Autostigmatic microscope and how it works

The autostigmatic microscope (ASM) is ubiquitous in the applied optics community and so familiar to those who regularly use it that it is barely mentioned in the literature. In some well-known applied optics books, the ASM's use is implied without ever being explicitly acknowledged because the authors assume no explanation is needed. However, each new generation of optical engineers need to be made aware of the workings and usefulness of the ASM, a tool every bit as useful as an autocollimator or alignment telescope. This note is an attempt to do just that.