"Somehow the glasses "gather in" the image -- even on a huge Imax screen -- and make it seem half the scope of the same image when looked at without the glasses. "
- Walter Murch
In most circles of 3D film making it is understood that miniaturization is easy to increase or decrease in camera. Some people even know how to use this to their advantage. Very few people understand how miniaturization works, or the scope of the anomaly. Because of this, unwanted miniaturization makes its way into 3D movies, distorting the observers experience. The fact that something looks smaller than life on an IMAX screen is very disturbing considering the film maker had to choose that apparent size during production. Walter Murch should have taken this opportunity to explain how to compensate for this condition in camera. Decreasing camera interaxial will increase apparent size. Calculating the correct interaxial spacing and apparent size is determined by the ratio of viewer interocular to camera interaxial. Because so few people understand miniaturization it is often overlooked in popular 3D educational seminars. Sometimes this calculation takes a back seat to insignificant stereoscopic anomalies (like edge violations). I have even heard some say choosing interaxial spacing is a creative decision, and there is no math involved. Unfortunately that means your teacher is just guessing.
Even Academy Award winning film makers need to learn the basics of 3D and how it looks on the big screen. Not write off things like miniaturization which they do not understand. Improper image size is completely within the scope of the film makers creative decisions. Script supervisors need to take detailed notes about camera interaxial and lens focal length. Editors need to understand these measurements so that they can choose better quality 3D shots, and take into consideration the intended size of objects when editing. Two clips may have the same screen size, but have completely different apparent sizes to the observer. That calculation is falling into the hands of untrained "Rig Techs" who are given the critical job of pulling interaxial distance.
The 3D educational community needs to focus on teaching seasoned film makers how to compensate for the issues like the ones contained in this article in order to bring 3D film quality to a point where it is accepted by the masses.
Let me back up what I am saying by referring to a quote from Hugh Murray's 1995 document ...
IMAX® 3D Film Production
An Overview of 3D Photography
Presented at The Workshop - ISTC 1995.
"In 2D photography, longer focal length lenses make the images larger. In geometric terms this is not true in 3D. The apparent size of subjects compared to their "real" size is determined by the ratio of viewer interocular to camera interocular and nothing else. Larger camera interoculars make things appear smaller and vice versa."