diascope

noun3

1. •
   A projector used for projecting transparencies.

   • The diascope test pattern reference for automatic setup is a transparency (Figure 3), built into all TK47B lenses. — 1982
2. •
   a slide viewer, a device for looking at small transparent images.
3. •
   A flat piece of glass or transparent plastic, used to examine lesions in the skin

   • The diascope (a flat piece of glass) was used to press out the blood and expose the apple-jelly points of marginal growth. — 1898