[Leica] How fast is the human eye?

[lrzeitlin at aol.com (lrzeitlin at aol.com)]

Mark writes:

It would be interesting to find out what the average iso the average


photojournist is out there using right now I have no idea.


Seldom have I ever done a shoot in which I didn't wish I could be shooting


at a faster shutter speed and or stopping down one or two more.

- - - - - 
Another interesting question is "How fast is the human eye?" If you can't 
see a scene, does it really exist? Rather than being an exercise in the 
phenomenological philosophies of Berkeley and Hume, one could well take the 
position that shooting pictures of the invisible is out of the main stream 
of normal photography. Philosophy aside, and despite the fact that the eye 
has been compared to a camera, there is very little in the scientific 
literature that directly compares the sensitivity of the retina to that of 
film or a CCD. So here is my guess. I pulled my trusty decades old GE meter 
from a drawer. With the hood off, the meter basically displays light 
intensity in foot candles. I know that photopic vision, the type mediated by 
the cones in the eye and lets you see fine detail and color, works well down 
to one footcandle. A normal eye has an approximate f stop of 3.5 and has an 
integrating function of 1/12 second. This could roughly be compared to the 
shutter speed. So all I had to do was set the meter dial to one footcandle, 
the shutter speed to 1/12 second, and the f value to 3.5 and read off the 
film speed necessary to get a well exposed picture. It comes out to an ISO 
value of approximately 800. So a camera with an ISO of 100,000 is 7 or 8 f 
stops faster than the human eye. That is enough to take fully exposed photos 
on a cloudy moonlight night, or perhaps even bright starlight. I can't wait 
to shoot pictures of black cats in a coal cellar.
Larry Z