P3D 3D realism and focus cues

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Sat, 17 Jan 1998 19:34:50 -0700
>From: "Greg Wageman" <gjw@xxxxxxxxxx>
>Subject: P3D Re: 2519 - focus (Dr. T)

>From: Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
>>I was repeating an indirect statement made by someone else but, yes, I am
>>certain about this.  When we "pay attention to" something, the eyes
>>perform two functions:  First they converge at this something, second
>>they accommodate (focus on it).

>But, George, you're ignoring the depth of focus of the human eye.  In full sun,
>the pupil diameter is very small (I don't know what the equavalent f-number is,
>but I'd guess it's large).

If all scenes are bright-sunlight scenes, and if everything is kept pretty far
away from the camera, then assuming no change in focus with distance is a
pretty good approximation. But those conditions do not always hold.

Another "realism" issue - it has been reported on P3D that humans apparently
use chromatic aberration in the eye (when the colors in the scene make it
available) as a feedback mechanism to achieve focus. Does the aberration
profile (degree as a function of distance from optimum focus) of a 3D camera
lens (or camera-viewer / camera-projector combination) match closely to that
of the human eye? In any event, the aberration degree and direction (if any)
are "frozen" in a still photograph.

Another possible issue - depth of focus as a function of brightness of
illumination of the scene [Note]. (Though if you're looking at the depth
that was in focus in the original photograph, it might match up.)

[Note: In some of the old 2D movies that are broadcast on television, there
are certain scenes which appear to be intended to depict outdoor nighttime
scenes (cues from story line and darkness of the scene), but which appear
very likely to be daytime scenes (sharp vertical shadows, maybe even cumulus
clouds), shot with a dark filter in front of the lens. They look so 
unconvincing by modern standards as nighttime scenes, I'm not even sure 
that's what they were intended to be. Have others noticed this effect in 
old movies? I wonder what cinematic techniques now in use will be chuckled at 
50 years from now. :-) ]

John R


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