# What type of projection system is used in Brideshead Revisited episode 5?

In the beginning of episode 5 of Brideshead Revisited there is a scene where one of the characters uses a "Universal Projector" to show some slides. It can currently be watched here, about 2m30s in.

What's confusing me is there are a couple times when the projector slide is flipped over to show a new image, when I would have though the image would just end up upside-down.

(Not the best example since the gif only shows one projection but it's clear from the narrative that two are there.)

On closer inspection there's no room for a light to project from behind the slides and I'm not sure the slides are transparent.

Here again the slide is first rotated to put it upright, then flipped over to show a different image: https://i.imgur.com/LMuPoGV.mp4 (too big for SE)

What type of projection system is this?

• Perhaps a completely fictional one? On the other hand maybe the "cartridge" is split into sections, each of which holds an image, but e.g. only the "top" half is projected at any time, so flipping the cartridge is required to deal with the other half.... Jun 18, 2020 at 18:53
• Re, "I would have though the image would just end up upside-down." Assuming that card is opaque (read about "opaque projectors, in the answers below), then it probably has two different images on it—one on either side. Which way is "up" on one side of the card has nothing to do with which way is "up" on the opposite side. Jun 19, 2020 at 17:17

This is an opaque projector (Wikipedia). The image of the illuminated photo print, postcard, painting, etc., is projected through the lens to the projection screen. A slightly different geometry, for greater magnification, is used to project art onto screens or walls for tracing or copying the image. Artigraph is a brand of these copying opaque projectors.

According to the Wikipedia article, projectors used to be divided into two classes: diascopes, where light shines through transparent slides; and episcopes, where light reflects off opaque prints. Thus, opaque reflectors are also known as an episcopes.

Episcopic projection is much less efficient (i.e., requires a more powerful light source) than diascopic slide/transparency projection. And because the power of light sources directly corresponds to the heat produced by them (especially with the pure incandescent or flame generated light used back in the day), and the need to protect the opaque image from the generated heat, this limited the usefulness of episcopic projectors. For equivalent power light sources, opaque projectors were dimmer than slide projectors, and therefore could not accomodate larger screens so large numbers of people could view them without being too dim.

The site Luikerwaal.com is dedicated to Magic Lanterns (Wikipedia), with lots great examples, including several episcopes and epidiascopes (convertible, able to show opaque or transparent sources). Interestingly, they have an image of an old advertisement for a "post card magic lantern", suggesting that at the time of the ad, all projectors were types of magic lanterns.