Metering

Discussion in 'Beyond the Basics' started by D40, Mar 12, 2008.

  1. D40

    D40 TPF Noob!

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    I hear a lot about setting the metering manually for say the background and locking it it but I do not understand what they are talking about? I am using the D40 so If anyone could explain what it is and how it works that would be great!
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    This is not something specific to the D40, or even digital cameras.

    Therefore there are plenty of great books, web sites and even posts on this forum that will help you out. You just have to look for them.
     
  3. jols

    jols TPF Noob!

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  4. nikonkev

    nikonkev TPF Noob!

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    Manually metering the background and using the AE lock button to lock in the exposure value is exactly what it is. For any reason, if you want to correctly, under, or over expose your background and lock in those values with your combinations of aperture and shutter speed, then you can. This would work to your advantage if you're using a flash and want to control your ambient light flow into your camera before you place a subject into your composition. Just a balancing act.

    Metering normally refers to the exposure of the picture - it's endogenous and determines how your final image will look. Your built-in metre will metre the frame according to shutter speed, aperture, and whatever EV you have it set to.

    Then there's the "type" of metering you choose to use to determine exposure of the frame/subject: matrix, centre-weighted, or spot, as what Nikon calls it.

    Read up on that - it's useful stuff.
     
  5. D40

    D40 TPF Noob!

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    So that is one reasone I am getting whight blown out backrounds when shooing oudoors? Thanks that was helpfull nikonkev!
     
  6. Seefutlung

    Seefutlung TPF Noob!

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    To be able to use Manual Metering to its fullest ... one must undertstand how the meter works. In a nutshell ... the meter is merely a guide for the photog to intrepret to his/her own advantage.

    1) the meter will give a proper exposure for an 18% gray (some are calibrated to 20%). 18% gray is halfway between white and black.

    Okay, so what does that mean ...

    If you point you camera at a black wall, center the needle, process and print without any manipulations and viola! ... your print will come out 18% gray. If you point your camera at a white wall ... et cetera ... you will end up with 18% gray print.

    The trick with metering is to meter off something which is 18% gray or meter off of something else which you select and adjust accordingly. So if you meter off something which is a bit lighter than 18% gray you will open up your aperture a bit (or lower your shutter speed) ... if you meter off something darker than 18% gray then you close down the aperture a bit ... if you meter off something more han a bit darker .. then you close down even more ... vice versa on the lighter end of the scale.

    If the background is lighter than the subject and you meter off the background then your subject will be under exposed ... if you meter off a background which is darker than your subject then your subject will be over exposed. If there is a moderate difference between the background and subject you can set your exposure somewhere between the two readings and be okay.

    Gary
     
  7. Helen B

    Helen B TPF Noob!

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    Here's a link to an earlier thread that explains something about the sort of tones that are similar to the mid-grey that meters are calibrated for. As already mentioned by Gary, the exact calibration varies a little - the reference is usually between 12.5% and 18% grey. Very early (ie about 1939) references were 14%, because that seemed to represent the average reflectance of an average scene.

    It may seem odd to say that 18% is mid-way between black and white but it is, in terms of human perception. We perceive a surface that reflects 18% of the light falling on it as being half way between black (about 3% to 5% reflectance) and white (about 90% to 98% reflectance), even though the true mix of half black and half white is much lighter - about 50% reflectance.

    Best,
    Helen
     
  8. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Keep in mind that there is a range of tones that you can capture in one exposure. If your subject is well exposed but your background is blown out...then the difference between the two, is just too much for your camera. You could meter for the background but then the subject (or foreground) would likely be too dark.

    This has always been a limitation of photographic mediums. Black & white film has a greater range and with careful developing/printing you can maximize the range. Color negative film has a pretty good range as well.

    Color slide film has less of a range, so you have to make more of a conscious decision about what you want to be exposed properly.

    You also might want to look into a spell checker :er:

    Digital sensors are getting better all the time, but from what I've heard...it's fairly close to slide film.

    Of course, as with B&W film & a dark room, digital images and computers make it possible (even easy) to adjust images to maximize your tonal range. It's even fairly easy to take multiple exposures and combine them into one image.
     

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