The Human Eye.

E

elainethepain

Messages
85
Edit My Images
No
Ok i might be posting this in the wrong place but i have a question that needs an answer.

Ok here it is, I was wondering we get lenses that have zooms from 10-20mm,18-50mm, 70-200mm so on and so on BUT (ok i might not put this out right) what would the human eye's focal scale be?


Is it a prime or zoom we have fitted in our heads?. This might be a strange thing to ask but i was wondering about this today and thought i would pop the question on here.(y)
 
They reckon aroung 58mm is the average focal length of the human eye, and this can be kind of confirmed by fitting a 50mm lens on a camera body and looking through the eyepiece with one eye while looking at the same scene with the other eye. They should appear nearly the same.
 
Just reminded me of this :D :

Red Dwarf said:
Lister: Any problems?
Kryten: Well, just one or two. In fact I've compiled a little list if
you'll indulge me. Now then, uh, my optical system doesn't
appear to have a zoom function.
Lister: No, human eyes don't have a zoom.
Kryten: Well then, how do you bring a small object into sharp focus?
Lister: Well, you just move your head closer to the object.
Kryten: I see. Move your head ... closer, hmm, to the object. All
right, okay. Well, what about other optical effects, like split
screen, slow motion, Quantel[tm]?
Lister: No. We don't have them.
Kryten: You don't have them -- just the zoom? Hmm. Well, no, that's
fine, that's great, no, no, that's really great, that's great.
Now then, my nipples don't work.
Click to expand...
 
Chillimonster said:
They reckon aroung 58mm is the average focal length of the human eye, and this can be kind of confirmed by fitting a 50mm lens on a camera body and looking through the eyepiece with one eye while looking at the same scene with the other eye. They should appear nearly the same.
Click to expand...

Ahh, I must try this.

:thinking:
 
Chillimonster said:
They reckon aroung 58mm is the average focal length of the human eye, and this can be kind of confirmed by fitting a 50mm lens on a camera body and looking through the eyepiece with one eye while looking at the same scene with the other eye. They should appear nearly the same.
Click to expand...

Full frame.

crop sensor like canon XXd/XXXd would be ~35?

YMMV however, personally I find 70 on a crop to be about right (but I wear some glasses of around 9 dioptre anyway)
 
coldpenguin said:
Full frame.

crop sensor like canon XXd/XXXd would be ~35?

YMMV however, personally I find 70 on a crop to be about right (but I wear some glasses of around 9 dioptre anyway)
Click to expand...

Nope - works just the same on cropeed or full frame as the ANGLE OF VIEW is the same no matter what size sensor is used. It's just that on a 50d etc you will only be looking at the centre portion of the image.
 
Chillimonster said:
Nope - works just the same on cropeed or full frame as the ANGLE OF VIEW is the same no matter what size sensor is used. It's just that on a 50d etc you will only be looking at the centre portion of the image.
Click to expand...

Bear in mind that on many DSLRs, the viewfinders have some sort of magnification. On the 50D for example, it's 0.95x.

The eye's focal length is a confusing thing. The area you're aware of is different from the area you can see or the area you can do something about. If a rock was coming towards your head from 80 degrees to the direction you were looking you'd still duck. You may even not know why or what was going on. Your brain has 3 different systems to process vision that all deal with different aspects.
 
Of course, for spectacle wearers, things are different again :|.

Field of view varies according to whether they're on full frame ...

elvis.jpg



... or cropped frame :D!


benny.jpg
 
Comparisons between cameras and the human eye are interesting, but ultimately they are not very relevant because what we really see with is the brain. The eye is just a component in the system, but, and assuming you have two of them, the angle of view can be said to be anywhere between 180 degrees and less than 5 degrees depending on what aspect of sight you're talking about, so you could argue a zoom function of some sort, and they are stereoscopic movie scanning devices. A camera just records a single 2D frame, fixed angle.

The eye focuses by changing focal length, but it's roughly 20mm with a maximum aperture around f/2.8. Effective shutter speed is approx 1/20sec, which is why moving pictures projected at 25fps appear continuous. I guess we all vary a bit, glasses notwithstanding, and I seem to remember that women have a fractionally wider field of view and have slightly better colour vision, or rather better colour recall, which is a brain function. Eg, when a woman says it's blue, don't argue chaps :D

Camera viewfinders and focal length are confusing and because of sensor format. With DSLRs, the viewfinder magnification is always quoted with a 50mm lens for historical reasons. The fact that this ends up with an approximately life-size view is coincidental.

When people say that a 50mm lens on a full frame camera has the same angle of view as the human eye, it is of course not literally true. Ditto for a 30mm lens on crop format. However, I think there is something in this because an angle of view very roughly around 40 degrees equates quite well to the field of 'high awareness' that we see. That's about the kind of area that we scan with our eyes, without moving our heads. And if you take a picture with a lens like that, generally speaking the perspective looks natural and the distance about normal.

But since the whole thing is processed through the brain, which can (and often does) change everything, then the camera/eye comparison doesn't seem to help with much photographically speaking.
 
Chillimonster said:
They reckon aroung 58mm is the average focal length of the human eye, and this can be kind of confirmed by fitting a 50mm lens on a camera body and looking through the eyepiece with one eye while looking at the same scene with the other eye. They should appear nearly the same.
Click to expand...

That would make it 58mm equivalent (i.e. the same fields of view) not the same focal distance - from pupil to the retina it is nowhere near 58mm ;)

I guess this is one of the reasons why 50mm range is called normal - it is the same as the normal human field of view.
 
pearce_jj said:
Great post Hoppy, thanks (y)
Click to expand...

Thank you JJP :)

I thought of another thing, just by way of interest.

The focal length of the eye refers, I think, to the whole 'system' - that is the lens and retina, but also the cornea which does most of the bending of light to a sharp image. The lens is a fine focusing mechanism (internal focusing in effect) which it does by changing shape and focal length as it is pulled by muscles.

As we get older, the lens gets stiffer and can't be pulled so easily to cover focusing range, the 'accommodation' is reduced, so we need glasses/contacts to help with either close or far vision, or both in my case.
 
My goodness we are getting technical now eh, Here was me thinking i was asking a simple/daft question.lol.
 
I think that 35mm cameras traditionally came with 50mm lenses because that closely equated to the field of view of the human eye.
 
arclight said:
I think that 35mm cameras traditionally came with 50mm lenses because that closely equated to the field of view of the human eye.
Click to expand...

The human eye has a field of view anything between 180 and less than 5 degress, so it needs to be qualified. As above.
 
Quote:
Originally Posted by arclight View Post
I think that 35mm cameras traditionally came with 50mm lenses because that closely equated to the field of view of the human eye.
The human eye has a field of view anything between 180 and less than 5 degress, so it needs to be qualified. As above.


Yes, silly me, you are correct, I used the wrong term.
 
You must log in or register to reply here.
Back
Top