Schlieren Mirrors: Spherical vs. Parabolic

Both spherical and parabolic mirrors are used in schlieren systems, but which one should you use and when? In this video, we'll look at how the two mirrors reflect light for two scenarios:

1) How does the mirror reflect the light when the incident rays are collimated (parallel)?
2) How does the mirror reflect the light when the incident rays emanate from the 2f point?

We'll see why the spherical mirror is ideal for the double-pass system, while the parabolic mirror is ideal for the Z-type system, but also why you can use either mirror in both systems without much loss in quality.

===== RELEVANT VIDEOS =====
► How To: Build Your Own Schlieren Setup
   • How To: Build Your Own Schlieren Setup  

===== NOTES =====
All simulations assume on-axis performance, even though in the schematics I show, the light source is located off-axis. If you want to use a beamsplitter for the double-pass system, then you would have on-axis light through the system.
I'm aware the spherical mirror focusing issue is called spherical aberration. Sometimes I deliberately choose not to include terminology depending on the intended audience of the video.

===== RELEVANT REFERENCES =====
Any optics book