P3D Accomodation

[John Toeppen <toeppen@xxxxxxxxxxx>]

Gabriel wrote:

> My guess as to why is because of accommodation (eye focusing far or
> close). Even though it is a very weak way of determining absolute
> distance, I think certain individuals are more sensitive to it's
> effects. This is not to say they can resolve distances very well
> but they can tell if it is close or far away. Therefore in the
> case of viewers (2-D and 3-D) I (as also Paul does) doesn't get
> fooled that the distance is at the place the image suggests it
> is. For people that are not sensitive to accommodation they sense
> the image as if it was in reality.

Fourtunately, when an image is viewed as bright the eye stops down. 
Then critical visual focus is not so important.  A slide viewer can
create an "artificial infinity" if the slide is located at the focal
length of the lens.  Or the image may be made to appear at 15 to 5 ft if
the lenses are moved away from the slide.  The correct focus for a
viewer (for technical accuracy) should be where the primary subject
would actually appear.  A bright bulb (halogen or krypton) not only
gives a better color balance, but also stops the eye down making it less
sensitive to eye refocus cues, leaving only parallax cues.

I might suggest that you stand in front of a window and look out and
visually focus on an object twenty feet away.  Now hold the viewer up to
one eye and focus until the image and the world are both in focus.  Now
look into the viewer and adjust the interoccular until the convergance
is the same as it is for the real world.

I believe that there is a tendancy for people to focus so the slide
appears at 10 1/2", a zone of comfort for normal magnified viewing.  A
slide viewer is something else.

Keystone made viewers to "exercise" the eyes by focusing at infinity. 
Realist later made the same claims about adjusting one's eyes to
infintiy focus.  The claim was that after a long day of close work,
infinity focus was relaxing.  

Rich color, fine detail, large field angle, and far focus effects in
stereo fields create a single integrated effect: "Eyecandy."  This
effect is the motovation for "color quests" or other actions to acquire
"eyecandy" wherever you may find it.

Jon Siragusa posted some more of my JPS pairs at:

http://www.3dexpo.com/gallery_toeppen2.htm

John Toeppen
http://members.home.net/toeppen


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End of PHOTO-3D Digest 3118
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