1/30, 1/20 or 1/50?

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

> Dr. George A. Themelis  writes:
>
>Larry says that he likes working with more deviation than the 1/30 rule,
>closer to 1/20 that works well (better?) for computer screens.
>
>>I've heard (here on the list : -) that this rule is a variable one and
>>generally ranges from 20:1 to 30:1. If you enjoy looking at things from 7
>>feet away then 30:1 is a good rule. I generally want to look at *things that
>>I like* from a closer perspective so would choose to work on the 20:1 side
>>of the scale for objects or arrangements and the other side for landscapes
>>etc.
>
>The rule aims at a certain on-film deviation so if you shoot objects closer
>than 7 feet you might want to shift *less* (1/20 is more than 1/30) if you
>plan to include infinity.

********************  In reality the amount of shift should always be
determined by the main subject of the picture and obtain the best stereo
base for that presentation. Shooting closer than 7 feet does mean shifting
less than for objects or scenes farther than 7 feet but the amount of shift
should be sufficient to produce a reliable amount of on film deviation. The
1/30 rule produces only the smallest of deviations for the scene and
anything longer than that tends to be visible as cardboard cutouts at
different depths but not enough parallax to see contours of objects.

>
>Those concerned with big screen projection are usually more conservative
>and go for even less than 1/30, typically 1/50.  Stan White confesses 
>using 1/50 in his table-tops close ups and one of his justifications
>for doing so is that more depth is not always more desirable.

**********************  Not too long ago I saw some projected 3D slides that
were done with side by side SLR's so anything close to the camera was
somewhat Hyper. This was not true for objects and scenes farther away from
the camera. Despite the wide stereo base, people standing in the image at
some distance from the cameras definitely had the cardboard cutout
appearance. There was parallax to tell that one was standing in front of
someone else but not enough to determine that one shoulder was in front of
the other one. If these scenes had been shot with a 1/50 rule, it would have
been FAR worse. If conservative is 1/50, then it's no wonder to me that I
find so many stereo photos quite unsatisfying in a stereo sense. I think
that this factor is one that the public reacts to as well by seeming
unimpressed with many stereo photos. I understand the distortions that
happen between shooting and projecting an image, but a 1/50 rule just
doesn't produce stereo that I like to look at. 

>
>I understand how for computer work you might want more deviation.  But
>if you plan to project those images in a large screen stereo projection,
>you might want to consider 1/30 or less.  Is this an area where computer 
>3d and stereo projection have a conflict?
>
>George
>

Yes, perhaps a conflict in a sense, but I maintain that photos with a ratio
significantly lower than 1/30 are so unsatisfying in their basic geometry as
to be at best borderline stereo photos to begin with regardless of
projection/viewing mode. (except very large projections) This is my personal
preferrence and after hanging out on P3D I now understand the relationship
of these ratios and that some have very strong feelings different from mine.
However, in terms of getting the public to be impressed with 3D, the general
rule should be to use as much on film deviation as is practical without
creating undue distortions (dependent on viewing method). For best results,
you may not get every stereo photo to translate to a computer screen, but
the best of them (ie: reasonable amounts of parallax) will. Keep in mind
that the discussion of computer 3D isn't for the purpose of just promoting
computers, it's to help those who wish to put some of their camera work on
the computer or internet. As always, your most important output format will
determine what methods are best. If you shoot for projection, then you may
want to take extra photos for your web page that have a slightly different
geometry.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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