balopticon การใช้

Opaque, " Balop " slides were cards on 4 " by 3 " stock or larger ( always maintaining the 4 : 3 aspect ratio ) that were photographed by the use of a Balopticon.
In the early days of television, there were two types of slides for broadcast a " transparent slide " or transparency, and an " opaque " slide, or " Balop " ( a genericized trademark of Bausch & Lomb's Balopticon projectors . ) Transparency slides were prepared as 2-inch square cards mounted in cardboard or glass, or 4 " by 3.25 " film, surrounded by a half-inch of masking on all four sides.