# Cassegrain reflector

> Light hits a concave primary, bounces off a convex secondary, and focuses back toward the front.

**Laurent Cassegrain** · 1672 — Journal des sçavans

A letter signed L. Cassegrain described a concave primary and a convex secondary that sends the beam back through a hole in the primary. The tube is short for its focal length. Newton published a sharp reply about spherical aberration; the name still stuck.

Who Cassegrain was is still a bit thin. The layout is not: Hubble’s main optics are a Cassegrain cousin. This bench stops the return beam on a meter just ahead of the primary.

## Sources

- [Cassegrain reflector](https://en.wikipedia.org/wiki/Cassegrain_reflector)
- [Laurent Cassegrain](https://en.wikipedia.org/wiki/Laurent_Cassegrain)

## Links

- [HTML](https://www.loomrume.com/examples/cassegrain-reflector)
- [Open in Studio](https://www.loomrume.com/studio?template=cassegrain-reflector)
- [llms.txt](https://www.loomrume.com/llms.txt)