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  1. #11
    Rol_Lei Nut's Avatar
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    Quote Originally Posted by Q.G. View Post
    So you think that you need to have black and white vision to see that a red filter darkens a blue sky?
    If so, do get out tomorrow and have a look.
    Last I looked, it made it look strangely red....
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  2. #12

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    And that makes it impossible for you to recognize that it also was darker?
    I'll perform a PubMed search. Maybe someone found a cure for that condition already.

  3. #13

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    Try a red and a polariser together for a more dramatic effect if you shoot the sky at right angles to the sun. I use the word more dramatic advisedly as in Northern lattitudes such as the U.K.(50-60 degrees) I have never noticed it give an over the top near black look suchg as you get with IR film.The effect is really noticeable as you turn the polariser and find that the clouds really stand out. I don't think I'd bother with the polariser if there aren't any clouds. An orange will simply darken a clear blue sky which is better than ending up with a white sky but only marginally so.

    A solid blue cloudless sky as a light or mid grey does very little for me. Fortunately we are seldom afflicted with such a phenomenon in the U.K. :

    pentaxuser

  4. #14
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    Quote Originally Posted by darinwc View Post
    One thing that I noticed though is that looking through the filters it doesnt seem to have much of an effect. I guess my question is more about 'visualization' than use. Why is it that looking through the filter doesnt seem to have much of an effect?
    To fully estimate the effect of the filter, you need to overlay the sensitivity curve of the film with the transmission curve of the filter. Then all will become clear.

    Although the sensitivity curve of your film does not exactly match that of your eye, you can usually estimate a filter's effect by eye... if you are using a typical pan film. If you are using an ortho film or IR film or whatever then of course all bets are off.

    Here is something related that may amuse you...

    http://hyperphysics.phy-astr.gsu.edu...on/candle.html

    Note also that the eyes (and brain) are remarkably adaptive and will conspire to do their very best to counteract any filters etc. you put in front of your eyes or changes in the colour temp or intensity of the illluminant light. I doubt this happens on a quick enough timescale to matter in this case, but I'd not be surprised to hear that the eye adaptively reduces the contrast we perceive in a scene. E.g. something like the Chubb illusion.
    "Only dead fish follow the stream"

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  5. #15
    Christopher Walrath's Avatar
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    For the effect differing color filters will have on different wavelengths, think of a clock. We have three primary colors; red, green and blue. We'll put red at 12 o'clock, green at 4 o'clock and blue at 8 o'clock. There are three complimentary colors; yellow, cyan and magenta. These colors bridge the gap between the primary colors. Yellow resides between red and green at 2 o'clock. Cyan resides between green and blue at 6 o'clock. Magenta resides between blue and red at 10 o'clock.

    Now a color correction filter will allow light of a similar wavelength to pass through or transmit through the filter while blocking other colors to an increasing degree until you work your way around the wheel to that color's complimentary color (P.C. Red- C.C. Cyan, P.C. Blue- C. C. Yellow, P.C. Green- C.C. Magenta). So if you employ a red filter, it will allow more red light to pass and block out your green light and will have the most impact on blue. If you use a blue filter it will transmit blue light and block out your reds. Yellow filters will raise your yellows and greens and block down your blues, though not to the degree a comparable red filter would.

    That's the basics. Hope it helps.
    Thank you.
    -CW

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  6. #16
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    It's the Angle

    Quote Originally Posted by Q.G. View Post
    A polarizer may work, and it may not. Even when skies are deep blue..
    Depends largely on the angle of sunlight. It needs to be as orthogonal as possible to the sunlight to get the effect. If the sun is behind you, virtually no effect.
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  7. #17

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    And even if at right angle, the effect of a polarizer on the sky may be visible in a small part of the image only, depending on the angle of view of the lens.


    Re the visibility of the effect when looking through the filter: just look through it and you will see whether it has one or not.
    These contrast filters are not 'fine tuning' thingies, but rather coarse affairs.
    Coarse enough not to be able to trick our eyes.

    You can even judge whether any of these have an effect on the sky by looking at the sky without filter. If deep blue, the effect will be strong. If a lighter blue, a moderate effect. If a hazy light blue, the effect will be minimal. If rather white than blue, no effect at all.

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