Mirror

The object being observed has to be slim enough to allow light to pass through so it can be seen through the lenses. Originally, the object would be lit by shining sunlight directly onto it. Over time, sunlight or candlelight reflected in a plane or concave mirror would be used instead.

Originally, mirrors had a single plane face. They later had 2 faces that could be alternated: a plane side for working with low-power lenses, and a concave side for higher power lenses and light sources that were very close. Mirrors were held by a frame, which was usually round and fixed below the stage. They could be moved and rotated to show a particular face.