human eye - really a 50mm-lens equivalent?

Discussion in 'Digital Photography' started by Ridge08, Mar 12, 2009.

  1. macrumors member

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    #1
    I see this written all over the place but really have no idea what it means. My field of vision is way wider than a 50mm lens affords (yes, I did go down to 33 on my DX). Of course, most of my FoV is out of focus at any given time. And the magnification of a lens at 70mm is about the same size as I see things through my eyes. (At least with objects at a distance: I haven`t tested close-up ones).

    So what`s with 50mm being called "normal"?
     
  2. macrumors 68020

    Raid

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    #2
    I remember hearing this too once, but I think it has more to do with the human field of focus, rather that the whole range of vision including the peripheral.
     
  3. macrumors G4

    Lord Blackadder

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    #3
    You have binocular vision, which increases your FoV for starters. I can't comment much on the 50mm being normal, since I use a crop-sensor camera which makes my 50mm an 80mm or whatever. However, I think it does approximate my FoV through one eye.
     
  4. macrumors 601

    Phrasikleia

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    #4
    I'm going to hasten a rather uneducated guess: does it have to do with perspective distortion rather than with field of view?

    For example:

    [​IMG]

    Or not?
     
  5. macrumors G4

    Lord Blackadder

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    #5
    I think you may be correct. While being trained in photographing archaeological gigs, I was told that a 50mm lens was preferred because it captured perspective and proportion most correctly compared with wide angle lenses.
     
  6. macrumors 601

    Phrasikleia

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    #6
    The more I think about it, it probably does have to do with field of view. The effect in the image I posted above relates more to distance from the object than anything else.

    [Edit: I just read your post, Lord Blackadder. We must have been typing at the same time. So maybe it is a perspective thing, but distance is still an issue. I just lined up a couple of bottles and looked at them up close and from far away. I could see similar changes going on with my naked eye (that is, similar to what the photo shows).

    At any rate: I didn't realize there was another archaeologist here in the photo forum! I've never done any official excavation photography, but have moved my share of dirt and do photograph archaeological sites regularly. :)
     
  7. macrumors 68030

    FF_productions

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    #7
    This article explains a lot, doesn't prove, but the numbers are fun to look at like, how we have 576 megapixel vision..

    Linky
     
  8. macrumors Penryn

    Abstract

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    #8
    I have read the answer somewhere years and years ago, but I honestly don't remember the explanation. :rolleyes:


    Here's a guess: Perhaps it is about perspective, but also what you can focus on. Not everything you see with your eyes is in focus. Not even close. The retina picks up on a lot of things, but you can only focus on an obect that's aligned with the very centre of your eye. The part of your eye that allows you to stare at your fingerprint, focus on a mountain that's far away, watch TV, read text, or drive a car, is called your macula. Old people suffer from age-related macula degeneration, where your macula deteriorates with age so that you have trouble focusing on things. This can actually be treated, but anyway.....


    Perhaps the size of your field of view that's in focus is approximately what you get from the field of view of a 50 mm lens.



    I actually like the previous answers more (regarding perspective), but I just threw another one in there for those who are interested. ;)
     
  9. macrumors 6502a

    brendanryder

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    #9
    from my experiment my 24-70 F/2.8 on my 40D gives me almost exact same "zoom" as my human eye.
     
  10. thread starter macrumors member

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    #10
    Thanks for your replies, everyone!

    Abstract, I was wondering if 50mm referred to the FoV in focus at any given time. But then I read that your eye`s focal length can change here:
    http://webphysics.davidson.edu/physlet_resources/dav_optics/examples/eye_demo.html

    I`m not in any position to evaluate that information, but I`m guessing that if the eye`s focal length changes, then so does the FoV. Isn`t that right?

    EDIT:
    Really interesting article from the B&H website. Is their newsletter always that good?

    I find the claim that we only see color in the center of our FoV odd: though I`m obviously not in lab conditions, I can see all sorts of colors outside of that area.

    Also did the test to find my blind spot; for me, it occurs about 7-9 inches from the monitor.
     
  11. macrumors 68000

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    #11
    there are two arguments for "standard" lenses: 1) it's standard because it's close to the diagonal length of a 35mm frame, or 2) it shows perspective about equivalent to how we perceive it.

    i don't remember what site i read it on, but it said something like this:
    35mm: your field-of-view with eyes forward
    50mm: what you remember of the 35mm scene a few minutes later
    ~85-100mm: FoV of one eye
     
  12. macrumors regular

    S-Man

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    #12
    When I look through my 5D with a Tamron 28-75 mounted, and I hold it up to one eye while opening the other, like I'm looking normally, it appears to be the same at around 70mm...
    I don't know though...
     
  13. macrumors 6502

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    #13
    I think it is the case on full frame - not with a crop sensor.
     
  14. macrumors 65816

    jaseone

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    #14
    Actually I'm a freak and don't have binocular vision! :D I have this rare eye condition where only one of my eyes sees at one time, it caused me to fail the eye exam where you look into that machine thing at the DMV until the optometrist told me to "cheat" and just close one eye at a time.This was after always passing the regular eye chart exams and being able to clearly read the smallest line at the bottom so failing at the DMV really freaked me out a bit!
     
  15. macrumors G4

    Lord Blackadder

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    #15
    What are the chances of that? In that case, the world for you is seen through a 50mm lens.
     
  16. macrumors G5

    Sun Baked

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    #16
    For some reason I don't think an human eye is a lens equivalent.

    Ripping out someones eye and trying to mount in as a lens on your camera, probably will result in a ruined camera, and the police taking your camera away as evidence.
     
  17. macrumors 6502

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    #17
    Hah! Thanks for the laugh, I needed one. :D

    From my experience, a 50mm lens takes a chunk out of my eyesight but the relative size perception doesn't change at all. It's nothing I would stress over, really. As long as it's a good lens!
     
  18. macrumors 68000

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    #18
    I think in a scientific optical sense it is true that 50mm equals the human eye, but in practice we tend to focus in on things and ignore the wide angle view. This makes something like an 85mm more representative. I read that somewhere.

    Of course, some people have more perspective than others...
     
  19. dmz
    macrumors regular

    dmz

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    #19
    The Wet Lens

    Here's another two-cents' worth. The equivalence is somewhat based on the focal length versus imaging plane, i.e. 50 mm is about equal to the width of a 35mm frame, as someone mentioned already - hence the enlargement/reduction of objects is near unity, or 1x in optical terms. I believe that's the effect that is being described as "normal" vision - with a 50-55mm lens, objects appear neither closer or farther than they do to our naked eyes, and of course the perspective distortion is similar to that of our eyes as well.

    Though our field of view is more like a 28mm lens(on a 35mm camera), when concentrating on an object our mental abilities make it seem like we're using a 75-85 mm lens. Of course, changing the film plane's dimensions completely alters the effect - i.e., a 50mm lens shooting on 16mm film (e.g. 50/16=3x zoom) is a telephoto, the same lens used with a 4x5 camera would yield a super-wide angle view (e.g. 50/250 = .2x). In other words, it totally depends on the focal length/image width ratio.

    It's odd that I can't find anything "authoritative" on this subject, I wonder who started this notion, it certainly needs a proper explanation...

    dmz
     
  20. macrumors 601

    gloss

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    #20
    Don't be so sure. I just picked up a Pentax 50mm/f1.4 lens today. With the crop factor on my k10d, it's 75mm. The view through the viewfinder, though, is very, very close to what I see with the naked eye. A little disconcerting, actually.
     
  21. macrumors regular

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    #21
    Right. It is a crop, not a magnification. The image passing through the lens and onto the sensor will be the same at 50mm regardless of sensor/film/whatever as far as magnification and perspective. The change in FOV will change the apparent size of the image when printed of course based on the sensor it is recorded on; but what you see through the viewfinder should be the same, or similar based on the FOV of the particular viewfinder.

    I don't recall where I read it but it was a while ago. Take a camera and a 50mm lens, look through the view finder, then lower the camera without moving your eye. the image you were looking at will/should look about the same size and have the same perspective, with and without looking through the lens. Everything appears 'normal'. Thus, 'normal' lens.

    Many artsy folks have a distinct distaste for the normal feel of a 50mm and depending on my mood i would agree, as gloss says, "a little disconcerting".
     
  22. macrumors 6502

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    #22
    Thom Hogan regards this as a "Photography Myth"...

    http://www.bythom.com/myths.htm

    "I "see" about a 24mm-equivalent field of view, with my vision concentrated on the equivalent of anything from a 80mm to 300mm lens (and this range has narrowed as I grow older)..."
     
  23. macrumors newbie

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    #23
    Field of View and lenses.... in detail

    Actually, 35mm film is called that because the film is actually 35mm tall (or wide when used vertically as movie film), including the sprocket holes and edges. In still photography, the 35mm film strip is run horizontally, and the recorded image spans the 24mm height in between the sprocket holes, and is 36mm wide. The diagonal measure of this frame is 43mm, or close enough to the standard focal length of 50mm. Thus a 50mm lens is considered "normal" for that film image size, yielding aproximately a 1x optical magnification.

    So you can see how another post here is correct that what constitutes a "normal" lens depends on the film image size, measured diagonally.

    Because we have two eyes with mostly (but not completely) overlapping fields of view, the ability to move our eyes, an uneven distribution of rod and cone cells (that detect color and brightness), and a brain that percieves details differently throughout our visual field, it's really tough to equate any lens to human vision. Our eyes, however, do not change focal length. We can focus on things near ot far, but focal length refers to the ability to "zoom" or change the field of view. We have a fixed field of view, but by concentrating on one detail or another, we can *percieve* differing fields of view.

    Incidentally, each human eye has about a a 160 degree wide by 135 degree high field of view, biased slightly down and towards the outside, yielding an effective combined FoV of 200 wide by 135 high. About 120 degrees of the field overlap the other eye to facilitate binocular depth perception. Overall, 200:135 is almost exactly the same aspect ratio of standard "35mm" still photos at 36mm by 24mm, or a 3:2 ratio.

    Chris Rakoczy
    Rakoczy Photography
    http://www.rakoczyphoto.com



    close to the
     
  24. macrumors regular

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    #24
    My understanding is that 50mm is the FOCAL LENGTH of the human eye. The field of view is much wider than that.

    This is the same as the misconception that a 50mm lens is a 75mm (50x1.5=75) on a DX camera. A 50mm lens is a 50mm lens wheter it's on a DX or FX body what changes is the field of view. The DX camera just takes a smaller chunk of the whole image circle.

    Imagine you're looking out a window at some object, without anything else changing the window gets smaller. The object is still the same size but takes up a larger portion of the window now.
     
  25. gnd
    macrumors 6502a

    gnd

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    #25

    Focal length of the human eye
    is about 22mm. Another reference.
    Field of view of the human eye is: 95° out, 75° down, 60° in, 60° up. About 12–15° temporal and 1.5° below the horizontal is the optic nerve or blind spot which is roughly 7.5° high and 5.5° wide.
     

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