What ISO does the human eye have ?

Just wondering what the equivalent sensitivity of the human eye is. I'd
guess it's above ISO 400.

 

The eye is extremely sensitive (a couple of photons) but is rather poor in
integrating the signal (just around 100 millisecond or less). ISO or ASA
definitions are hence not appropriate for comparison.

Have a look at http://medfmt.8k.com/mf/eye.html for a detailed discussion.

Gregor

 

The human eye response is very sensitive, but not very fast. In low light it
is very slow. The focal length of the human eye is about 14 to 18 mm. In
the terms of a 35 mm camera it would be about equivalent to a 15 to 17 mm
lens. This is by coincidence!

The field of vision is approximately 160 to about 170 degrees on the
average. The equivalent F stop is about F 2,5 up to about F 11 on a
comparison terms. Each individual is a bit different.

The retina sensitivity also changes as required. This can change to as much
as about 7 to 10 stops. The total range of stops equivalent can be about 18
to 20 stops. Because the retina sensitivity is changing, this means that the
F stop equivalent is changing.

As for the low light condition ASA speed equivalent, this is hard to say.
The longer we are in a dark area, the higher the sensitivity goes up, to a
certain point. From the figures I have read, I would guess it to be
averaging the equivalent to about 1200 ASA or so. This is a sort of guess,
from my personal perception when comparing from what I have seen camera
equipment do. In very bright light it may go down to about 25 ASA
equivalent.

The speed of the human eye response in bright light can be up to about 5 ms
or about 1/200 of a second. This can also vary from one person to the next.

The surface of the retina is spherical. Thus the eye is a spherical lens.
This helps it be in better compensation for the curvature of its lens. The
brain does all the corrections for things to look as perfect as possible.
Because of this, we don't have the visual distortion problems that camera
lenses have.

Are you planning to build one??? Let me know...

--

Jerry G.
=====

Just wondering what the equivalent sensitivity of the human eye is. I'd
guess it's above ISO 400.

 

Don't confuse refresh with integration. At low light levels,
the human eye integrates up to about 15 seconds (Blackwell,
J. Opt. Society America, v 36, p624-643, 1946). The ISO
changes with light level by increasing rhodopsin in the retina.
This process takes a half hour our so to complete, and that
assumes you haven't been exposed to bright sunlight during the
day. Assuming you wear sunglasses and dark adapt well,
You can see pretty faint stars away from a city. Based on that
a reasonable estimate of the dark adapted eye can be done.
In a test exposure I did with a Canon 10D and 5-inch aperture
lens, the DSLR can record magnitude 14 stars in 12 seconds
at ISO 400. You can see magnitude 14 stars in a few seconds.
(Clark, R.N., Visual Astronomy of the Deep Sky, Cambridge U.
Press and Sky Publishing, 355 pages, Cambridge, 1990.)

So I would estimate the dark adapted eye to be about ISO 800.

Note that at ISO 800 on a 10D, the gain is 2.7 electrons/pixel
(reference:
http://clarkvision.com/imagedetail/digital.signal.to.noise )
which would be similar to the eye being able to see a couple of
photons for a detection.

During the day, the eye is much less sensitive, over 600 times
less (Middleton, Vision Through the Atmosphere, U. Toronto Press,
Toronto, 1958), which would put the ISO equivalent at about 1.

Roger
Photos, digital info at: http://clarkvision.com

 

Here do you get these numbers for focal length? I did a google
search and found many "answers" ranging from 17mm to 50mm
(50 is totally absurd). If you look at this "standard" model
of the eye, it seems that the "standard" focal length is about 20mm
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/eyescal.html
The cornea, a meniscus lens, usually has its principle plane in front
of the lens. This implies a longer focal length than the measured
physical size. The lens inside the eye will move the plane
inside the eye, but not by much.

The f/stop maximum in the astronomical community is spec'd at
f/3.5 for a dark adapted human eye. With a maximum aperture of 7mm,
this implies about a 25mm focal length. Astronomical telescope
minimum magnification is commonly cited as an f/3.5 light cone,
meaning if you look through a faster system, the eye's f/3.5
optics can't gather all the light.

The information on the web is VERY confusing, and I haven't seen
what I would consider a good reference. If anyone knows of one,
please let me know.

Retinal sensitivity has nothing to do with f/stop. Like I posted
elsewhere in this thread, the dark adaptation curve shows about
a factor of 60, or 6 stops for the retina. In bright sun, it probably
goes down more. But 18 to 20 stops is not supported
by any data I've seen. Middleton (1958) put the sensitivity
from dark adapted to sun at a factor of 600, or 9.2 stops

I put it at roughly 800, close to your 1200. Assuming ISO 800 for
dark adapted, then 800/600 (the 600 factor from above) = ISO 1.3.

Another question is what is the minimum aperture of the iris? I've
seen it around a mm, but haven't done any measurements. At 1mm, and
a 20mm focal length, you get f/20. Is that the minimum?

Roger

 

The 18 to 20 stops is a bit of a red-herring. To get this figure he
allows the iris to change size over time. If I look into the dark
cave, my iris enlarges, but as I stare at the well lit cave opening,
it contracts. It's similar to letting the camera change it's aperture
to take a sequence of photos that overall, from the first frame to the
last, would also have an 18 to 20 stop range. This is fairly
meaningless.

Haven't read that stuff, do you have a url?

 

50mm in 35mm film equivalence, which sounds plausible. The field of view
might be huge but what you usually focus on is more restricted (in terms
of field of view).

 

I believe I found the answer to focal length of the eye.
Reference: Light, Color and Vision, Hunt et al., Chapman and Hall, Ltd,
London, 1968, page 49 for "standard European adult":

Object focal length of the eye = 16.7 mm
Image focal length of the eye = 22.3 mm

The object focal length is for rays coming OUT OF THE EYE.
But for an image on the retina, the image focal length is what
one wants. E.g. see:
http://galileo.phys.virginia.edu/classes/531.cas8m.fall04/l11.pdf

So this explains the commonly cited ~17mm focal length,
but the correct value is ~22 mm focal length

This then makes more sense for the f/ratio: with an aperture
of 7 mm, the f/ratio = 22.3/7 = 3.2.

Of course these values vary, with cited values from 22 to 24 mm,
same with the aperture. The maximum aperture also decreases
with age.

Roger

 

"Roger N. Clark (change username to rnclark)" <>
wrote in message SNIP

Thanks for the info.

Bart

 

I was told many years ago that the human eye is the equivalent of
about a 45mm lens on a 35mm camera. That is why a "normal" lens is a
50mm lens... not sure why they made it 50mm and not 45mm, I guess it
makes th math easier to multiply focal lengths. In the old days you
could choose from a 50mm, a 100mm, a 150, 200, etc. length lens

robert Strom

 

That is because an average print at normal viewing (say 10 inch or
about 25 cm) distance has a Field-of-View resembling that of a lens of
about 45mm focal length for 35mm film.

Bart

 

The question isn't meaningful, because the human eye has
locally-compensating sensitivity. This is why it is that when see
'negative' ghost images when you look away from something very bright in
a much darker scene.

 

Ah, but so does film There are a number of edge effects,
especially if you play games during development, like developing with
no agitation. There are a few adjacent pixel effects in CCDs, but not
nearly as much as film.

 

In colour mode, or B&W?

 

Eye can adjust its sensitivity depending on light conditions, by millions of
times. Otherwise you couldn't look straight into Sun at noon and then see faint
stars at night. Also if you compare eye to the camera you'll notice that camera
can collect light over long period of time where eye can not and "longer
exposure" of eye to faint source of light doesn't increase perceived
sensitivity of retina. So if you compare apples to apples, you would need to
keep camera's exposure somewhere shorter than 1/10 of sec. and see at what ISO
the camera picks up as much detail as your eye can. I would think it would be
in thousands ISO for B&W and at least 1600 for color vision. With digital
camera it would be easy to estimate. Are you the game?

 

No kidding! I'd guess thousands of times more! You're comparing
apples and oranges. The human eye is infinitely better than any
camera/film ever made. It focuses faster, has huge latitude,
excellent sensitivity, etc etc.

 

When it is young <g>


--
Scott in Florida

 

Colour - but this is actually an old thread with lots of replies.

 

This assumes that the eye has a DQE of roughly 30%.

Joe
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Where do you get this number? I am pretty sure my data
and references can not be off by a factor of 10.

If you look back this thread, I wrote:

Don't confuse refresh with integration. At low light levels,
the human eye integrates up to about 15 seconds (Blackwell,
J. Opt. Society America, v 36, p624-643, 1946). The ISO
changes with light level by increasing rhodopsin in the retina.
This process takes a half hour our so to complete, and that
assumes you haven't been exposed to bright sunlight during the
day. Assuming you wear sunglasses and dark adapt well,
You can see pretty faint stars away from a city. Based on that
a reasonable estimate of the dark adapted eye can be done.
In a test exposure I did with a Canon 10D and 5-inch aperture
lens, the DSLR can record magnitude 14 stars in 12 seconds
at ISO 400. You can see magnitude 14 stars in a few seconds.
(Clark, R.N., Visual Astronomy of the Deep Sky, Cambridge U.
Press and Sky Publishing, 355 pages, Cambridge, 1990.)

So I would estimate the dark adapted eye to be about ISO 800.

Note that at ISO 800 on a 10D, the gain is 2.7 electrons/pixel
(reference:
http://clarkvision.com/imagedetail/digital.signal.to.noise )
which would be similar to the eye being able to see a couple of
photons for a detection.

During the day, the eye is much less sensitive, over 600 times
less (Middleton, Vision Through the Atmosphere, U. Toronto Press,
Toronto, 1958), which would put the ISO equivalent at about 1.

Roger
Photos, digital info at: http://clarkvision.com