Random Question about eyes you might know the answer for.

Iconindustries

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Yesterday I was underneath a car doing up the torque convertor bolts between the transmission and the engine. Some dirt fell into my eye and as I was trying to flick it out with my shirt sleeve I was thinking how good it would be if there was some kinda filter for our eyes.
Second thought was 'Der icon, that's what safety glasses are for.'
As my thoughts tend to run, it brought up the question of 'our eyes are a lens' which is pretty obvious.
But I wonder what focal length our eyes are and what aperture it uses? What about iso, does that also relate to our eyes?

Our eyes are pretty amazing if you ask me.

Someone here might have more of a clue on this than me. Tell me what ya reckon.

I'm off to see if i can find a pair of Hoya UV linear polarised safety glasses. Metal mount preferably.
 

grebeman

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Brady, get some safety glasses no matter what, doesn't matter if they're cool or not.

I reckon our eyes have variable focal length enabled by muscles round the lens that make it change shape to vary where you focus. As for the aperture again we have auto response depending on light levels. Never given iso much thought, but again I wouldn't be surprised if we've got an auto iso system. We got there long before these camera gizmos.

I'm waiting on an appointment at an eye hospital at the moment, perhaps I'll ask if I remember, but a little squemish when it comes to eyes, so might be distracted when I get there.

Barrie
 

BBW

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Well all I know for sure is that my aperture controls and lenses ain't what they used to be... I think that's called presbyopia.:wink:

Yeah, definitely wear protective eyeglasses Brady. And while you're at it, if you are also barraging your ears - wear protection for them, too! Picture me with an apron tied around my waste, wagging my finger at you. Your eyes and your hearing can way to easily be damaged longterm with the kind of work you do.

OK, now I'll take my Mother apron off.:biggrin:

Interesting thread, by the way.

P.S. I see that Barrie and I both reacted pretty much at the same time. Barrie, I hope everything goes smoothly for you at your appointment.
 

Streetshooter

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My eyes are 35mm at ASA 400...
They usually see at 1/125 f11.
Hope that helps....

Icon, safety glasses are a must for us working with tools chaps...!
 

Hikari

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The eye si an amazing thing. The average focal length of the eye is 17mm. With entrance pupils from about 2mm to 6/7mm depending on age. That makes it f/2.4 to f/8.5. Like a digital camera, the sensitivity of the eye varies with conditions--I am not sure I have an ISO, but we can see in bright daylight at f/8.5 and still see at night at f/2.4 which is more than a 5.76 stop difference the pupil would suggest. When light levels are low, color vision disappears. Angle of view is assumed "normal" in a photographic sense which would be like a Panasonic 20mm (about 50 degrees). However, it is not so easily defined as peripheral vision can be up to 180 degrees and it is easy to focus on an object while ignoring things around it. An equivalent shutter speed is somewhat dodgy to give as we don't make still images and persistence of vision makes it odd, but I have heard numbers such as 1/30 and 1/60 quoted. YMMV.
 

Hikari

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Wear safety googles. It is too late in life to learn to play the piano like Ray Charles.
 

kevinparis

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The eye si an amazing thing. The average focal length of the eye is 17mm. With entrance pupils from about 2mm to 6/7mm depending on age. That makes it f/2.4 to f/8.5. Like a digital camera, the sensitivity of the eye varies with conditions--I am not sure I have an ISO, but we can see in bright daylight at f/8.5 and still see at night at f/2.4 which is more than a 5.76 stop difference the pupil would suggest. When light levels are low, color vision disappears. Angle of view is assumed "normal" in a photographic sense which would be like a Panasonic 20mm (about 50 degrees). However, it is not so easily defined as peripheral vision can be up to 180 degrees and it is easy to focus on an object while ignoring things around it. An equivalent shutter speed is somewhat dodgy to give as we don't make still images and persistence of vision makes it odd, but I have heard numbers such as 1/30 and 1/60 quoted. YMMV.
hmmm if the average focal length of the eye is really 17mm and in the world of 35mm film cameras we were told that a 35mm lens was the same FOV as the human eye... then does that mean we all have native sensors with a crop factor of 2 ?

K
 

GaryAyala

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Brady, I echo Hikari, due to the haz mat nature of the "liquids" that may also drop onto your eyes. I strongly recommend goggles over glasses.

Gary
 

Hikari

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hmmm if the average focal length of the eye is really 17mm and in the world of 35mm film cameras we were told that a 35mm lens was the same FOV as the human eye... then does that mean we all have native sensors with a crop factor of 2 ?

K
Only in terms of the Neanderthals who apparently had bigger eyes.
 

Ray Sachs

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My eyes don't zoom too well but they've got killer aperture controls and autofocus. Lousy shutter speed though - I just can't blink any faster than about 1/10. Now that I'm thinking about it, its slower than that.

-Ray
 

OPSSam

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I have no idea on the focal length but my eyes do seem to have a minimum focusing distance of 6 inches. Not bad, but not quite good enough for macro work.

Upon google searching "focal length of the eye":
Seems to be equivalent to a 22mm lens (crop factor not taken into account).
But there are also some that agree with the 17mm posted earlier.
 

Mellow

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Interesting question. If the eye really has a focal length between 17-22mm, why is 50mm considered 'normal'?

I'm assuming the field of the view of the eye, unlike a lens, is very variable in terms of light gathering. I guess you could say the eye 'vignettes', no? So even though we can actually pick out movements at nearly 180 degrees, it's not like we can read a book at that angle. So maybe the 50mm FOV corresponds to the 'best' part of the eye's vision?
 

Hikari

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think something was lost in translation there.... i could read that as being very insulting but i wont and will just go to sleep perplexed


cheers

K
Nothing insulting, just evolutionary. Crop factor, for me, implies looking back to a former standard. Naturally, the users of m4/3 are the latest on the evolutionary road. Except for Neanderthals, who incidentally had bigger brains, I could not think of a different human "format." (I am also in the middle of proofreading 130 odd pages and have lost the ability to think.)
 

Hikari

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I thought 50mm was the "normal" focal length for a lens?
35mm was the odd format out with a historical blip. Technically, the "normal" focal length equals the diagonal of the format--that should be 43mm for 35mm. But someone went with 50mm.
 

Hikari

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Interesting question. If the eye really has a focal length between 17-22mm, why is 50mm considered 'normal'?

I'm assuming the field of the view of the eye, unlike a lens, is very variable in terms of light gathering. I guess you could say the eye 'vignettes', no? So even though we can actually pick out movements at nearly 180 degrees, it's not like we can read a book at that angle. So maybe the 50mm FOV corresponds to the 'best' part of the eye's vision?
"Normal" is considered to be approximately a 52 degrees angular view. This corresponds approximately to the area in the eye that can use or perceive detail. It also happens to be the same angular view of a format when the focal length equals the diagonal of the format. (And am working with numbers from memory)
 

Mellow

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"Normal" is considered to be approximately a 52 degrees angular view. This corresponds approximately to the area in the eye that can use or perceive detail. It also happens to be the same angular view of a format when the focal length equals the diagonal of the format. (And am working with numbers from memory)
Thanks, that makes sense. What's so interesting is that, as was pointed out earlier, the eye can actually perceive objects outside of the 52 degree window, but with less 'detail'. So maybe you can consider the eye to be a wide-angle lens with a really, really bad vignetting problem and poor edge resolution!
 

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