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Thread: Metering and exposure confusion

  1. #1
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    Default Metering and exposure confusion

    Hi all, I am new to photography and is always confused with metering and exposure compensation... appreciate all help rendered...

    1) Metering
    I am confused with the meaning of metering. Is metering a process in which the cam decides what settings to used to get the right exposure based on the spot/area metered?

    Is it right to say that in A mode, the cam decide the shutter speed and ISO based on this metering process?

    Suppose say i fix the aperture and shutter speed. Would metering off different area of the subject have a effect on the exposure?? Assuming ISO is also fixed at 100. In another words, if we control aperture, shutter speed and ISO, would metering have any effect??

    2) Exposure compensation
    Suppose say i have to fixed the shutter speed but can play around with the aperture. But at the max aperture size, my pic is still too dark. Would increasing the exposure compensation helps? Assuming ISO is also fixed at 100.

  2. #2
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    Default Re: Metering and exposure confusion

    1) Yes your def is accurate. Yup in A mode the camera decides everything. Its aim is to allow you to hand-hold the camera for all your shots regardless of the lighting condition.

    If you set your camera to Manual mode, metering will still be done. There's an indicator to tell you how far off your setting is from the ideal exposure metered by the camera. Or else how will you know if your setting's ok? Unless you're a) very very experienced b) using a light meter.


    2) No. In fact setting an EV value will have no effect, except on the recommended exposure of the camera. EV is only meaningful for Tv, Av, etc.

    To be more specific, in M mode, if you set an EV value, the camera will take this into account when determines ideal exposure. Its pointless cos you can alter you settings to give you the desired compensation yourself.

    In case you're wondering why I'm only taking about manual mode, its cos there's no way you can fix the shutter speed and alter aperture any other way.

    By the way EV is not D-lighting or safety flash or watever gimmick they wanna call their in-camera brightening routine. Its just a way for you to tell you camera to over or under expose when its in control over a either the shutter or aperture.

  3. #3

    Default Re: Metering and exposure confusion

    Quote Originally Posted by DaGimCi C0d3
    Is it right to say that in A mode, the cam decide the shutter speed and ISO based on this metering process?
    In Aperture priority, the cam decides the shutter speed based on the aperture AND ISO chosen. It doesnt choose an ISO for you. eg. for a given aperture size, a higher ISO chosen by you will result in faster shutter speed chosen by the cam and vice versa.

    Quote Originally Posted by DaGimCi C0d3
    Suppose say i fix the aperture and shutter speed. Would metering off different area of the subject have a effect on the exposure?? Assuming ISO is also fixed at 100. In another words, if we control aperture, shutter speed and ISO, would metering have any effect??
    I'm assuming you are shooting in manual mode. After you have decided on an ISO, aperture size and shutter speed, camera metering will display the exposure level of the selected point of focus.

    You will have to adjust the aperture size/shutter speed/iso accordinging to the displayed exposure.

    eg. when shooting your dog at iso 200 1/40 F/5.6 and the meter shows the exposure as underexposed, u can either bump up iso, decrease shutter speed or increase aperture size to obtain the correct exposure

    This is purely from my understanding. Dont crucify me if I have my facts wrong

  4. #4
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    Default Re: Metering and exposure confusion

    Just to clarify... does your A mode refer to Aperture priority or full-auto.

    I usually take A to mean full auto since I use canon... but I know that nikon uses A to represent Av... didn't state what camera you're using to I assumed you're referring to auto.

  5. #5
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    Default Re: Metering and exposure confusion

    Quote Originally Posted by solarii
    Just to clarify... does your A mode refer to Aperture priority or full-auto.

    I usually take A to mean full auto since I use canon... but I know that nikon uses A to represent Av... didn't state what camera you're using to I assumed you're referring to auto.
    sorry for the confusion... my A refers to Av (Aperture priority)... still trying to absorb and understand what is written here...

  6. #6

    Default Re: Metering and exposure confusion

    Quote Originally Posted by DaGimCi C0d3

    1) Metering


    Suppose say i fix the aperture and shutter speed. Would metering off different area of the subject have a effect on the exposure?? Assuming ISO is also fixed at 100. In another words, if we control aperture, shutter speed and ISO, would metering have any effect??
    once u fix ISO, aperture and shutter speed, the camera will expose for the scene at that fixed values regardless of the metered value

    ie u are actually shooting manually already

    Quote Originally Posted by DaGimCi C0d3

    2) Exposure compensation
    Suppose say i have to fixed the shutter speed but can play around with the aperture. But at the max aperture size, my pic is still too dark. Would increasing the exposure compensation helps? Assuming ISO is also fixed at 100.
    yes

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    Default Re: Metering and exposure confusion

    Bro, I will explain everything here and hope you are able to grasp what exposure is all about.

    Firstly, when taking metering, always aim your camera at something that is closest to medium grey colour. Metering off too light or dark colours will fool your camera's meter and result in over or under-exposed shots.

    ISO: This is always chosen by you. Determined by how fine you want your images or how 'noisy' or pixelated you want them. Though at most times fine images are required, there are certain subject matter that look better grainy.

    Aperture Priority: This means you set the aperture you want while the camera finds a corresponding shutter speed that gives the correct exposure.
    This is used primarily when you require control over the Depth-of-Field. In other words you need to control how sharp or blur the background is.

    Shutters Priority: This means you set the shutter speed you want while the camera finds a corresponding aperture that gives the correct exposure.
    This is used primarily when you need to 'freeze' movement or show blur with movement.

    Manual Mode: Many photographers, myself included, like total control. You get full control in manual mode, meaning you select the shutter and aperture. Of course this has to dialed in with the help of the camera's meter or an external Light/ Flash Meter.
    Last edited by Heartshape; 13th February 2006 at 06:02 AM.

  8. #8
    Senior Member yyD70S's Avatar
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    Default Re: Metering and exposure confusion

    Don't know if it's relevant to you but this is a good reference 'starter kit' with regard to exposure.

  9. #9

    Default Re: Metering and exposure confusion

    Quote Originally Posted by yyD70S
    Don't know if it's relevant to you but this is a good reference 'starter kit' with regard to exposure.
    where's the reference?

  10. #10
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    Default Re: Metering and exposure confusion

    Perhaps you wanna read up on Ansel Adam's "The Negative".

    I saw one at the National Lib (Taka). Seems to be always there....

  11. #11

    Default Re: Metering and exposure confusion

    Quote Originally Posted by DaGimCi C0d3
    Hi all, I am new to photography and is always confused with metering and exposure compensation... appreciate all help rendered...

    1) Metering
    I am confused with the meaning of metering. Is metering a process in which the cam decides what settings to used to get the right exposure based on the spot/area metered?

    Is it right to say that in A mode, the cam decide the shutter speed and ISO based on this metering process?

    Suppose say i fix the aperture and shutter speed. Would metering off different area of the subject have a effect on the exposure?? Assuming ISO is also fixed at 100. In another words, if we control aperture, shutter speed and ISO, would metering have any effect??

    2) Exposure compensation
    Suppose say i have to fixed the shutter speed but can play around with the aperture. But at the max aperture size, my pic is still too dark. Would increasing the exposure compensation helps? Assuming ISO is also fixed at 100.
    Read the following link below and understand fully and you would get the answers. Once you have an idea of how the camera "measure the light condition" based on the metering method chosen by the photographer and then automatically set aperture and/or shutter speed and/or ISO (depending on the mode (A, S, P used) to get what it thinks it's a "proper" exposure (where the exposure meter is centred as zero), then you would also understand what exposure compensation is all about (asking the camera to automatically set the aperture and/or shutter and/or ISO to let in more or less light than what is the "proper" exposure as determined earlier by the metering method chosen).

    Indirectly, it also means that if you're using full manual control (i.e. you set the aperture, shutter speed and ISO youself instead of letting the camera set any of those for you automatically), exposure compensation has no effects on the exposure except changing where the exposure meter show as zero value (i.e. what the camera think is the new proper exposure after taking into account the value you've set in exposure compensation).


    http://www.shortcourses.com/using/exposure/chapter3.htm

  12. #12
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    Default Re: Metering and exposure confusion

    Hopefully this will reduce the confusion somewhat.
    Metering basically means the measuring of light by the device, be it a handheld meter or the camera's built in meter (in your case, the camera).
    When you use the auto, aperture priority, shutter priority or any of the other modes eg. party, portrait etc, you are letting the camera decide on the camera settings based on its own metering. However, when fixing both the aperture and shutter speed ie. in manual mode, you can still see the camera metering working. Ie. your camera will still tell you if there will be over or under exposure, though you can still choose to ignore it.

    As for exposure compensation, it is a way to calibrate your camera's metering sensor. Eg. if your camera is constantly overexposing your pictures in the auto mode, you can set the exposure compensation on your camera to underexpose by the same amount thereby tricking your camera into thinking that the pic is not as dark as it thinks. Ie. you are compensating for your camera's metering inaccuracy.
    As for trying to exceed the physical limits of your camera using this function, like trying to capture a correctly exposed picture once you have maxed out on the shutterspeed and aperture and even the iso setting, is an impossibility.
    Last edited by MDZ2; 15th February 2006 at 12:37 PM.

  13. #13
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    Default Re: Metering and exposure confusion

    A big THANKS for everyone that contributed to this thread.

    I shall close the thread for now...

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