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View Full Version : human eye - really a 50mm-lens equivalent?




Ridge08
Mar 12, 2009, 09:02 PM
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"?



Raid
Mar 12, 2009, 09:06 PM
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.

Lord Blackadder
Mar 12, 2009, 09:11 PM
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.

Phrasikleia
Mar 12, 2009, 09:12 PM
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:

http://upload.wikimedia.org/wikipedia/commons/e/e5/Focal_length.jpg

Or not?

Lord Blackadder
Mar 12, 2009, 09:15 PM
I'm going to hasten a rather uneducated guess: does it have to do with perspective distortion rather than with field of view?

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.

Phrasikleia
Mar 12, 2009, 09:16 PM
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. :)

FF_productions
Mar 12, 2009, 11:36 PM
This article explains a lot, doesn't prove, but the numbers are fun to look at like, how we have 576 megapixel vision..

Linky (http://www.bhphotovideo.com/c/find/newsLetter/The-Photographic-Eye.jsp)

Abstract
Mar 13, 2009, 12:04 AM
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. ;)

brendanryder
Mar 13, 2009, 12:22 AM
from my experiment my 24-70 F/2.8 on my 40D gives me almost exact same "zoom" as my human eye.

Ridge08
Mar 13, 2009, 12:28 AM
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.

toxic
Mar 13, 2009, 01:13 AM
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

S-Man
Mar 13, 2009, 01:45 AM
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...

bertpalmer
Mar 13, 2009, 04:03 AM
I think it is the case on full frame - not with a crop sensor.

jaseone
Mar 13, 2009, 01:17 PM
You have binocular vision, which increases your FoV for starters.

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!

Lord Blackadder
Mar 13, 2009, 06:58 PM
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...

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

Sun Baked
Mar 13, 2009, 07:05 PM
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.

LittleCanonKid
Mar 13, 2009, 07:33 PM
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.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!

carlgo
Mar 14, 2009, 09:08 AM
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...

dmz
Mar 14, 2009, 01:57 PM
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

gloss
Mar 17, 2009, 04:45 PM
I think it is the case on full frame - not with a crop sensor.

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.

H2Ockey
Mar 17, 2009, 05:15 PM
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.

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".

sonor
Mar 17, 2009, 05:16 PM
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)..."

rakoczyphoto
Jan 24, 2011, 04:01 PM
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 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.

AML225
Jan 31, 2011, 08:57 AM
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.

gnd
Jan 31, 2011, 11:04 AM
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.


Focal length of the human eye (http://hypertextbook.com/facts/2002/JuliaKhutoretskaya.shtml) is about 22mm. Another reference. (http://www.shutterphoto.net/article/the-focal-length-of-the-human-eye/)
Field of view of the human eye (http://en.wikipedia.org/wiki/Human_eye#Field_of_view) is: 95 out, 75 down, 60 in, 60 up. About 1215 temporal and 1.5 below the horizontal is the optic nerve or blind spot which is roughly 7.5 high and 5.5 wide.

chmilar
Jan 31, 2011, 01:47 PM
Just to muddy the waters a little more:

If you are looking at a printed photograph, what constitutes normal perspective and field of view depends on the print size and viewing distance.

For example, if you shoot a scene with an ultra-wide lens, print it really huge (40x60 inches), and view it from a couple of feet away, it will match how you saw the scene when you were there. It will also show a very wide field of view.

So a "normal" lens matches your eye's perspective when viewing a "normal" sized print from a "normal" distance.

The example of looking through a camera's viewfinder, and holding the other eye open, is false. It depends on the viewfinder magnification.

rakoczyphoto
Feb 7, 2011, 06:57 AM
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.

You're correct that the lens doesn't change however the APS-C sensor and other "crop factor" cameras don't make a lens change, they produce an image EQUIVALENT to using a longer focal length lens on a "full frame" SLR. In other words a 50mm lens acts like a 75mm on a camera with a 1.5 crop factor. Or it takes a 75mm lens on a full frame SLR to produce an image similar to what a 50mm on a 1.5x cropped camera produces.

Your analogy of looking at an object through a window is a good one.

-RakoczyPhoto

VirtualRain
Feb 7, 2011, 11:28 AM
Focal length of the human eye (http://hypertextbook.com/facts/2002/JuliaKhutoretskaya.shtml) is about 22mm. Another reference. (http://www.shutterphoto.net/article/the-focal-length-of-the-human-eye/)
Field of view of the human eye (http://en.wikipedia.org/wiki/Human_eye#Field_of_view) 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.

;) About 180 deg. field of view with both eyes.

Another interesting fact: he 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.

Also... We have a dynamic range of about 1,000,000:1 or 20 stops!

carlgo
Feb 8, 2011, 11:09 PM
Whatever focal length our eyes may be, we don't have much of a depth of field and only see a thin slice of things in good focus at any one time. We simply keep refocusing on things.

Some, like successful baseball players, have very fast focus times.

Funny that when we take a photo, we usually try to get as much in focus as possible which is the complete opposite of how we see the real world.

Chip NoVaMac
Feb 9, 2011, 12:20 AM
I personally think that each of us develops a "FOV" that suits us. In my early days of 35mm photography that was that of the 50mm FOV. Later on I began to see things that fit the 24mm FOV in 35mm terms.

The 50mm FOV comes from rangefinder days.... in that the right eye was in the finder and the left eye was free to "view the world" - a good view finder allowed for that view.

jared_kipe
Feb 9, 2011, 12:38 AM
Also... We have a dynamic range of about 1,000,000:1 or 20 stops!

Maybe during the day, when our eye's sensitivity is about ISO 1!

VirtualRain
Feb 9, 2011, 02:31 AM
Maybe during the day, when our eye's sensitivity is about ISO 1!

Here's the full text from the wikipedia article (http://en.wikipedia.org/wiki/Human_eye#Dynamic_range) I was quoting from...

The retina has a static contrast ratio of around 100:1 (about 6 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.

jared_kipe
Feb 9, 2011, 01:30 PM
Here's the full text from the wikipedia article (http://en.wikipedia.org/wiki/Human_eye#Dynamic_range) I was quoting from...

I was just musing about the fact that our eyes are much less sensitive than any modern digital camera. During the day ISO 1, fully dark adjusted roughly ISO 800.

800->400->200->100->50->25->12.5->6.3->3.2->1.6->0.8 (~1)
10 stops of sensitivity range

6.5 stops of bit depth (as cited by article (static contrast))

Eye's min aperture f/8.3, max f/2.1
8.3->5.9->4.2->3.0->2.1
4 stops of aperture range.

10+4+6.5=20.5
So hence the wikipedia quoted dynamic contrast ratio of 20 stops.

VirtualRain
Feb 9, 2011, 01:35 PM
I was just musing about the fact that our eyes are much less sensitive than any modern digital camera. During the day ISO 1, fully dark adjusted roughly ISO 800.

800->400->200->100->50->25->12.5->6.3->3.2->1.6->0.8 (~1)
10 stops of sensitivity range

6.5 stops of bit depth (as cited by article (static contrast))

Eye's min aperture f/8.3, max f/2.1
8.3->5.9->4.2->3.0->2.1
4 stops of aperture range.

10+4+6.5=20.5
So hence the wikipedia quoted dynamic contrast ratio of 20 stops.

Right. Nice. So how much dynamic range do modern cameras have? 10-11 stops? Sensor tech has a way to go. However, I guess we should be thankful we don't need to wait 30 minutes for our cameras to adjust to high ISO for shooting in the dark :p

jeffy.dee-lux
Feb 9, 2011, 02:05 PM
one thing to keep in mind - the size of the view finder in a camera.

I used to think this lens equivalent thing meant that if you look through a camera with a 50mm lens, the magnification would be about the same as looking without the camera. But that totally depends on how big the view finder image is, or the LCD screen you might be looking at instead.

I think it really has to do with perspective. I think a good test would be to compare parallel lines that converge in the distance. A telephoto lens will flatten them out while a fisheye would make them appear far more angled.

I don't know if angle of view necessarily would have to come into this. A 50mm lens with an overly obstructing lens hood around it would still be a 50mm lens right? Either way, very interesting discussion.

jared_kipe
Feb 9, 2011, 02:12 PM
Right. Nice. So how much dynamic range do modern cameras have? 10-11 stops? Sensor tech has a way to go. However, I guess we should be thankful we don't need to wait 30 minutes for our cameras to adjust to high ISO for shooting in the dark :p

My 5DmkII + Sigma 50mm f/1.4 + RAW
from http://www.dpreview.com/reviews/CanonEOS5DMarkII/page25.asp we see that from ISO 50 to 6400 we have at least 7.7 stops of usable range, higher ISO compromises the usable dynamic range by a stop.

6400->3200->1600->800->400->200->100->50
7 stops of ISO
7.7 stops of usable bitdepth (as quoted from article)
f/16->11->8->5.6->4->2.8->2->1.4
7 stops of aperture range

Put it all together 7+7+7.7 = 21.7

2^21.7 = 3,406,833:1 dynamic range

So 1.7 stops more than the cited range of the eye. 2^1.7=~3.25x the dynamic range of the eye.

jeffy.dee-lux
Feb 9, 2011, 04:28 PM
My 5DmkII + Sigma 50mm f/1.4 + RAW
from http://www.dpreview.com/reviews/CanonEOS5DMarkII/page25.asp we see that from ISO 50 to 6400 we have at least 7.7 stops of usable range, higher ISO compromises the usable dynamic range by a stop.

6400->3200->1600->800->400->200->100->50
7 stops of ISO
7.7 stops of usable bitdepth (as quoted from article)
f/16->11->8->5.6->4->2.8->2->1.4
7 stops of aperture range

Put it all together 7+7+7.7 = 21.7

2^21.7 = 3,406,833:1 dynamic range

So 1.7 stops more than the cited range of the eye. 2^1.7=~3.25x the dynamic range of the eye.

well there are two different questions here: how much instantaneous dynamic range, as in what can you take in all at once in one "image", vs how much overall dynamic range allowing for changes in camera settings, pupil dilations and eyeball chemistry.

jared_kipe
Feb 10, 2011, 10:58 AM
well there are two different questions here: how much instantaneous dynamic range, as in what can you take in all at once in one "image", vs how much overall dynamic range allowing for changes in camera settings, pupil dilations and eyeball chemistry.

The usable range has already been stated for both the camera and the eye.

6.5 stops for the eye
7.7 stops for the 5DmkII

VirtualRain
Feb 10, 2011, 12:05 PM
The usable range has already been stated for both the camera and the eye.

6.5 stops for the eye
7.7 stops for the 5DmkII

There's got to be something off here... basic observation says my eyes have more dynamic range than my camera.

jared_kipe
Feb 10, 2011, 01:24 PM
There's got to be something off here... basic observation says my eyes have more dynamic range than my camera.

I can think off the top of my head two reasons why you feel this way.

#1, Human eyes have a very powerful software engine behind them and are constantly shifting, integrating, and changing exposure. Our brains also don't care very much about anything that isn't in the center of your view (if it does you will shift your eyes towards it and refocus/expose). It is almost impossible to look out say your window and stare straight ahead and appreciate the scene.

#2, Camera RAW captures significantly more data (range) than can be represented in an 8-bit image. RAW converters, and cameras themselves apply contrast to the file to present something that looks appealing to us. A quick search turned up this http://www.cambridgeincolour.com/tutorials/RAW-file-format.htm

About half way down the page is a demonstration of exposure correction applied to a single RAW capture. If you hover over the -1 and look at the sun you can think of the top of the cameras range as where you can still see some color before it goes white. If you hover over the +1 and look at the deepest shadows in the bushes, you can think of this detail as the lowest of the camera's captured range.

So the camera's actual captured range goes from the sun to the dark bushes. This is almost certainly more range than your eye would perceive looking at the same scene. That said, you cannot represent all this range on a normal computer monitor without some tricks, i.e, HDR tone mapping. Here the real limiting factor is the end file format (8-bit JPEG) and the display hardware (Monitors with limited bit depth and contrast), not the camera's ability to record the scene.


Then again, this is just logical reason, not "basic observation".

davillio
Apr 25, 2011, 04:43 PM
Think you might be missing the point slightly. All just a tad to techy.
A 50 mm lens on a 35mm film tends to exclude outside influences.
That is to say it focuses on the reactions and shows life and life only.
An 80mm lens will distort to make life look more beautiful than it really is. It excludes the outside influences.
A 35mm lens will show the pressures and their influence on the central characters.
Watch the films of Ozu. All shot with only a 50mm lens.

acearchie
Apr 26, 2011, 03:04 PM
The usable range has already been stated for both the camera and the eye.

6.5 stops for the eye
7.7 stops for the 5DmkII

I'm not dusputing your figures but merely looking for further explanation. DxOMark says that the 5dii has a dynamic range of 11.9 EVs (http://www.dxomark.com/index.php/Camera-Sensor/All-tested-sensors/Canon/EOS-5D-Mark-II) which I believe is equivalent to f-stops so the details don't match up!

cppguy
Apr 26, 2011, 09:50 PM
The way our eyes see can be very different than how the mind sees.

First of all, we have a surprisingly wide peripheral vision, which gradually fades away. It is very difficult to put a specific number to it. Our vision get blurred on the sides. There's a point where we can no longer recognize shapes, but we still detect motion. This is extremely important in certain sports, such as hokey or basketball, and it can play a role in our survival.

The other important point is that we zoom by cropping. That's why so many times when you go home and download your pictures you remember the scene quite differently. It's easy to get carried away and believe that you have the right composition, when it's only in your imagination. The mind does an incredibly good job throwing away irrelevant information from our view, thinking it doesn't even exist. Only when you take the picture do you realize that trash can in the corner, or that road sign on the side.

Also the brain doesn't store all the information. For example, if you notice someone attractive far away, you're not going to remember the color of the car that just passed. But if it's about to hit you, you'll damn sure jump away. It's very difficult to put a single focal length value to such intelligent image processing.

Finally, when a photo is viewed, you can focus your eyes on an out of focus area. This is the only way we can carefully study what it really looks like up close.