human eye - really a 50mm-lens equivalent?

[chmilar]

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]

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]

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.

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]

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]

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]

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]

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

Here's the full text from the wikipedia article I was quoting from...

The retina has a static contrast ratio of around 100:1 (about 6½ 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]

Here's the full text from the wikipedia article 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]

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

 

[jeffy.dee-lux]

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]

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

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]

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]

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]

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]

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]

Missing the point

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]

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]

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.