# The human eye, what can it see?



## BLD_007 (Mar 10, 2010)

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...


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## burnws6 (Mar 10, 2010)

BLD_007 said:


> The human eye, what can it see?
> 
> What is the ISO range of the eye?
> What is the Fstop range of the eye?
> ...





Hot chick=

f1.4

ugly naked grandma=

f22



That's all I know


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## BLD_007 (Mar 10, 2010)

burnws6 said:


> BLD_007 said:
> 
> 
> > The human eye, what can it see?
> ...



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.


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## burnws6 (Mar 10, 2010)

BLD_007 said:


> burnws6 said:
> 
> 
> > BLD_007 said:
> ...




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


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## anm90 (Mar 10, 2010)

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:


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## Dao (Mar 10, 2010)

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


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## ann (Mar 10, 2010)

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.


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## skieur (Mar 10, 2010)

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


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## KmH (Mar 10, 2010)

*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.


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## Big Mike (Mar 10, 2010)

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.


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## BLD_007 (Mar 10, 2010)

Big Mike said:


> 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.
> ...



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


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## Gaerek (Mar 10, 2010)

BLD_007 said:


> Big Mike said:
> 
> 
> > The important part to note is that our eyes are constantly adjusting to what we're looking at.
> ...


 
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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## ann (Mar 10, 2010)

not necessarily.

a setting sun moves very quickly and that movement is not something HDR software is fond of dealing with.

bracketing for the best exposure, is not necessarily the same as one would do for making a wide variety of exposures for an HDR image.


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## kundalini (Mar 10, 2010)

I wish I could upgrade my eyes as easy as lenses.  :sad:



> ....<snip>And by the way, the example used in several comments is why a lot of women get turned off *my* *junvile men*.


   you go girl......





   sorry, couldn't resist


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## Early (Mar 10, 2010)

ann said:


> it is my understanding that the eye, and of course the brain which is involved can only focus on one plane at a time


It is my understanding, too, which brings up another question.  How fast can the human eye focus?

As far as ISO goes, unlike film or dig., our eyes can distinguish detail in some pretty dark shadows.  I'll let our resident scientists take it from there.


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## Big Mike (Mar 10, 2010)

> So most sunset pictures are "HDR"? Multiple exposes blended together?


No, not at all.

But if you look at a lot of sunset shots with those deep, rich colors, anything in the foreground (like a palm tree) is likely a dark silhouette.  We don't often remember seeing only the dark silhouette of the tree, because our eye adjusts to it, but that's what the photo records.


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## Big Mike (Mar 10, 2010)

> As far as ISO goes, unlike film or dig., our eyes can distinguish detail in some pretty dark shadows.


Film or digital can distinguish detail in dark shadows just fine...maybe better than our eye.  It just takes a longer exposure time.  For example, a photo taken for 30 seconds (and decent aperture size) will likely pick up anything with any little bit of light on it.  

The difference is that our eye will look to the shadow, adjust to it, see what's there, then look away and adjust again.


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## Dwig (Mar 10, 2010)

Big Mike said:


> [...
> The difference is that our eye will look to the shadow, adjust to it, see what's there, then look away and adjust again.



Quite true, and it does this for both "exposure" and focus while, at the same time, not usually fixating on any one point, scanning the field instead. You brain then computer processes the incoming data in real time forming a composite image. You are rarely aware of anything being "out of focus".

When it comes to color and exposure, the human eye is a four sensor system rather than the 3 common to color film and most digital cameras (all current commercially available color digitals). The fourth sensor set is a luminance only set that is primarily sensitive in the middle of the spectrum around green. This sensor system is more sensitive to light than the other three and in very low light is used almost exclusively, yielding nearly monochrome images. In bright light it doesn't work well, but the other three cover that end of the intensity range and are each sensitive to different sections of the spectrum yielding color images in much the same way as modern color film and digital sensors.


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## Hamtastic (Mar 11, 2010)

Excellent, short vid on human color perception

Beau Lotto: Optical illusions show how we see | Video on TED.com


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## djacobox372 (Mar 14, 2010)

Eyesight has actually two sensor types: rods and cones. 

Cones are more plentiful (higher resolution) and centered in the middle of the eye, they are sensitive to color and less sensitive to light.  They are your "day vision."

Rods are less numerous and located away from the center of the eye, they are not sensitive to color (especially red).  They are very sensitive to light and prone to be blown out by bright light.  This is why your peripheral vision is actually better in the dark then it is in the daytime, it's also why it's easier to see things slightly to the side at night then it is dead center (where your rods are less numerous).

Interesting fact: rods can actually accumulate light for up to 15 minutes, meaning a very dim light source may not be visible unless you stare at it for 15 minutes... that's a slow shutter speed!


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## Josh66 (Mar 14, 2010)

Here's some interesting reading about the human eye, and how it relates to photography:

Clarkvision Photography - Resolution of the Human Eye


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