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I've found one suggestion about taking photo of sky:

The sky becomes white in ur photos unlike others who retain blue color?? - Stop down the aperture to f8 or more, decrease ISO to 100 and slower down the shutter speed to anything near 1/80th of a second.

The sensor in DSLR absorbs different spectrum of light at different rate. Blue is slowest. So you need to find ways to slower the shutter speed to a point in which lots of blue can be exposed on sensor..

Source https://www.facebook.com/D7100/posts/588610494525187

When I try to do some landscape photo, I often got overexposed sky, so it has a couple of huge white blocks. I thought that the problem is in too much difference between needed light for sky and ground. As I know that could be fixed by:

  1. HDR photo
  2. Graduated filter

But does this suggestion have sense at all? Does it helps in better landscape photo exposure?

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2  
What the!? I would be very wary anyway about any photographic advice that dispenses fixed exposure values for anything mote than a very specific situation. –  Itai Jul 20 '13 at 14:49
3  
No the suggestion does not make sense at all. The grammar in that post alone makes me cringe, they can't spell or use even close to proper English. I would suggest "unliking" or "unfollowing" that account on Facebook as it seems pretty obviously not owned by Nikon itself. Note - one does not "slower" shutter speeds. –  dpollitt Jul 20 '13 at 14:54
    
now I know that's useless suggestion. Thank you very much :) –  Sergey Litvinov Jul 20 '13 at 15:02
2  
Well, there actually is a grain of truth here. See photo.stackexchange.com/questions/10760/… But the bit about the sky becoming white seems mixed up, and the shutter speed recommendation shows lack of knowledge of how exposure works. –  mattdm Jul 20 '13 at 15:05
3  
I think the poor grammar in the quoted post is primarily due to cultural differences including learning English as a second language primarily online. Let's focus on the content rather than the delivery. –  mattdm Mar 25 at 10:57
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1 Answer

up vote 8 down vote accepted

It's utter poppycock, to be polite about it.

To be somewhat charitable to the author, our digital sensors do struggle just a little bit with blue at the current state of the art. But "not enough blue" is not the problem here.

To put it into some perspective, we can go back to the earliest days of photography, to a time when films were really only sensitive to blue and ultraviolet (or, as it was called at the time, "actinic light"). Landscape photographs of the period would almost always have uniform white skies, no matter what the weather was like, since the sky is very bright with a lot of blue content, and recording the landscape details meant recording the minuscule amount of blue light that would reflect from things that weren't the sky. (Water, of course, would often wash out completely because it was efficiently reflecting the sky above.)

More recently, panchromatic black and white film, which was also sensitive to red and green, would consistently record blank skies unless there was heavy, dark cloud cover. The way one got sky with gradients and clouds and so forth was to use a filter that would block the blue, or at least some portion of it. The most popular filters included the K2 yellow filter (which made things look "natural") and the #25 and #29 red filters (which made the sky dark and dramatic). Since clouds reflect the entire spectrum of light, including colours that were not being blocked by the band-stop filters, they would wind up lighter than the surrounding sky in the final image.

Colour doesn't change anything, except that we can no longer use band-stop filters to fix the bright-sky problem. Put a yellow filter on the lens and the blue goes away — not just in the sky, but everywhere. Needless to say (I hope), that will leave things that aren't the sky looking sort of funky. If there is enough blue recorded in the image to bring other things back to normal with an adjustment, then you're back to overexposed, washed-out skies again. (You can use a combination of a warming or narrow, near-UV-only bandstop filter and colour balance to reduce blue exposure somewhat at high altitudes with good effect, but that's only because of the additional UV and near-UV light at altitude, which will oversaturate the blue channel everywhere if you don't rein it in a little.)

The problem remains this: the sky is too bright compared to anything else. If you look at only the blue channel of the image, you'll see that there is plenty of blue recorded. The blue channel is probably completely saturated throughout most of the sky. You couldn't record more blue if you tried. Thing is, though, if you look at the red and green channels, you'll see that there's a lot recorded there as well. You'd expect that in the green channel, since the green channel is responsible for most of the luminance information in the image. But despite the heavy filtering making it sensitie mostly to the opposite end of the spectrum, the red channel is pretty much blown out in the sky as well. There is a lot of bright in the sky compared to the not-sky throughout most of the daylight hours.

To get a nice blue sky, then, the object of the game is to selectively underexpose the sky. There are a couple of ways we can do that at capture time.

Provided that you are not using a very wide-angle lens, a polarizing filter can be used effectively to darken the blue of the sky if the sunlight is coming in from the side-ish. This will not work if you are shooting into the sun or if the sun is at your back, since not enough of the light will be polarized in a way that lets you exclude it with a filter. And if you are using a wide-angle lens, the polarity of the light coming from the sky will be different enough across the image that you'll create unnatural gradients (left-to-right or vice versa, as opposed to the usual slightly curved top-to-bottom).

A split or graduated neutral density filter is useful provided that the horizon is not too complicated. Anything that sticks up into the sky will be selectively underexposed as well, and you may not be able to recover those details.

HDR, whether that's a continuous-tone image that's tone-mapped or simply two or more images selectively blended, lets you side-step the question altogether. You take a nice picture of the landscape, and you take a nice picture of the sky, then you glue them together somehow.

In all of these cases, though, the solution to the white sky problem is to cut the exposure of the sky. There is no way in the world that letting more light into the camera can making anything less white.

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Your answer is very useful for me. Thank you! –  Sergey Litvinov Mar 25 at 11:28
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