RIP: The 35-mm Slide and Its Use in Planetariums
RIP: The 35-mm Slide and Its Use in Planetariums
By Mitch Luman, Director of Science Experiences
During the period 1960-2000, 35-mm slides were the prevalent means of visual communication in most planetariums. According to Maryann J. Riker, curator at Lafayette Collage Museum, “The 35mm slide was once a powerful recorders of art, memory, and time”. Although the use of slides as a means of storytelling has since passed out of common usage, their once ubiquitous application in planetariums to teach and entertain was unparalleled just twenty-years ago.
During their heyday, thousands of these universal 2-inch x 2-inch cardboard or plastic frames were used in planetariums (including our own). Along with the projectors and lenses necessary to project them, slides were the number one means of getting imagery on the dome before video came along. Beginning in the 1990’s planetariums began the transition to digital video projection over slides. Kodak stopped making its signature Ektachrome film used in creating slides in 2013; therefore few star theaters use them today.
The process of using slides in a planetarium show was more complicated than simply dropping them into a projector. First, they had to be acquired. Luckily, show producers back in the day did that step for you. The shows arrived in boxes containing hundreds of slides, each numbered and with a script meant to be adapted for each individual planetarium theater.
Next, slides used in a dark planetarium had to be prepared in a way that your father’s vacation slides never had to endure. Rarely do astronomical objects have faint rectangles surrounding them. No matter how dark the area surrounding an object was on a slide (whether it be text, nebula, or galaxy), without special treatment, a GRIS, or Grey Rectangle In Space would be seen. This had to be dealt with, so many tedious hours were spent in the darkroom preparing individual slide masks to allow for the image to show, but not the background. A special high contrast copy film known in the industry as Kodalith, or its later incarnation LPD-4, was used for this purpose. Worse than the tedium of making masks, this type of film was notoriously insensitive to red colors, so any slide with something red in it had to be painstakingly masked out by hand using a tiny paintbrush and special opaquing paint.
At our Koch Planetarium during the period 1985-2013, we utilized a darkroom, complete with chemicals and a sink, to create our photographic LPD-4 masks. Slides would eventually be arranged on large light boards in order to organize shows. Only after the slides were properly prepared, organized and matched with a script and audio could they be placed in the numerous projectors which we utilized for shows. During its halcyon days, our former Koch Planetarium employed six main slide projectors and six auxiliary projectors to perform most programs. The projectors were turned on and off and advanced manually using analog, switch controls.
What used to take twelve projectors can now be done withatwo cinema-grade video projectors and computer software. Today’s immersive technologies allow audiences to be drawn into the programming in a way that always surpasses slide shows. We’re still telling stories in our planetarium. It’s just that now we’re using the technologies of today. It makes you wonder what we’ll be using in planetariums thirty years from now.
Only time will tell.