It's so much fun manipulating things, exploring and getting surprising feedback.

I know it's not really fair to compare this highly scientific masterpiece to the artistic flash websites of the past, but for me at least it immediately evokes the same feelings.

I am always on the lookout for the classic sin of making it look like electromagnetic waves wiggle in space like a snake. I know it's convenient to glue the tangent space to the underlying physical space, but I think it confuses students.

To be clear: the amplitude of the electric and magnetic fields (and hence their components in each direction) oscillate in space/time. Any particular wave though should travel in a straight line (usual caveats apply). Of course you may incidentally also get e.g. sinusoidal variations in intesity perpendicular to the wavevector, but that will be because of the overall beam characteristics.

I don't mean to say I know a better way to show this, and I am aware of many complicating factors. I just think lots of people (my former students and self included) can come away with a wrong idea about how these waves work.

First, light apparently slows down in some materials because the photons are constantly interacting with electrons, and these interactions create secondary waves that are slightly out of phase with the original light. The end result is a modified wave that effectively travels more slowly. So light going in a straight line through air travels more quickly than light going through a lens.

Second, getting more into quantum physics, light typically follows the shortest path from one point to another because that path tends to provide the most constructive interference between different possible routes. (The "why" of this is more involved; Feynman's book QED gives a good intro.)

Third, if you imagine a lifeguard running to rescue someone in the ocean, then they will take the fastest path, which is not directly toward the person in the ocean. Rather, they will run a bit more on the beach in order to have to swim less because travel through the water is slower. The end result is piecewise linear = two straight lines of travel, with a bend at the water line.

To summarize, you can ask "_why_ does light bend going into and out of lenses?" and the answer involves seeing light no longer as a particle but as a wave function (the quantum perspective), and then taking advantage of that wave function's tendency to prefer fastest-travel paths, and then noticing that the apparent bend is in fact the path of fastest travel.

Cameras and Lenses - https://news.ycombinator.com/item?id=25357315 - Dec 2020 (213 comments)

(maybe we already can, I'm simply asking)

Most people who are smart and creative are nowhere near as productive. And most people who are extremely productive don't get sidetracked by side projects.

The way he builds up the mental model from a simple photon bucket to a pinhole and finally to a lens system is just incredible. I particularly loved the section on the circle of confusion. I've read dozens of explanations on depth of field, but being able to interactively drag the aperture slider and see exactly how the cone of light narrows and the blur reduces makes it click in a way that static text never could. This really should be the standard for digital textbooks.

Makes me wish for a similar resource that would teach 3+ element optics, moving elements, and sortof get closer to modern lens design.

Thanks for sharing it!

Some discussion then: https://news.ycombinator.com/item?id=25357315