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Characteristics of the Human Eye

Joe G.

Joe G.

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So I'm writing a film noir, and suddenly a bunch of threads and articles seemed to mesh together...

1. Shooting mostly on one lens.

2. Having it the same as what the human eye would perceive (voyeuristic POV).

3. Figuring out what focal length, format, framing to use.

So here's what I came across:

ClarkVision

"Image focal length of the eye = 22.3 mm"

This led to a question about how this translates to a given film/sensor area size.

Facts and Figures concerning
the human retina

"Size of the retina.

* 32 mm from ora to ora along the horizontal meridian (Van Buren, 1963; Kolb, unpublished measurements). Area of the human retina is 1094 square mm"

This goes to the FF35 v S35 debate, but also to the exact framing. For a 2.40 :1 wide framing ratio (here's where you guys come in) -- What would be the closest match to what a normal eye would see, given the above data?

Any thoughts on doing a whole feature on such a lens? I intend to use some black and white, and then transform to color several times, limited locations, low budget.
 
Take a look at this:
http://www.rags-int-inc.com/PhotoTechStuff/CameraEye/

Perception

Another difference is that the image plane on our retina is semi-spherical, not flat as it is with film or digital photography. The small area covered by the macula determines the angle of view of our central vision. Within this an even smaller area, the fovea, determines how we focus. The rest of the retinal area determines the much larger angle of view of our peripheral vision. And we use two eyes to form a single image. In general our peripheral vision is less sharp and less color sensitive. But our brains are very sensitive to distance and motion in this area. We select camera lenses based on their relationship to the angle of view based on our central vision. We call them wide angle, normal, or telephoto based on the angle of view in the captured image. We sometimes stitch or combine multiple digital images together to accomplish impressively wide angle views called panoramas. In a similar fashion, the brain uses information from each eye to expand our peripheral vision, add depth, and fill in the blind spot at the optic nerve of the other.

Precisely measuring the normal angle of view is difficult. It is usually based on the horizontal or diagonal angle of view. For normal central vision, this will be approximately 50 degrees, but our peripheral vision expands this to 120 degrees. The focal area (under the fovea) is less than 2 degrees. For a camera, the angle of view is a function of both the lens focal length and the size of the image plane. So the proper lens will vary with the image format. A simple test is to look at the image in the camera’s viewfinder and again with the unaided eye. The normal lens will produce a similar perspective or field of view. Just for reference, the focal length of the lens and cornea is about 22 mm.

----

That's the problem with the whole concept of "normal" view -- a camera has a frame in which reality is bordered and our eyes do not perceive a frame.

Therefore you get into the basic conflict, which is what lens produces the most neutral or "normal" perspective and what matches our human field of vision. The first tends to be a longer focal length than the second.

These issues are more easily resolved in very large projection systems like IMAX where you can use very wide-angle lenses with the image projected very large so that your eye is concentrating on the center of the screen which has a more "normal" perspective yet there is a lot of peripheral vision being stimulated.

The closest thing to this in a normal movie theater is scope projection on a fairly large screen if you sit close enough. In that case, I find that the 50mm anamorphic lens is ideal (which would be a 25mm lens in Super-35 cropped to 2.40) because you've got the vertical perspective of the more neutral 50mm lens yet the expanded horizontal view of a 25mm lens.

In standard 16x9 or 1.85 photography using a 35mm-sized sensor, I find that the 40mm lens tends to seem the most neutral in perspective, yet a 27mm to 35mm seems better-suited to showing off a space with an adequate field of view.

Truth is that to match the total human field of vision, 120 degrees, you'd need a 6mm or 7mm lens in 35mm cine photography, which looks ridiculously wide-angle. For a 50 degree view, that would be more like a 27mm lens.
 
David,

How would your choice change from Super 35 to shooting on the FF35 new Scarlett:

"The closest thing to this in a normal movie theater is scope projection on a fairly large screen if you sit close enough. In that case, I find that the 50mm anamorphic lens is ideal (which would be a 25mm lens in Super-35 cropped to 2.40) because you've got the vertical perspective of the more neutral 50mm lens yet the expanded horizontal view of a 25mm lens."

If it was still anamorphic but on the larger sensor -- is there an anamorphic lens at that focal length that covers the required area?
 
I don't think an anamorphic lens would cover the 24mm height of the FF35 sensor - they are designed to cover the 4-perf 35mm height, which is 18.59mm. But it may come close, who knows. I'm sure someone is going to try it.

Depending on how much of the lens coverage is useful, on the larger sensor, the same focal length is going to appear more wide-angle, so you'd use something longer to get the same field of view. Probably you'd use the 75mm anamorphic to get a similar effect of the 50mm anamorphic.

But with a 6K FF35 sensor, more people would probably use a spherical lens and crop to get 2.40 because even then you'd have a lot of resolution. Since there is a 1.5X magnification factor, if you were going to use a 25mm lens in S35, you'd use a 37.5mm lens (or the closest thing, either a 35mm or a 40mm lens) to get the same field of view.
 
A lot of anamorphics don't have a great minimum focus, though there are close-focus versions of some series, like a Close-Focus Primo. There are specific macro lenses in anamorphic too, though most are just rear-adapted spherical macros.

It's one of the things to check when renting anamorphic lenses, what the minimum focus is. Otherwise you can get stuck, like when you rent a 150mm anamorphic with a 7' minimum focus and it isn't tight enough, and you switch to your 100mm anamorphic with a 5' minimum focus and find it's the same size image. Like I said, some series are better than others in that regards.

I'd assume that the longer anamorphic lenses will have a larger coverage area, probably enough to cover the 24mm height of a FF35 sensor.

Actually maybe I'm wrong... maybe most anamorphic lenses would cover that height if they normally can cover a 21mm to 24mm width. Not sure if the image coming out of the back of an anamorphic lens is a circle or an oval though...
 
I believe when ID Software created the first version of Quake, a 90 degree angle was used for player vision, whilst A.I opponents got 120, to help make up for being violent, but stupid.

Its somewhat subjective, and I (like my "ex-fighter pilot"/"Top Gun" father :) ), have a left eye that pans constantly, and rapidly, from left to right, at all times? something we both discovered during independant trips to the opticians. Still got 20:20 though, apparently.

Not sure I like being a clone though :shiftyph34r::ph34r:(I will resist!)
 
I'm sure others can pitch in, but I understand the human vision to have other characteristics too. First one being if you're focused on something with a 'fixed' stare, your eye only has about a 6 stop latitude.
It gets a ~20 stop latitude with a combination of adjusting it's iris and chemical control of receptors. i've always thought it a little unfair that other imaging systems systems i.e film, digital, art...have to display the entire latitude in the one static image.
The other thing is your eye has a limited angle of vision that is clear and in focus with the rest taken up with increasing blurred peripheral vision.
An ideal setup to reflect the HVS would be what David M mentioned above and an auto focus lens baby lens to reflect eye movement and fluid head/dolly to mimic head/body movement.

Dave,
 
I think perspective has more to do with what one would perceive as "normal" for the human eye than FOV. Depth perception and apparent visual distance between foreground and background elements in the composition. This is not necessarily uniform for different people. A lens in the 70-80mm focal length range matches my natural perspective pretty well with glasses on. But I am very near sighted.

It would be interesting to get feedback from others as to what focal lengths most closely approximate their perspective view compared to their own eyesight characteristics. Would someone who is far sighted have a shorter or longer focal length perception of perspective?
 
More than focal length

More than focal length

Red and Pink optical systems have many aspects in common. Support, pan tilt head, Lens, Iris, sensor, and brain.

In both red and humans, the sensor and the brain are a unit.

But the Human eye is an extension of the brain, just as the brain itself is an extension of the nose. The pinout of the retena does not mate to a connector in the brain. The signal is highly processed at the surface, and processing continues along the optic nerve.

One output of this processing is scores for qualities like Roundness, Triangularness, Squareness, Etc. We are amazingly good at detecting differences in roundness, it is how we know where someone is looking.

Edges too. Human brains love edges. I'm guessing that's why wavelet encoding works, and why we prefer edge enhanced images for viewing.
 
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