Blue skies look grey

Discussion in 'Canon EOS' started by hector_evans, Apr 10, 2008.

  1. I noticed than when I shoot in bright sunlight the blue sky looks grey in my
    shots. I cannot fully fix this in Digital Photo Professional. I suspect that
    this has to do with the small apertures (f18-f22) I use in bright sunlight
    conditions. Any suggestions on how to get the correct colors? I have a Rebel
    XTi, using manual mode.

    thanks
     
  2. Example or it didn't happen! You don't mean overexposure, do you?
     
  3. Hector,


    Could you post a sample image?


    Antonio
     
  4. white-grey or just grey?

    If you are shooting in the general direction of the sun on a clear day, unless the sky is bullet blue, it's likely you are overexposing the sky. Especially if there is any pollution or haze (not that we have any of that in north america).

    A polarizer can help quite a bit (only at certain angles to the sun), but you will likely just have to either shoot with the sun at your side/back, or underexpose the foreground to make up for it. Fill flash helps for closer subjects, a neutral gradient filter works great for landscapes to dial down the sky a few notches.

    Remember, a digital camera doesn't have the same dynamic range that your eyes do... so when you are shooting something that is in shadow on a bright day will render everything that isn't in shadow, well overexposed.

    Also, you are going to be better off shooting at f8 or f11 max. There is no advantage to ultra high apertures on a crop sensor (you don't gain any sharpness) and you introduce some pretty substantial diffraction problems that can soften the center substantially.

    In bright sunlight, try shooting at f/11, ISO 100 and 1/250. Try using a polarizer, and do your best to position yourself so you arn't shooting directly into the sun.
     
  5. It's hard for a camera to expose for shaded foliage and bright sunlight at the same time. Lower the exposure compensation to -2/3 and take the picture again. Then use Photo Shop to get the photo you want.
     
  6. Just an aside - generally avoid those small f/18-f/22 apertures on your crop sensor
    camera. You are compromising the potential sharpness of your images by introducing
    diffraction blur.

    Unless you have a very good reason in a particular shot for using a smaller aperture, stick
    to about f/8 or larger.

    And do share a sample or two of your problem shots so that we can more effectively offer
    advice.

    Dan
     
  7. One more approach, if this is a controlled shot, would be to make two exposures. One for the sky and one for the foreground. And blend them in photoshop later. But obviously this can't work with action photos, only scenics.

    Underexposing, tweaking later, and fill flash can all help. But for extreame cases, your best bet is slow colornegative film, which is why I kept my EOS 1 and keep it handy.
     
  8. If you are shooting with a crop sensor body at those apertures you will definitely be seeing
    the effects of diffraction (loss of fine detail, lack of sharpness).

    I am guessing you are exposing for a dark foreground and the sky is getting blown out. A
    polarizer could help depending on the angle of the sun, or a graduated or split ND filter
    may be the answer. Posting an image would definitely help people give you relevant advice
    though.
     
  9. zml

    zml

    If you are shooting with a crop sensor body at those apertures you will definitely be seeing the effects of diffraction (loss of fine detail, lack of sharpness).

    That thing again..? In real life - pictures of resolution charts excluded - you are losing more detail and sharpness due to poor technique (both shooting and post-processing) than due to lens diffraction (or the diffraction-limited sensors, whichever way you prefer to nitpick.)
     
  10. Most has been said, sun behind reflects blue in sky, stick around f8 etc. here`s a simple tutorial to help fix pics that you want more blue in the skies

    http://www.myjanee.com/tuts/adjlay/adjlay.htm

    have fun :)
     
  11. "That thing" is very real, very noticeable, and if your technique and post processing are
    worse than bad diffraction then there are some real issues.

    I would advise reading this tutorial to understand the physics, and look closely at the
    fabric sample illustrated to see the very real effects.

    http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm#

    Many overzealous photographers looking for ultimate depth of field, have ended up with
    distinctly fuzzy shots, purely through stopping down too far for the format.

    Seriously, this is a "real life" issue and at f22 on a 1.6X crop camera you WILL see it - and
    yes, that IS poor technique.
     
  12. zml

    zml

    that IS poor technique.

    No, that is pixel-peeping.
    You'd be hard pressed to detect any artifacts of diffraction in most real life pictures taken above the "theoretical" threshold of diffraction-limitation of a given sensor (say, above f/9-10 for a 1.6 crop.)
    And yes, I'm very familiar with the science behind diffraction and am not denying it; I'am merely stating that diffraction is like bacteria: it's there, but hard to actually see without unnatural devices.
     
  13. I have seen the effects of diffraction in medium format and even 4x5 Polaroids of studio
    shots, and had to subsequently back off on the aperture to retain detail - with my own
    eyes no less, no "unnatural devices" required... I'm not sure when it became "in vogue" to
    deny real visible optical issues that have been seen, understood and properly avoided for
    decades.

    Personally I am not one to champion poor techniques or to proudly claim that other poor
    techniques will mask the effects of diffraction as in...

    "In real life - pictures of resolution charts excluded - you are losing more detail and
    sharpness due to poor technique (both shooting and post-processing) than due to lens
    diffraction "

    Each to his own I guess...
     
  14. Regarding diffraction... I'll agree that you would be hard pressed to see any difference in a print made from a crop sensor camera between a
    photograph at f/8 and one at "f/9-10."

    But our OP was shooting at f/18-22. At those apertures you may not notice much difference in drug store sized prints, but the loss of fine
    detail will be noticeable in larger prints. In any case, unless there is some alternate benefit to shooting at such small apertures (e.g. - a photo
    of a foggy scene in which you want really huge DOF) there is no good reason to shoot at such small apertures on a 1.6x crop body.

    Dan
     
  15. A circular polarising filter may be helpful. A clear sky should look blue if the sun is behind you. If it doesn't, then you are overexposing. However, when the sun is to your right or left you can eliminate the reflections of tiny particles in the atmosphere that wash out the sky colour by using the filter. Better CP filters have a mark on the filter ring, which should be aimed at the sun for maximum effect.
     
  16. I am attaching 2 samples to show the problem. My theory about small apertures seems to be wrong because these samples were shot at around f11. My attempt to fix the problem by playing with white balance and saturation was unsuccessful.

    Thanks for all the replies.
     
  17. Michael Liczbanski >> You seem to be mis-informed in terms of diffraction or at least your comments goes to show that you have not done any serious experimentation with small apertures and prints. Diffraction is a serious limitation. I'm not even gonna bother arguing with you. You should maybe hit a few google searches on the topic and do some real life experiments before you come on there and tell people that diffraction limit is only for pixel peepers. I've had many images ruined back in the days when I didn't know about diffraction limitations. I don't want to see that happen to others.
     
  18. One thing to note regarding crop sensors....

    Diffraction starts to become an issue above f/16 on full frame sensors, while it starts to show up above f9/10 on crop sensors.

    So unless you are doing macro work, the rule of thumb is f/11 max on crop sensors, f/16 max on full frame.

    I've also heard that the 'limit' is partially governed by the megapixel-sensor size ratio... ie.... an 8.2mp 1.6x camera will have a higher tolerence than a 10.2mp 1.6x camera. This is why the 12.2 MP 5D has a much higher tolerance (f/16) than a 10.2mp 40D with a 1.6x crop sensor.

    Someone feel free to correct me if i'm wrong on this, i'm only repeating what i've read elsewhere.
     
  19. The first picture looks rather underexposed and quite hazy, the second looks to have better exposure, but is quite dull... A polarizer would help here no doubt, as well as turning on the histogram on your camera (hit the info button beside the LCD). If it is all bunched up left of center, then the picture will be underexposed, rendering blue skies more of a dark grey. Kind of the same way over-exposing will render blue skies white or greyish-white.

    Anyone else have any advice here?
     
  20. zml

    zml

    I've had many images ruined back in the days when I didn't know about diffraction limitations. I don't want to see that happen to others.

    Well, I strongly suspect that among many ways to ruin one's - including yours - images, diffraction plays but a minor part...
     
  21. Hector, your exposures are off, try bracketing the exposures 2 each side 1/2 stops to get a closer exp.

    While not tryin to take sides my take is. with film small apertures caused problems with colour depth. with 3 layers of emultion plus base layer adaquat light was needed to saturate the colour layers evenly. by using small f stops this pulled the light short of the lower and base levels, lowered colour rendition and contrast.Varying with different types of film & emultions as well as the d&p. Now with digital all the lil optic lenses need an even amount of light. therefore a small aperture will pinpoint the center of the sensor but rob the edges of light causing larger falloffs and degraded image Enhancing the appearance of deffraction. anyway sounds like good BS. I get better results staying under f11 even with my Hassy gear :)
     
  22. Blue skies look gray sounds like a sad country western tune.
     
  23. Michael Liczbanski >> "Well, I strongly suspect that among many ways to ruin one's - including yours - images, diffraction plays but a minor part..."

    No, these photos I'm thinking of were technically perfect except for the diffraction problem from being at f/16-22. Like I said, it's a real problem that I didn't know about back then. If you try to sell it off to shooters as being a lab-only-non-real-life phenomenon and people believe you, then you'll end up with people trying to increase depth of field (or even sharpness from using only the center of the lens elements) and end up with diffraction problems.
     
  24. I think I found the answer to my own question. Page 53 of Rebel XTi/400D user's manual says:

    >>> High temperatures, high ISO speeds, or long exposures may cause irregular colors in the image.

    In my case the temperature is always high when I get these strange colors. Case closed?
     
  25. Please disregard my previous post. The people who said that the problem is with my exposures were correct. +1 stop when the sun is bright does solve the problem. Thanks to all who replied.
     

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