Why sky over exposed

Discussion in 'Photography Beginners' Forum' started by adikrist, Jul 30, 2010.

  1. adikrist

    adikrist TPF Noob!

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    Hi, I am a beginner in photography and i'd like to know what is the reason that the sky is over exposed in my photos.
    I know this is quite a common problem. Found some infos in google, but they all saying about how to fix over exposed sky and how to avoid it.. But what is actually the reason that this happens?

    Thanks for tips..
     
  2. JasonLambert

    JasonLambert TPF Noob!

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    When you point the camera at your subject it is taking the light meter from the subject and not the sky. Point the camera at the sky and you will see your subject get dark.
     
  3. Robin Usagani

    Robin Usagani Been spending a lot of time on here!

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    Thats why people often meter the sky and use flash.
     
  4. adikrist

    adikrist TPF Noob!

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    Thank for quick reply.

    @Jason: if i point the camera on the sky, the subject will be blur as it's not focused.. ?
    @Schwettylens: i dont like the effect using flash as the face will look somehow shinny. Any other trick besides using flash?
     
  5. Robin Usagani

    Robin Usagani Been spending a lot of time on here!

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    Flash with diffuser
     
  6. PJL

    PJL TPF Noob!

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    What are you trying to take pictures of? If you're doing landscapes, then the simple solution is a graduated neutral density filter; they're tinted on top and fade to clear on the bottom, so you can lower the brightness of the sky by a certain number of stops and correctly expose the foreground.

    Shiny faces shouldn't be a problem if you use a fractional power setting on an external flash. It's possible on most external flashes with some manual control to go to 1/2 power or 1/8 power for fill-flash purposes. You can also use a flash diffuser, which is a piece of opaque plastic that attaches to the front of the flash. If you're using on-camera flash, try a piece of tissue paper (or two) taped over the flash to soften it. You should also check on your particular camera model. My Elan 7, for example, automatically assumes the flash will be the primary source of light in P mode and sets the exposure accordingly. In Av mode, however, it assumes the on-camera flash will be a fill flash and sets the exposure as if there were no flash involved.
    This isn't that hard to overcome. Some cameras have exposure lock, where you can meter off one thing, lock in that exposure, and then recompose your shot. Or, if you shoot in manual using your camera's light meter as your guide, set your shutter and aperture to correctly expose the sky, then recompose your picture without changing your shutter or aperture settings. That being said, without a flash it's likely that your subject will come out underexposed.
     
  7. Robin Usagani

    Robin Usagani Been spending a lot of time on here!

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    You still want to focus on the subject.. but use the shutter speed if you were pointing it to the sky.
     
  8. JasonLambert

    JasonLambert TPF Noob!

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    I was just stating this to show the exposure difference. You asked "Why" it was happening.
     
  9. pgriz

    pgriz Been spending a lot of time on here!

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    It happens because your digital camera has a limited dynamic range. Usually (but it depends on the camera), the camera can handle 4 stops of exposure (over and under) and still show some detail (ie a dynamic range of 8 stops). Outside of that, things are either white (completely overexposed) or black (completely underexposed). Some films have a greater dynamic range (10 or even more stops of exposure, depending on the processing).

    If you meter the sky and it is 3 stops (or less) brighter than your main subject, you will get some sky detail. 4 stop or more, and you'll be getting white. So if you want detail in both the sky and your subject, you either lower the sky brightness (by using a graduated neutral density filter), or you adjust your exposure so that both the sky and subject fit within the dynamic range of your camera, or you brighten up your subject using a fill light or flash.
     
  10. Dao

    Dao No longer a newbie, moving up!

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    First, you may need to know that image recording mediums have a limited dynamic range (luminance range) that they can capture.

    So when you try to capture a scene where the luminance range between the brightest point (such as the sky) and the darkest point (such as shadow of the tree) is too high that your recording medium (such as image sensor or film) cannot cover the entire range.

    So if your camera meter the lower range, so it can capture all the details about the lower range (i.e. different level of shades), however, you will lose all the details on the upper range. So anything beyond the upper range will have the same luminous. (Or what people usually refer as blown out).

    Of course, if you meter the sky, your camera will capture the details on the upper range, but the details on the lower range will have the same value. So you may not able to tell if that is a leaf or a shadow of the leaf since they both black.

    Now, how to solve the problem. It really depends on situation. If you are taking a photo of a person or an object and that subject is close by, you can use a flash, a light reflector to light up the subject so that the camera can capture the entire luminance range of the scene.

    What if you are taking a landscape photo, the graduated neutral density filter may help. Or you can bracket the shots (taking multiple photos of the same scene with different exposure settings) and merge them in post processing.

    Or take the photo at a different time when sun is not right above your head :)
     
  11. bigtwinky

    bigtwinky No longer a newbie, moving up!

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    Great post pgriz.

    To add on to it...your meter in the camera is trying to adjust the light to get the exposure to an 18% grey level. Picture a ruler where you have black on one end, 18% grey right in the middle, and white on the other end. The 18% grey is the nice middle point for an exposure.

    If you have a scene where the sky is bright and the foreground is dark, and you meter the sky (thus telling the camera that you want the sky to be well exposed), what the camera needs to do is bring down the exposure to get the sky nice and exposed. However, any adjustment to exposure the camera does applies to the entire image. So as the exposure goes down to make the sky nice, it also goes down to make the foreground even darker.

    On the flip side, if you meter off the foreground (thus telling the camera that you want the foreground to be well exposed), the meter will see that is is dark and then will brighten the exposure to bring it from the black to the 18% grey. But again, by making the foreground brighter, it will also brighten the sky, which is already bright. So you end up with a nicely exposed foreground and a blown out sky.

    So in other words, the dynamic range is too great for the camera to fully exposure the entire scene properly. The human eye is way more advanced than a camera lens, which is why we see things properly. Although if you stare at a bright sky for a while and then look at a dark, shaded area, you will first see only black and then your eye will adjust and brighten the black giving you more detail. So even the human eye has its limitations.

    Funny thing... why did pirates where eye patches? Not because they had one bad eye. They often had eye patches on one eye to keep that eye in constant dark. As pirates would go from above deck where it is really bright to below deck where it is really dark, they would not want to wait for their eyes to adjust. So when they would go below deck, they would switch the eye patch to the other eye, so their eye that was covered, which is already in the dark, will pick up detail in the dark much quicker.

    Ok... back to the topic...

    How to fix the scene?
    - this is where HDR often comes in. HDR stands for High Dynamic Range. What you essentially do is take 3 (or more) images, one in the middle exposure, one that is over exposed (giving you foreground detail but a blown out sky) and one that is underexposed (giving you detail in the sky, but a foreground that is all black). You then merge these images in an HDR software (Photomatix or PS) and adjust.

    - use flash. If you have a person as a subject, then you can expose for the sky (making the person dark) but then use the flash to light the person. Works on people, but if you are doing a big street scene with a bright sky, you can't really light the entire street (well, you technically can, but good luck finding all those lights)

    - think if you really need the sky or the foreground in the image and adjust your shooting angle. Adjusting your angle will minimize the really white or really dark parts of the scene.

    Hope this helps...
     
  12. adikrist

    adikrist TPF Noob!

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    Thank you guys!! Very useful tips.... will pay attention next time.
     

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