Focal length of what eye sees

Discussion in 'Photography Beginners' Forum' started by jamesino, Apr 27, 2008.

  1. jamesino

    jamesino TPF Noob!

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    It is often heard that the perception of the human eye is roughly equivalent to a 50mm focal length. However, suppose I take a full-frame camera and attach a lens onto it. I look through the viewfinder with one eye and keep both eyes open, and zoom in and out (changing the focal length), until both eyes sees the same image, the reading on the lens is closer to the 70-80mm range. Why is this?
     
  2. Alpha

    Alpha Troll Extraordinaire

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    Think of the human eye as a wide-angle lens with a focal length of 17mm
     
  3. JIP

    JIP No longer a newbie, moving up!

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    The focal length comparison to your eye all depends on the film/sensor size. For example for 35mm a 50mm lens is the "normal" focal length while a standard "APS" sized sensor might be more like 30mm or so and 645 medium format is more lie 75mm. As far as what the focal length of what your eye actually sees this is pretty hard to quantify as you can see very wide wih your peripheral vision but most people can also focus on very distann objects as well.
     
  4. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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  5. jamesino

    jamesino TPF Noob!

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    When it is said that the 50mm is equal to what the human eyes see, is that the magnification of the objects of what the human eye sees, or the FOV of what the eye sees?
     
  6. molsen

    molsen TPF Noob!

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    magnification i think. i dont think there is a lens capable of producing the field of view of the eye at the same magnification....

    it's hard to explain..... we see in 3d but an image from a camera is represented in 2d. although both the human eye and camera lenses use the same basic principles to grab light and focus it, the light receptors inside the human eye are in a concave shape, while the sensor of a camera is flat

    it would be almost impossible to recreate the magnification + field of view of the human eye into a 2d form.
     
  7. RyanLilly

    RyanLilly No longer a newbie, moving up!

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    It is kind of a weird concept, I think that the human angle of view is around 170ยบ+ but when you focus on distant object, my brain tends to concentrate on the object and disregard things that are closer to me. I think that the brain just has a much more complex image processor than most cameras.
     
  8. Garbz

    Garbz No longer a newbie, moving up!

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    You are forgetting crop and magnification.

    The human eye sees a 50mm fov with regards to the level of perspective distortion. Clearly it can see the equivalent of 15mm or thereabouts with regard to actual field of view.

    Based on this idea that 50mm is the way the human eye sees many cameras follow that.

    Both my D200 and my 1970s era Nikon FE if I open both eyes I will see @50mm the same through the viewfinder as my free eye. The difference is of course the viewfinder of the D200 is cropped to make the image smaller.

    If you look through at 50mm and it's not the same thing your eye sees then your viewfinder is magnifying the image. This is not uncommon either.
     

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