Judging Exposure Confusion

Discussion in 'Photography Beginners' Forum' started by weepete, Jul 3, 2013.

  1. weepete

    weepete TPF Supporters Supporting Member

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    Hi all,

    I've heard said a few times now that you should never judge the exposure by using the LCD screen on the back of the camera, but this has got me a bit confused. Given that a histogram is just the graphical representation of the value of the pixels for that image really the only thing it can tell me is whither I've clipped the shadows or highlights. I could in theory take a picture with a normal looking histogram, no clipping, in which the subject could be exposed incorrectly. Add to this the fact that the in camera meter not allways right and can also produce a picture in which the subject is not properly exposed.

    So if I can't trust the camera meter, can't tell from the histogram and not supposed to use the LCD how on earth am I meant to judge the correct exposure in camera?
     
  2. gsgary

    gsgary Been spending a lot of time on here!

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    Hand held meter, i allways carry one even shooting digital
     
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  3. cgipson1

    cgipson1 TPF Noob!

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    The meter is OK... and will always give a reading! With experience, you will know how to integrate the meter reading with the subject /foreground / background to get the exposure you want. A lot depends on how you meter (single point, wide matrix, etc...).

    If you have a white subject (SNOW?), the meter will try to make it gray (12% or 18%)... and it is up to you to know that you need to overexpose that subject 1.5 to 2 stops. The meter read it correctly... the meter just doesn't read white... it reads gray.

    If you have a very contrasty subject... you may need to pick where and what you want to meter (at 12% or 18% gray) to properly expose what you want exposed... not what the camera GUESSES you want exposed.

    In my opinion, if properly used... you can almost always trust the camera meter. And the histogram is what will confirm that. (but don't trust the LCD)

    Some useful reading on Histgrams:

    http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

    http://digital-photography-school.com/how-to-read-and-use-histograms
     
    Last edited: Jul 3, 2013
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  4. amolitor

    amolitor TPF Noob!

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    The LCD screen is very hard to read properly. Mine, for instance, happens to render pictures as if they have rather more exposure than they do. If I am eyeballing by LCD, I need it to look substantially OVER exposed on the back of the camera, for the shot to be exposed right. At least some of this depends on how you have set your camera up (you can probably adjust the degree of LCD backlight) and what the ambient lighting conditions are. I have not investigated because I don't much care, but I suspect that I have the backlight turned up quite high, which makes the LCD rendering appear much brighter than the actual picture is.

    The histogram gives additional information, as you stated it tells you about clipping, but it also gives you a rough idea of how the tones look overall.

    The histogram needs to be looked at in the context of what you're shooting, though. If you're shooting a dark mass with a few bright things in it, you might get two lumps on the histogram, a big one for "most of the frame" down toward the bottom, and a smaller one up toward the top for the "little bright things".

    A more normal scene will be one big wide lump which should be centered, or if you prefer, placed as far to the right as possible without clipping.

    The meter provides yet more different information, depending on how you use it. You can spot meter bits and pieces of your scene, and set exposure accordingly.

    There's a lot of stuff in play. It's really almost surprising how often just doing what the meter tells you will produce pretty much what you want.
     
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  5. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Then you're not interpreting the histogram correctly.
     
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  6. KmH

    KmH Helping photographers learn to fish Supporting Member

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    To consistently make high quality digital images requires obtaining a good fundamental understanding of how digital images are made so you can control the process.
    In the days of film, the lab that developed the film handled most of that for the photographer. Today's digital photographer has to have that knowledge, because so much of the image development process is now done in the camera.

    There is no normal looking histogram. Scene content determines what should be 'normal'.
    A accurate exposure of a white dog on a snow covered field will produce a very different histogram than the histogram of an accurate exposure of a black dog on an asphalt parking lot.

    The rear LCD view of a photo can't be used to accurately judge exposure because:
    1. It isn't a calibrated display, and can't be calibrated.
    2. It can only show a JPEG thumbnail.
    3. The ambient light falling on it is inconsistent, which impacts how it displays an image.

    Understanding Digital Camera Histograms: Tones and Contrast
    Understanding Digital Camera Histograms: Luminosity and Color
    Optimizing Exposure
    ETTR
    http://wwwimages.adobe.com/www.adob...e/en/products/photoshop/pdfs/linear_gamma.pdf
     
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  7. KenC

    KenC Been spending a lot of time on here!

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    With experience the histogram will tell you what you need to know. Until then, you do the best you can with it and whatever info you can get from the displayed jpg.
     
  8. Dao

    Dao No longer a newbie, moving up!

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    I sometimes use spot meter and point it to an area where I think the camera can get me a correct exposure and then press the exposure lock button.

    i.e.
    Pointing at the human face/skin.
    Pointing at the grass.
    Pointing at the grey colour object.

    And definitely not black or white.
     
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  9. cgipson1

    cgipson1 TPF Noob!

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    Black and White is fine... (and sometimes a good point to judge from), as long as you dial in proper EC.
     
  10. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Spot metering the brightest and the darkest parts will give you the dynamic range of the scene. This is valuable in comparing to the dynamic range your camera is capable of.
     
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  11. hirejn

    hirejn No longer a newbie, moving up!

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    You can trust the camera meter 100% -- to expose every subject for 18% gray. Easier said than done, which is why I prefer an incident meter.

    The LCD got a bad rap probably from the early days when it might not have been accurate. With new cameras, some of the LCDs are even calibrated for accuracy, and many pros judge lighting by the LCD, so the notion that the LCD is useless is garbage. If the brightness is set to neutral, in many instances a quick look at the LCD gets you in the ballpark. So the answer is you can use the LCD as a confirmation of informed exposure. But if you don't know how to expose and the LCD is max brightness, then you're guessing.

    I think not understanding exposure is a big reason people have problems with the LCD and historgram: They use those tools to make an exposure instead of the right tool -- their brains. If you simply let the meter tell you what to do, then you're not really making an informed exposure and therefore you won't be able to predict what the shot should look like. But if you have a system and understand it, you will know before you take the shot what it should look like, and thus the LCD will be a good confirmation. With experience, you can use the review to make a quick adjustment and know you got it. If you don't understand exposure or don't use an incident meter, you can't do this.

    The histogram also gets a bad rap. The problem with a histogram is you don't know what a histogram should look like. Every shot is different. A low key shot will have the histogram more to the left and it will look underexposed but will be accurate for the shot. But it's a valuable tool. If you already know how to meter and expose, the histogram is a better blinky. The blinkies tell me only whether highlights are blown out, not by how much, so for me the histogram has an advantage. It tells me how much the highlights are blown out, and I can make a quick adjustment. Even when incident metering, the reading can be off by a third stop, so a quick check of the histogram confirms that I have detail in the highlights.

    The other problem with blinkies is if they're not blinking, you can't just assume the exposure is perfect. Again the historgram tells me how much detail is in the highlights, and it might be too much. For example, the histogram might go no further than the center, but I know the scene has highlights so it should be further right. The blinkies can't tell you this. The histo is also an essential for "shooting to the right," or maximizing highlight detail. For anything other than highlights or shadows, the histogram is not practical to decipher accurately. It's one more tool that can help you see how close your exposure is, but it doesn't do everything. Some people hate it but I have a way of using it that helps me.

    So, the only way to know is to use an incident meter or have a lot of experience with reflective metering. The LCD, blinkies and historgram are just tools to help you gauge exposure. They are not tools by which to begin an exposure. In reality, with today's RAW files and software, being off by a half stop isn't huge. Being off by a third is nothing because a slight tilt of the incident meter can do that, and the meter could be off by a 10th of a stop from a given reading. If you're off by more than half, then you need to get better at metering and exposure because there's no sense fixing stuff when you can do it right in camera. The closer you are, the more time you save in post.
     
    Last edited: Jul 3, 2013
  12. candidchick

    candidchick TPF Noob!

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    Sounds like you are little more inexperience when it comes to histograms and metering, and that's why you are here. I understand its frustrating and confusing. I myself have been learning more and more about it too, as I am doing photography classes and have to meter and use histograms to get the exposure. I would suggest in investing in a 18% gray card, and they're really cheap on Amazon. Zooming in onto the gray card and metering off it will help with exposures, and to know weather to overexpose or underexpose but one or two stops, like on snow, or if its just right when you do meter and adjust the settings. Light meters help also but those can be on the pricey side. Bracketing is your friend and that's what people use to do with film cameras. (bracketing is a technique of taking several shots of the same subject using different settings aka exposures)
     
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