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Thread: False metering ?

  1. #1

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    False metering ?

    Hi,
    I took some test shots with my new Canon 50mm f/1.4 lens of the same subject (flower) and distance
    using the same settings ISO 800; f/2.8 same, M focus same but with shutter speed 1/250; 1/350 and 1/4000
    The picture got correctly somewhat darker on the 1/350sec but a lot lighter with 1/4000sec.
    Am I missing something here ? Please tell me how this could happen .

    Patrik

  2. #2
    arith's Avatar
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    Re: False metering ?

    that is 4 stops darker, it is impossible unless the light improved by 5ev.

  3. #3
    Moderator GrumpyDiver's Avatar
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    Re: False metering ?

    I don't know the fine details of the Canons, but did you turn off your automatic ISO adjustment? I had a somewhat similiar issue where the camara tried to crank up the ISO when my aperture / shutter speed did not allow for a "correct" exposure.

  4. #4
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    Re: False metering ?

    Hi Patrik,

    There are a few things that could be happening. What camera are you using? Did you use Manual mode to change the shutter speed? I have interpreted your post as stating you used Manual focus but I am unclear about the exposure mode (although using a constant f2.8 would imply Manual mode).

    It is possible that one or either of Canon's 'Auto lighting optimiser' or 'Safety shift' are being applied. The first affects JPEGs in camera and the second should not affect Manual mode but will apply in Av/Tv mode. A few more details on your test would help.

    Also I have to ask if you used flash with one or any of the shots? If so then the camera may adjust the shutter speed to the fastest sync speed possible with your camera. This would be way below 1/4000 (probably 1/250s or 1/200s) and so the image will look much brighter than you expect.

    Alex

  5. #5

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    Re: False metering ?

    You must be right thanks. I saw this the day after and must have used a filter and forgotten it.

  6. #6

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    Re: False metering ?

    Thanks for your help Alex. I use a Canon 60D, had it in Manual mode w. spot metering. Pictures taken both in RAW and jpeg with the same effect. No flash was used. I seem to be confused that I dialed in 1/4000sec which I cannot remember doing but that's what the EXIF data shows .

  7. #7

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    Re: False metering ?

    Quote Originally Posted by GrumpyDiver View Post
    I don't know the fine details of the Canons, but did you turn off your automatic ISO adjustment? I had a somewhat similiar issue where the camara tried to crank up the ISO when my aperture / shutter speed did not allow for a "correct" exposure.
    Well here are (attached) jpg previews of all the three photos, detective.
    Rgs/Patrik

  8. #8

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    Re: False metering ?

    Quote Originally Posted by pat3pee View Post
    Well here are (attached) jpg previews of all the three photos, detective.
    Rgs/Patrik
    Not seeing any attached images

  9. #9
    Moderator Dave Humphries's Avatar
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    Re: False metering ?

    Quote Originally Posted by pat3pee View Post
    Well here are (attached) jpg previews of all the three photos, detective.
    Rgs/Patrik
    Hi Patrik,

    We don't see any images I'm afraid.

    Have a look at this thread which details four different ways to display images at CiC.
    HELP THREAD: How can I post images here?

    Just be sure to follow all of the steps in whichever method you choose, it is a two stage process; upload the picture to somewhere, then put a link to the picture into the post - many people that have problems stop too soon and miss the second part. Even I did, which is why I wrote the instructions

    Welcome to the CiC forums from ....

  10. #10

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    Re: False metering ?

    Sorry Colin, I'm new at this. Will make another try+

    False metering ?

  11. #11
    Moderator Dave Humphries's Avatar
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    Re: False metering ?

    Hi Patrik,

    Well I'm stumped too, I'm not a Canon shooter, but the sun looks to be shining in all three, all other figures are equal, so why the left hand one (with supposedly a much shorter exposure) is so much brighter is a mystery to me.

    Cheers,

  12. #12
    William W's Avatar
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    Re: False metering ?

    I suggest this procedure:

    1. Peripheral Illumination Correction

    With the lens attached to the 60D, open the First Camera Menu and scroll to “Peripheral illumin. Correct.” – press “SET”
    Select “Disable” – press “SET”
    Close that menu.


    2. Auto Lighting Optimizer

    Open the Second Camera Menu and scroll to “Auto Lighting Optimizer”. – press “SET”
    Select the icon on the left of the screen “OFF”. – Press “SET”


    3. Bracketing

    Whilst still in the Second Camera Menu, scroll to “Expo.comp./AEB”. – Press “SET”
    If not already in the centre, select the AEB amount such that the bar line appears ONLY at the CENTRE POSITION. Press “SET”
    Close that menu.


    4.
    Repeat your test ensuring that the light is constant and the same for each test exposure.

    The results of this second test will confirm or not, if one or a combination of these camera Functions is the cause of your first test result.

    If you are unsure of these Camera Functions and the Enable/Disable procedures, refer to the Bolded and Underlined Topics, in your 60D User Manual.

    WW
    Last edited by William W; 3rd April 2012 at 02:26 AM. Reason: Added topic headings for easy look up

  13. #13

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    Re: False metering ?

    I see that you are using spot metering in all three images. Can you check with the images where the exposure was taken from. Either use AF point enable in the menu, or else look in Zoombrowser. I suspect that the left image was exposed on the dark stem or dark brown brick, while the others were on various parts of the flower. Try again using evaluative metering and see if you get the same results at different shutter speeds

  14. #14
    William W's Avatar
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    Re: False metering ?

    Ken,

    The METERING MODE and also the whole of the camera's TTL metering system would appear to be irrelevant - considering:

    1. The OP stated in post #6, that MANUAL CAMERA MODE was used.
    2. EXIF details, confirm that statement.


    Notwithstanding those two points - the test was conducted over a period of only 2 minutes, and it is implied that the lighting did not change during that time.

    WW

  15. #15

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    Have a guess :)

    Re: False metering ?

    Hmmm - not an April Fool's joke by any chance?

  16. #16
    William W's Avatar
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    Re: False metering ?

    Quote Originally Posted by Colin Southern View Post
    Hmmm - not an April Fool's joke by any chance?
    I have thought of that possibility.
    If it is, then we will surely know: either by silence or by laughter.

    WW

  17. #17
    herbert's Avatar
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    Re: False metering ?

    Given the use of manual mode and shooting with raw I do not know how this has happened. If the image had been pushed 4 stops in post processing then we would see noise and banding artifacts.

    Try the test again but shoot at all single stop shutter speeds from your correct exposure down to your shutter limit:

    1/250
    1/500
    1/1000
    1/2000
    1/4000

    Perhaps you will be able to find out the shutter speed where the camera errors. If you do then repeat with all intermediate shutter speeds to see if there is a point at which the camera fails.

    Hopefully you will not be able to repeat the error and you can write it off as a mistake by the camera. If the error is repeatable then you may have a camera fault, or a combination of settings with a behaviour which we are not aware of.

    Alex

  18. #18
    William W's Avatar
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    Re: False metering ?

    Quote Originally Posted by herbert View Post
    Given the use of manual mode and shooting with raw I do not know how this has happened.
    Hmm, maybe I am misunderstanding the sandwich of three Images which was posted as the support document.
    I understood those three images to be the JPEG files, SOOC?


    WW

  19. #19

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    Re: False metering ?

    Yes and showing the similar camera settings

  20. #20

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    Re: False metering ?

    Alex,
    I have done all this now a couple of times without any aberration so it must have been a one-off fluke.
    Thanks guys

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