Every time I come across one of Bartosz posts, I drop everything to read it. And I learn so much.
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.
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.
Can we donate to creative individuals like the OP so they keep making amazing stuff? This is the kind of output LLMs will not be able to produce any time soon.
I am amazed by people like Bartosz Ciechanowski and Andrey Karpathy. What would be a lifetime side project for other smart and curious people, they seem to release every quarter. How do they do it?
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.
> ̶P̶i̶c̶t̶u̶r̶e̶s̶ ̶h̶a̶v̶e̶ Art has always been a meaningful part of the human experience. From the first cave drawings, to sketches and paintings, to modern photography, we’ve mastered the art of recording what we ̶s̶e̶e̶ think and feel.
Cameras and Lenses and photography has been such a fascinating and open and do-it-yourself tinkering medium for well over a century: when are we going to get to be able to play around with what's inside iPhone, Samsung, and Pixel cameras?
Bartosz Ciechanowski's blog brings back the joy of surfing the web during the heyday of Adobe Flash (minus the 100% CPU).
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.
In case anyone is curious about _why_ light bends when it enters a lens:
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.
23 comments
[ 1.2 ms ] story [ 48.2 ms ] threadThe 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.
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.
Cameras and Lenses - https://news.ycombinator.com/item?id=25357315 - Dec 2020 (213 comments)
Some discussion then: https://news.ycombinator.com/item?id=25357315
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.
(maybe we already can, I'm simply asking)
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.
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!
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.