Eye Question.

Innocence · Oct 30, 2006

Hi all,

What is the f/stop and shutter speed combo to get the same light as our eye gets in?

As in is there a "standard" benchmark measurement?

ie. f/1, iso100, 1/100 shutter = eye, or something?

Thank you!

Torus34 · Oct 30, 2006

Kinda . . .

Our eyes don't have the same sensitivity to light as a photographic film. We can't really talk about our eyes being 'ISO 400', or some other ISO value.

However, if we want to consider being outside on a normal, bright sunny day, there's an answer of sorts to your question. Our eyes, in such a situation, have adjusted their irises [stopped down] to give us an ideal 'exposure' of the outdoor world. A camera can reach the same 'setting' if you set the aperture to f16 and then set the shutter speed to 1 divided by the ISO rating of the film you are using. If the film is ISO 125 [Kodak Plus X], you would set the shutter speed to 1/125 second. If the film was ISO 400, the correct exposure would become f16 at 1/400 second.

This is called the 'Sunny 16' rule, by the way. It's a simple way to set a camera on a sunny day when you don't have an exposure meter handy.

Hope this helps.

Innocence · Oct 30, 2006

thank you torus for your response.

I was actually aware of this rule but hoped for a generalisation which could also be applied indoors / low light.

I guess it doesnt work because our eyes change shape and the iris(? eye hole?) opens and closes.

I was wondering (in case you wanted to know) because when i walk into a dark area, and I want to take a photo which comes out exactly the way I perceive it, I was looking for a rule to let me do so.

Thanks again thoguh!

toastydeath · Oct 30, 2006

Our eyes register light in a different way than film, and can register even single photon hits in low light conditions. The "film speed" actually increases in our eyes at night far, far beyond what both digital or film could hope to reproduce in a consumer camera.

The technical part behind this change has to deal with how our eyes actually sense light. Each cell is constantly reprocessing photoreceptive chemicals that begin a chemical reaction when hit by a photon. This is what registers as "seeing light," and is responsible for a variety of phenomena, such as that black circle you see if you stare at the sun or another bright source (All the photopsins have been reacted away in that area). So, in dark conditions, there's less light breaking apart these chemicals, and so there's more of the chemical to do detection (why it takes our eyes so long to adjust to the dark, which requires chemical generation, versus light, where the chemicals are destroyed).

The wikipedia articles around the retna have a great selection of information if you are interested in looking into it further.

Innocence · Oct 30, 2006

thanks for the pointer toastydeath.
I will check it out!

W.Smith · Oct 30, 2006

Compare what your eye can see with what cams can capture:

on a moonless night it takes your eye/brain combo a couple seconds to see the landscape. Including even some details. Your cam, however, set at 400 ISO, probably needs something like 10 to 15 minutes exposure for a vague image of that landscape to materialize.

I.o.w. the human eye/brain combo is in essence far superior to anything cameras can do.

Orrin · Oct 30, 2006

Here is an interesting article on this subject:

http://www.renophotoclub.org/pdf/eye_camera.pdf

Innocence · Oct 31, 2006

an excellent read orrin, i think everyone should read it

THORHAMMER · Oct 31, 2006

this topic is very thought provoking...

our eyes are tied into our brain and therefore we are percieving things, and our brain is filling in the gaps in what we see at the same time.. we can distingguish details/emotions/tension etc... that a camera cannot ever see...

very interesting....