Скачать или смотреть WHY does aperture change depth of focus???

After getting some old cameras I was reintroduced to the idea of depth of field/focus. As a physics teacher my mind immediately started wondering WHY this worked. I found plenty of videos describing HOW adjusting f-stop affected depth of focus... but no real explanation as to why this works the way it works.

So, I made a video. It's sort of a boring video (I feel for my students now). But I think it does a decent job of describing the optics of depth of focus.

Optics App: https://phydemo.app/ray-optics/

Other good videos on the HOW:
   • A Simple Guide to Depth of Field  
   • Understanding Depth of Field: How Aperture...  

Chapters
0:00 Intro
00:51 Disclaimer
01:08 The HOW
01:50 The WHY
02:30 Lens Simulation
05:30 Two Sources
07:46 Recap