Does anyone know the equivalent ASA and f-stop range of the human eye?
Does the eye have some sort of frame rate, sampling rate or refresh rate?
D. A. Oldis writes:
>Does anyone know the equivalent ASA and f-stop range of the human >eye?
>Does the eye have some sort of frame rate, sampling rate or refresh >rate?
Also, is it possible to adjust the eye's refresh rate by going into the control panel?
> Does anyone know the equivalent
ASA and f-stop range of the human >eye?
> Does the eye have some sort of frame rate, sampling rate or refresh >rate?
The human eye can readily adapt to light levels from at least .03 F/C (full moon, no other illumination) for scotopic vision (rods), to 15,000 F/C (bright daylight in snow) for photopic vision (cones).
I'm not sure how that would translate into ASA and f-stop.
Detectable refresh rate (temporal frequency) varies between 40 and 80 hz (depending on the lighting ratio of source to ambient light). The eye can detect flickering (temporal separation) of equal intensity light sources at intervals as low as 15-20 ms.
Finally, resolution is between 50 and 60 cyc/deg. in bright light, but that number has a lot of qualifiers that I won't go into. (Our hearing is limited to 20-20K hz, but the brain can detect missing harmonics at much higher frequencies.)
Los Angeles based Director of Photography
West Coast Systems Administrator, Cinematography Mailing List
>I'm not sure how that would translate into ASA and f-stop.
Jessica quotes a sensitivity range of 500,000:1, or 19 stops. That comes from two factors -
1/. Aperture. The iris opens and shuts, but only over a limited range - approximately 4 stops, or a ratio of 16:1. (That's approximate - of course the eye focuses by changing its focal length, which in turn affects the aperture).
2/. Adaptation, effected by the sensitivity of the rods and cones. This is the closest equivalent to the ASA range of the eye - in film terms. I learnt that this was up to 100,000 to 1, but even 30,000 to 1, or 15 stops (to fit Jessica's figures) is quite impressive.
On top of this of course is the sensitivity range of the retina at any given aperture and adaptation. It's quite a lot more than film, with a _linear_range of 9 stops or so. However, there is a massively extended toe and shoulder, and at extremely bright or dark brightness levels, the eye still has some slightly reduced discrimination. It is estimated that the total potential response range of the eye in all conditions is at least 10^10 to
1. (That’s 10 billion to 1). Maybe 10^12:1.
Why do you ask, D.A. Oldis? Planning to build one?
Group Technology & Services Manager
The Atlab Group
What is relationship between human eye and 24fps ?
Human eye vision is around 60 fps as per our tests of Showscan proved
D.A. Oldis wrote :>Does anyone know the equivalent ASA and f-stop range of the human >eye?
>cheap little DV camera…could
have greater sensitivity than my eyes.
Now are we talking sensitivity, or adaptability? Different things.
>The only thing that gave it away as being night
That's the clue. The eye can, as we've said, adapt over an enormous range. So, to a lesser but still useful extent, can film or video photography. But it's what the brain does with the image that is significant. We can see quite clearly by day or at dusk, and without any external clues, we wouldn't be aware of what the absolute light levels are. But the brain is very smart at picking up the clues: as you say, street lights coming on but also the relative brightness of sun and sky to land, the presence and length of shadows, the colour temperature of the light, all tell the brain how to interpret what it sees.
The relative signals from colour-sensitive cones, and more-sensitive but colour-blind rods in the retina also play a part. A night-time image appears less colour-saturated because the monochromatic rods supply a relatively stronger image. Subconsciously we calibrate the brightness of the ambience from that. Your video or film camera will record the same degree of saturation in dim light, which makes night look more like day than it does to the naked eye.
I guess we may also get feedback from the iris setting that the eye has achieved (it's harder to focus if your eyesight is failing a little).
>with film you have infinite control over the exposure time,
Yee..es, and that's how you get the flash-frame effect you mentioned, or time-exposure stills of night-for-day. But it's not infinite. There's something called reciprocity failure, which says that for very short or very long exposures you get a limiting return. In other words, two minutes isn't twice as much exposure as one minute. The silver halides spend so long waiting around for the next photon to arrive that they "forget" how much they've seen already.
Whether the eye has a variable time-exposure property, or whether it is purely an intensity-based response is a bit more complex. Let's not open that book this time.
>I'm all ears!
All eyes would be more useful
Group Technology & Services Manager
The Atlab Group
>at what light level does the
eye reach full aperture and begin to interpret >ambient light
Trying to compare any form of shooting to the human eye is like comparing a trip to the store for milk to a trip to the moon. Nothing does, can, or ever will come anywhere near the human eye in terms of the way it sees, and more importantly how the brain interprets what it sees.
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