In Jonathan Crary’s “Techniques of the Observer,” he discusses “retinal afterimages,” and how they were no longer seen as optical deception, but rather as truth. In other words, what was seen was to be believed. He illustrates various different optical devices, including the stereoscope and the kaleidoscope. The kaleidoscope uses mirrors to create a symmetric, geometric pattern composed of “reflections of itself.” Since symmetry is a large part of aesthetics, the kaleidoscope was seen as a type of art, one that humans could not recreate without years of trying. The stereoscope was a huge phenomenon during this time period, and was one of the main ways people experienced photographs. The stereoscope was the closest people had gotten to seeing real life within a photograph, as the function of the stereoscope was to make the image seem tangible and like natural vision. 

Most of these devices were used for at-home entertainment, so it is safe to assume that the owners of them were at least middle class, and rich enough to afford them. This suggests that its users were mostly white. Most of the devices were used to entertain all ages, but the kaleidoscope especially appealed more to children than adults. As the devices were used in the home, it is likely they were in rooms meant for entertainment, such as living rooms or parlors, and used within a group of people. Each device requires a different method of use. For example the kaleidoscope necessitates some form of light, so an observer will often hold it up to light. 

The stereoscope did not pose an illusion of motion, but still “reorganized” the observer in order to work. It is greatly connected to binocular disparity, though, as it is this that causes the perception of an image to change and seem tangible within the stereoscope. The viewer sees depth from the two images, and what they see is more of a “conjuration,” rather than an image. Retinal afterimage was important especially for the thaumatrope, which deceives the viewer into seeing motion. The thaumatrope also utilizes persistence of vision, as the images one sees blend together to form the illusion of motion. All of these devices rely on tricking our vision in order to create an illusion, and this begs the question: How much can we really trust our vision?