F stop of the human eye?

J

Jonathan12uiz

Well-known member
I'm a noob and I was wondering what f stop would be the equivalent to the human eye.

Like when I look down a dimly lit hallway. How do I know what aperature I should set it to be exactly what I'm visually registering with my eyes.

Or is it just how I think it goes... Where since your pupils contract and dialate like the aperture on a camera it's always a guessing game and u just shoot and compare to the picture?

I was wondering this because how did they know what f stop to set a film camera to in any given situation without wasting film with bad pics.
 
Is that basically the equivalent to the exposure meter on most dslrs nowadays. The meter that shows how under or overexposed the pic will be?
 
A light meter will tell you if you've exposed correctly, you have one built into your DSLR. The human eye does not have an ASA rating so you can't compare the two.
 
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Reason I'm asking is because I can snap the pic where the meter is in perfect exposure, but when I look at the pic on the monitor it doesn't really look exactaly like how my eyes are seeing.

I'm wondering because to match what ur eyes are seeing how do u know to how much to under or overexposed to match.
 
I can put a f1.4 on my 5D shoot at 6400 ISO at 1/30 shutter speed in a parking lot at midnight and be over exposed. I can stop down to f10 at 100 ISO at 1/5000 in broad daylight and be underexposed.

Your eye has an iris that "stops" down the light input of your eye or opens it up to let more light in. But your eye doesn't have shutter speeds or ISO like your camera to change exposure.
 
Using light meters is a technique to itself. The ones built in to cameras can't get specific readings of certain sections of the scene, so it's easy for mistakes to be made. With film you have more latitude to push and pull to the proper exposure if it's off a little bit.
 
Jonathan12uiz said:
Reason I'm asking is because I can snap the pic where the meter is in perfect exposure, but when I look at the pic on the monitor it doesn't really look exactaly like how my eyes are seeing.

I'm wondering because to match what ur eyes are seeing how do u know to how much to under or overexposed to match.
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Which part of the shot are you metering though? An average over the whole image will mean some is under, some is over. Spot metering will expose perfectly for that point and everything else will be out.

http://en.wikipedia.org/wiki/F-number#Human_eye
 
that is wrong, eyes must have an ISO.
There is a minimum level of light where your eyes see nothing and a maximum where your eyes just saturate. (so, the existence of flashlight and sunglasses).
commonly we use the ISO arithmetic scale, corresponding to the ASA system, a doubling of the sensitivity of a film requires a doubling of the numerical film speed value.
basically, the film is exposed at different light level and the curve obtained contains 5 parts (like in video we got knee for example): the base + fog, the toe, the linear region, the shoulder, and the overexposed region.
the speed of the film is taken in a region where the linearity is good and where you can get a defined difference between a low and high point.
This way you can ensure that any film will more or less react the same (as long you stay in that linear zone)

for the eye, it is the same, except this would be very difficult to measure since you have to stop the iris working, and make the measurement would be tricky (measuring voltage on the optical nerve would probably have no meaning)
That said, you will consider that young people would probably get better "ASA" than old ones, especially in color.
An other easier method would be to take picture at eyes condition (speed of shutter, how fast an eye can see ? let say around 1/30 of sec.) of a scene containing cards with numbers in graduated shadow. Then comparing what is visible on the picture and what a sample of people can see.
to make sure you got the right speed, you could move one of the card a constant speed until it become fuzzy enough for people and on the film to say they are on the same setup.
you could even have people to look through a shutter to make sure they do not B-pause .

We know already that the eye field of view is comparable to a 50mm lens.
I would not be surprised to find the the eye is somewhere around 6400 ASA
 
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The eye is variable.
In light it is one range, and in dark it is another, and each person is different.

Hard to determine an exact figure.
You may be able to figure something close to YOUR eye.

To do that, you would have to go in a room that is as dark as you can barely see something.
Take a light meter with you, and see what it reads.
Stop down about 2 stops and take a pic..it should be close.

Do the same thing in bright light, the problem is, you might have a hard time finding a light too bright that your eyes can't adjust to, and then it may be harmful to your eyes.

If you just want to know to know, well there you go...

What I would think would be more useful in the real world is to know how much light you need to shoot a video that would be usable.

With that in mind, I would not use a shutter slower than 30/th sec.
That can apply to stills and video hand held (at least for me).
Your lowest iso is 100, so there are two constants that are constant (at least for me).

So the thing that really matters is how much light do you need to shoot at your lowest f stop.
That can be figured by an incident meter, or a cine meter with the constants as given.
 
The eye has to have some sort of equivalent to a shutter speed right? Otherwise what's all this motion blur I'm seeing when i'm waving my hand in front of my face?
 
I think it's more important to strive for what's good for each particular image in order to put the viewers in the emotional and psychological state you want them at that particular time, rather than copying what your eyes are seeing or what their eyes might be seeing.
 
It depends on how you measure the focal length of the human eye. Since F/stop is a calculation of focal length and opening diameter it is possible to measure. The human eye has an aperture range of f/8.3-2.1 (or 3.2 depending on how you measure focal length.) However there is no clear way to measure the ASA or "shutter-speed" (your eye can see things differently if it looks at them longer...think distant stars.) Anyway, it is easy to calculate the f/stop of an eye, but not so much to tell what that means.
 
Jonathan12uiz: Please tell us why you want to match the f-stop on your lens with your eyes. I just don't see what the point is.
 
I've heard if you rub freshly grated carrots on the sensor of Eos cameras it can improve the low light performance by up to 2 stops. But be aware, it may void your warranty.
 
evilken said:
I've heard if you rub freshly grated carrots on the sensor of Eos cameras it can improve the low light performance by up to 2 stops. But be aware, it may void your warranty.
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Why go to the trouble when you can simply save "C40H56" in a text file on the camera's memory card?
 
The way the eye handles light is hard to determine as we "see" only the results that come after that big Digic-Chip between your ears. Yes, I mean the brain. The brain uses hundreds of tricks to get the pictures in our head right, e.g.:

Image stabilization: did you every find walking around annoying because of the shaky vision? Probably not, because the brain is pretty good at stabilizing the image.
White balance: Did you ever have to wear tinted glasses to match the white balance between indoors and outdoors? Probably not, because the brain adjusts the way we perceive colour.
This could go on. Just read about optical illusions.
So determining the F-stop, Iso or shutter-speed of the eye is difficult because we can't be sure what the brain does after the neurons of the eye fired the information down the optic nerve.
 
Also don't forget that your eyes only actually see a very small area at any one time. You always have to move your eyes and dart them for your brain to form any image. Editing plays more to what you see than f/stop.

Therefore, I suggest you get a lensbaby set to wide open aperture, have the shutter between 1/50 - 1/100, have auto ISO, and do a composite of images :p
 
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