
    Exploring! :)

  8. #48
    Moderator ziploc's Avatar
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by ZerocoolAstra View Post
    the way I am understanding your post, is different from what ziploc stated in post #43.
    He's saying that the AE-lock feature is useful when paired with evaluative metering, not spot metering.
    Actually I meant it the other way round, meaning pairing AE lock with spot (or center weighted) metering is more desirable, and not so with evaluative.

    I remember reading this mentioned specifically in one of the Nikon manual (regarding not to lock AE when using matrix metering)... but I can't remember which one. I owned an F90, F5, Fuji S2 (D80) before, and now the Fuji S5 (D200), so it must be one of them... The older manual has better explanation regarding the matrix metering as well, with pictures as illustration (think it was the F90).
    Last edited by ziploc; 17th February 2011 at 03:37 PM.

  9. #49

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    Quote Originally Posted by ziploc

    Actually I meant it the other way round, meaning paring with spot (or center weighted) metering is more desirable, and not so with evaluative.

    I remember reading this mentioned specifically in one of the Nikon manual (regarding not to lock AE when using matrix metering)... but I can't remember which one. I owned an F90, F5, Fuji S2 (D80) before, and now the Fuji S5 (D200), so it must be one of them... The older manual has better explanation regarding the matrix metering as well, with pictures as illustration (think it was the F90).
    In canon the ae lock has no effect in evaluative. I'm so happy I sort of understand now.

  10. #50
    Senior Member ZerocoolAstra's Avatar
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by ziploc View Post
    Actually I meant it the other way round, meaning pairing AE lock with spot (or center weighted) metering is more desirable, and not so with evaluative.

    I remember reading this mentioned specifically in one of the Nikon manual (regarding not to lock AE when using matrix metering)... but I can't remember which one. I owned an F90, F5, Fuji S2 (D80) before, and now the Fuji S5 (D200), so it must be one of them... The older manual has better explanation regarding the matrix metering as well, with pictures as illustration (think it was the F90).
    oh?
    I kinda agreed with your earlier point of view
    To me, when using spot or center-weighted metering, it makes sense to couple metering and exposure-lock together with a single half-press of the shutter release. I would use this when capturing a portrait, for example.
    Both accurate focus and exposure on my subject are most important to me, even though I would re-compose to have the subject at an intersection of the thirds for example.
    Exploring! :)

  11. #51
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by mengwei11 View Post
    ......and I'm wondering now, when would ae lock be useful.....
    It's good when shooting backlit subjects when using Spot or Center-Weighted Metering in conjunction with Spot or Center AF
    Last edited by Diavonex; 17th February 2011 at 05:29 PM.

  12. #52

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    Quote Originally Posted by Diavonex

    It's good when shooting backlit subjects when using Spot or Center-Weighted Metering
    That's what I thought. But it doesn't seem to be the case. Subject against backlit background. U set to spot meter. U focus on subject, the exposure is locked. UNLESS you want to meter for the backlit, but focus on the subject, but I don't understand why you will do that.

  13. #53
    Senior Member Diavonex's Avatar
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by mengwei11 View Post
    That's what I thought. But it doesn't seem to be the case. Subject against backlit background. U set to spot meter. U focus on subject, the exposure is locked. UNLESS you want to meter for the backlit, but focus on the subject, but I don't understand why you will do that.
    If the subject is off-center, you lock exposure and focus, recompose and shoot. Subject will be correctly exposed and focused.

  14. #54
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by Diavonex View Post
    If the subject is off-center, you lock exposure and focus, recompose and shoot. Subject will be correctly exposed and focused.
    TS is asking for the merits of de-coupling the focus and exposure locks.
    Yours is the perfect example of when it is a good idea to couple the focus and exposure together
    Exploring! :)

  15. #55
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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by ZerocoolAstra View Post
    TS is asking for the merits of de-coupling the focus and exposure locks.
    Yours is the perfect example of when it is a good idea to couple the focus and exposure together
    I've edit my reply:

    It should be using Spot or Center-Weighted Metering in conjunction with Spot or Center AF.

  16. #56
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    Default Re: New to cs... Evaluative metering

    I'm confused liao
    Seems to have gone off on a tangent. Will stop here before I confuse myself further

  17. #57

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    Quote Originally Posted by Diavonex

    If the subject is off-center, you lock exposure and focus, recompose and shoot. Subject will be correctly exposed and focused.
    All I'm saying is that in my 50d, when u lock focus u lock exposure. U only use ae lock if your meter point if not your subject.

  18. #58
    Senior Member Diavonex's Avatar
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    Default Re: New to cs... Evaluative metering

    I'm also confused; will hold my horses

  19. #59

    Default Re: New to cs... Evaluative metering

    what the... i am lost in a whirlpool..

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    Default Re: New to cs... Evaluative metering

    Quote Originally Posted by mengwei11 View Post
    That's what I thought. But it doesn't seem to be the case. Subject against backlit background. U set to spot meter. U focus on subject, the exposure is locked. UNLESS you want to meter for the backlit, but focus on the subject, but I don't understand why you will do that.
    You'd do that if you want to shoot a silhouette with a nicely exposed sunset in the background (for example). Need to meter on the sky, but focus on the silhouette. Something like this:


    If the camera tried to meter to retain some details in the silhouette (the subject in focus), the sky would be blown out, or at least overexposed and the mood would be completely different.
    My photos - see just some or all of it =)

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