light reading help

Discussion in 'Photography Beginners' Forum' started by voodoo_child, Sep 5, 2006.

  1. voodoo_child

    voodoo_child TPF Noob!

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    So I've been learning from the book "Understanding Exposure" for a few days now but there are a few things that still arent clear to me. I understand the use of aperture (depth of field) and shutter speed (motion effects) and correct exposure.
    The problem for me is taking a light reading to create a correct exposure. Where do I take the reading from? I know this is completely different for every situation so I will give some examples.

    In each of these pictures can you tell me where the reading was taken and why?

    1
    http://img438.imageshack.us/img438/6627/1eh8.jpg
    2
    http://img451.imageshack.us/img451/3726/2id6.jpg
    3
    http://img436.imageshack.us/img436/1650/3kz9.jpg
    4
    http://img451.imageshack.us/img451/1761/4jw6.jpg

    the last one is from bryan peterson's book the others I just collected over the months since I got broadband.

    BTW im using an olympus OM2, the manual says it has "TTL direct 'OTF' light metering" if it makes any difference.
     
  2. Digital Matt

    Digital Matt alter ego: Analog Matt

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    Nobody except the photographer can tell you where they metered. I can tell you what I would look for, depending on the medium you are using. If you are shooting negative film, I would expose for the shadows. Keep in mind that your meter defaults to 18% grey. Point your camera at the darkest shadow that you want to reproduce. Make this area 2 stops below what the meter says (otherwise the meter would try to render this deep shadow as a medium grey). Bracket to make sure you are getting a good exposure. (vary the exposure over and under the given reading).

    If you are shooting slide film (positive), or digital, you should expose for the highlights. Find the brightest highlight in your scene, and base your exposure off of that. Some people even underexpose by 1/2 a stop for more saturation.

    Keep in mind, every situation is different, and this is only a general guideline. Also, this is assuming some kind of spot or center weighted average metering. If you are using an average, or matrix metering, you would just compose your scene and meter, as the meter takes the whole scene and averages it. TTL is "through the lens" and OTF is "off the film plane". You should still have different metering patterns to choose from however.
     
  3. voodoo_child

    voodoo_child TPF Noob!

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    Very confused right now!
    After reading some articles online, most say to expose for the subject, your saying expose for the shadows and the book says if there is a sky in the frame always expose for that(the sky brothers!). :confused:

    I've borrowed quite a few beginners photography books and this subject has not really been explained in much detail in any of them.
    Its time for me to just go out and experiment. (I hate having to wait weeks to see the results though)
     
  4. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    As DMatt said, there are almost as many ways to meter as there are photographers.

    You need to know the metering pattern of your in-camera meter. Is it reading just out of the center? Is it averaging the whole scene? Is it a segmented pattern?

    The meter is giving you an exposure recommendation that will result in a tonality of middle gray. If you meter something dark/black, it tells you how to get gray. If you meter something light/white, it tells you how to get gray. If you meter something in the middle/gray, it tells you how to get gray.

    First you have to decide what "correct" exposure is, and only you can decide that. For instance is the correct exposure of palm trees in a beach scene to get full detail of the bark of the trees? Or is it to get full color in the sky, and have the trees come out as solid black silhouettes? Or something in between?

    A common strategy is to meter the most important part of the scene. Now if that important part isn't middle gray, and you want it to come out with a similar tonality as it has in reality, you have to remember to compensate. If it's dark, then under expose from the meter's recommendation (going from gray to darker). If it's bright, then over expose from the meter's recommendation (going from gray to brighter).

    For negative film you are usually worried about losing shadow detail, so you meter the important shadow area, and underexpose two stops from what the meter recommends. For positive film and digital you are usually worried about losing highlight detail, so meter the important highlights, and over-expose a stop or two.

    With digital, you can then check the histogram to see what your distibution of tones is, and adjust the exposure accordingly. The learning process with film takes longer of course, since you have to process it to see what you got.
     
  5. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    You might find it useful to invest in a gray card (they are cheap). Place the gray card in the same light as the subject you are metering, and compare the recommendations the meter gives you for the card and the subject. This will help you learn how to estimate tonality of colored objects. For instance I know that a healthy, green lawn is about the same tonality as middle gray, and the palm of my hand is one stop brighter than middle gray.
     
  6. Rob

    Rob TPF Noob!

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    I'll have a couple of guesses on your question, based on what I'd do in those situations:

    1. Tricky... I'd probably set the camera in matrix metering mode or the widest CWA mode and let it figure it out. A scene like that doesn't actually have too much in the way of shadow or highlight detail, it's relatively even, so pick the bit that's most important - the sky? the sea? the beach?

    2. This picture looks fake to me. I'd say that a heavy blue filter has been applied to the sky (the clouds are blue) in photoshop. I'd personally say that the metering was probably off the road in this shot though. Or the same as #1.

    3. Easy, the subject. Again, I'd say the bg had been manipulated, but this is a classic meter on the subject situation.

    4. Same as 3, I'd bet the leaves of the flowers were the meter subject.


    Hope this helps, it's pure speculation though!

    Rob
     
  7. Torus34

    Torus34 No longer a newbie, moving up!

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    It might help [and it might not!] to think of the 'correct' exposure using the concept of 'zones', or narrow ranges of densities or 'grays.' How wide are these zones? Well, if you double the shutter speed [eg, from 1/250 to 1/500] or reduce the aperture by one full f stop [f8 to f11], you have moved the exposure one full zone. If you cut the shutter speed in half [eg, 1/250 to 1/125] or increase the aperture by one full f stop [f8 to f5.6], you've moved one full zone in the opposite direction.

    Read that paragraph again to be sure you've got it before continuing.

    Next, think of b&w film. [Yes, I know you shoot color film, but thinking in b&w makes the following a bit easier to understand.] B&w film records shades of gray. Now think of it as recording zones of grays. In general, a properly exposed and developed b&w film can record a total of 9 zones of grays. Let's call them zones 1 through 9. The zone at one end is almost black. The zone at the other end is almost white. The zones from 1 to 9 form a 'scale' of grays.*

    OK, here comes a change-up pitch! Right smack center in the middle zone, Zone 5, you'll find the same shade of gray as that on an 18% gray card.** So whenever you read about a meter trying to record something as 18% gray, the meter is simply trying to set an exposure safely in the exact middle of the range that the film can record. It's also why you can use an 18% gray card to determine an exposure for a scene containing a whole range of grays [zones].

    Now let's wrap this puppy up and go home.

    The deep grays at one end of the scale are those of the shadows. The light grays at the other end are those of the highlights.

    In a scene where the range of grays, from the deepest shadows to the brightest highlights, does not exceed 9 zones [or 9 f stops, or 9 shutter speeds -- it's the same thing***], you set your exposure for zone 5 -- 18% gray. Your film will capture the full range of grays.

    On an overcast day, when there's less contrast, the full range of grays in a scene may be less than 9 zones. Let's say that it's only 7 zones. The same procedure applies here also. The safe spot is 18% gray -- zone 5. You've got a safety zone [Sorry!] at each end of the scale.

    However, and this is one big however, if the range of grays exceeds 9 zones [bright sunlight on snow with deep shadows under fir trees], you have to make a choice on which zones you choose to lose. You can reduce the exposure [faster shutter or smaller aperture] and have a better chance of capturing detail in the snow [Deepest shadows will go completely black - no detail,] or you can increase the exposure [slow the shutter down or open up the aperture] and have a better chance of capturing detail in the shadows [Snow will go blank white - no detail.]

    When you've got the time to do so, you can meter the shadows, meter the highlights, and then decide on your exposure. [This is where a hand-held meter comes in -- especially if you've got your camera set up on a tripod!] If the range is 9 zones or less, go for the middle zone. If the range is greater than 9 zones, make your choice on what you are willing to lose. Not sure? Take multiple exposures, each separated by a zone [This is called 'bracketing' an exposure.]

    If you don't know the reading for the deepest shadow and brightest highlight, you go with a 'best guess.' It's important then to know how your camera's exposure meter 'sees' the scene. Past experience with similar situations is also important. Chances are, and I haven't checked this, the OM2 tends to read the center of the scene.

    It's time now to make a visual adjustment to your thinking. The real world is in color, not b&w. [Yup, I knew that all along!] You will have to look at a scene in terms of the brightness or darkness of the colors to determine the 'shadows' and 'highlights.' The deepest, most saturated colors in the lowest light are shadows. The least saturated colors [nearest to white] in the brightest light are the highlights. Color films differ from b&w in the number of zones they can capture. I'll leave it to you to find out about your particular film. This doesn't change a thing. You still go for the center zone unless the range of brightness in a scene exceeds the film's capabilities.

    Believe it or not, with time this sort of thinking becomes an almost automatic process.

    *You'll note I haven't said which end is which! That's because the zone which is lightest on a negative forms the darkest image on the print. You've got enough on your plate right now without trying to keep that all neat and tidy in your mind!

    **Thinking of 18% gray as the middle is no stranger than thinking of middle C on a keyboard. The center of the scale is D, not C. In school, C is considered as a middle grade, but C is only the third letter in a 26 letter alphabet.

    *** The ISO film rating system is also in zones, if you wish to think of it that way. Go from an ISO50 to an ISO100 film and you can capture one more zone toward the dark end at the same exposure. ISO numbers double for each increase in zone - 50,100,200,400,800, etc. From ISO50 to ISO400 is a shift of 3 'zones.'
     
  8. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Google "zone system", and you'll come up with hundreds of sites that demonstrate this with visual examples.
     
  9. voodoo_child

    voodoo_child TPF Noob!

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    After reading an article on the zone system all of the above posts are making a lot more sense to me.

    Thanks for all the helpful replies, this forum is turning out to be a great learning resource.
     
  10. Naturegirl

    Naturegirl TPF Noob!

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    This is, by far, the most helpful & detailed explanation I've ever read. :thumbup:
     

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