The human eye, what can it see?

Discussion in 'Beyond the Basics' started by BLD_007, Mar 10, 2010.

  1. BLD_007

    BLD_007 TPF Noob!

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    The human eye, what can it see?

    What is the ISO range of the eye?
    What is the Fstop range of the eye?
    Our eye has one shutter speed, what is it?

    Just wondering...
     
  2. burnws6

    burnws6 TPF Noob!

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    Hot chick=

    f1.4

    ugly naked grandma=

    f22



    That's all I know
     
  3. BLD_007

    BLD_007 TPF Noob!

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    should it not be the other way around? With an F22 the hot chick will all be in focus, and with a f1.4 you only have to see the face and the rest would be blurry.
     
  4. burnws6

    burnws6 TPF Noob!

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    Oh god....clearly...I wasn't talking in literal terms. I was referring to the general reaction of ones eye (widening or squinting)

    Here's your answer






    :)
     
  5. anm90

    anm90 TPF Noob!

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    I thought of it in terms of depth of field! When you see the hot chick, your eye goes to f/1.4 so all you can see is the hot chick, and when you see the ugly naked grandma you go to f/22 so you can see everything around her and not be forced to stare at the only thing in focus... :lmao:
     
  6. Dao

    Dao No longer a newbie, moving up!

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    I think it depends on the environment. Sunny day (outdoor) will be different than candle light (indoor)
     
  7. ann

    ann No longer a newbie, moving up!

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    it is my understanding that the eye, and of course the brain which is involved can only focus on one plane at a time, so it is basically unimportant which fstop.


    If you mean, what can the eye can differentitate then the contrast ratio is "1:10,000. Which is a range of about 14EV". *

    * Christian Block


    And by the way, the example used in several comments is why a lot of women get turned off my junvile men.
     
  8. skieur

    skieur TPF Noob!

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    Well on the dark end of the spectrum, the eye can see at the equivalent of ISO 800, which means that with a digital camera at ISO 1600 or so, you can take a photo of what the eye can't see, because of the lack of light.

    I did some shooting down in a mine under the ocean in the pitch dark and in extremely low light. It was quite a challenge.

    skieur
     
  9. KmH

    KmH Helping photographers learn to fish Supporting Member

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    http://en.wikipedia.org/wiki/Human_eye

    Dynamic range

    The retina has a static contrast ratio of around 100:1 (about 6 1/2 f-stops). As soon as the eye moves (saccades) it re-adjusts its exposure both chemically and geometrically by adjusting the iris which regulates the size of the pupil. Initial dark adaptation takes place in approximately four seconds of profound, uninterrupted darkness; full adaptation through adjustments in retinal chemistry (the Purkinje effect) are mostly complete in thirty minutes. Hence, a dynamic contrast ratio of about 1,000,000:1 (about 20 f-stops) is possible.[3] The process is nonlinear and multifaceted, so an interruption by light merely starts the adaptation process over again. Full adaptation is dependent on good blood flow; thus dark adaptation may be hampered by poor circulation, and vasoconstrictors like alcohol or tobacco.
    The eye includes a lens not dissimilar to lenses found in optical instruments such as cameras and the same principles can be applied. The pupil of the human eye is its aperture; the iris is the diaphragm that serves as the aperture stop. Refraction in the cornea causes the effective aperture (the entrance pupil) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it can range from 2 mm (f/8.3) in a brightly lit place to 8 mm (f/2.1) in the dark. The latter value decreases slowly with age, older people's eyes sometimes dilate to not more than 5-6mm.
     
  10. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    The important part to note is that our eyes are constantly adjusting to what we're looking at.

    Take a sunset landscape scene for example. We look at the bright sky, our eyes adjust to it and it looks nice. We then glace down to the much darker foreground. It may take a fraction of a second or longer, but our eyes adjust to it and we can see some or all of the detail.
    Our brain puts the whole thing together, so what we remember is a whole scene that looks good.

    A still camera, on the other hand, takes exposures one at a time...and each exposure can only have one exposure value. So if you set the exposure for the sky, the foreground will be too dark...if you expose for the foreground, the sky is too bright and gets washed out.

    So when you are taking a photo, it helps to think about the dynamic range of your camera/film and know it's limitations. You might see a beautiful scene, but you should be able to recognize if it will make a beautiful photo...or at least realize that a photo won't look like how you remember it. A common thing to do, is to bracket your exposures and then pick the one you like best.

    Of course, you can use grad filters or selective editing to help a photo look more like how you remember it...and now it's not hard to implement HDR techniques to blend multiple exposures.

    Wow...that was longer than I meant it to be.
     
  11. BLD_007

    BLD_007 TPF Noob!

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    So most sunset pictures are "HDR"? Multiple exposes blended together?
     
  12. Gaerek

    Gaerek TPF Noob!

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    I don't think that's what he said. He said if you want that scene with a high dynamic range to look like you remember it, you can use HDR as one technique. Grad filters and other techniques (exposing for sky, then exposing for foreground, and compositing them in PS, for exampe) are other techniques. I've never used HDR on a sunset or any of the other techniques. I might try it some other time, but I really like the silouetted look.
     

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