Concept
Refractive index — where it appears
2 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
What a ray does at a surface
A pool looks three-quarters as deep as it is — but only if you look straight down. At sixty degrees the same bottom appears at half its depth, and at eighty at a fifth, which is why the far end of a pool looks shallow enough to walk in.
What survives a pane of glass
A slab of glass moves every point of a picture and moves no direction at all. So the camera recovered from a photograph taken through a display case is exactly the camera that took it — out of a picture in which nothing is where it was.
Named alongside it
The objects these essays reach for when they reach for this one.
PinholeApparent depthCamera calibrationCritical angleFocal lengthLateral displacementPlane of incidenceplane-parallel plateSnell's lawVanishing point