Cameras and Lenses

It's truly amazing to me how someone can be this talented. The text, the animations, the style. It's all high quality.

I'm in awe.

Looks like so, with a clever rotation, clipping, and drawing twice (had a cursory look at 'lenses.js', look for 'draw_blade')

I have a question for the more knowledgeable:

Color filters on the sensor split the light into three wavelength ranges - red, green, blue. Then photosites measure intensity of light, which means that sensor only knows that the incoming photon is "roughly green", but doesn't actually recognize its precise wavelength.

So e.g. when the light is pure orange, it falls down into red wavelength range and is counted as red.

Based on this I would expect that cameras would often produce pretty incorrect colors, but they are usually pretty good (after correcting for stuff like white balance).

You are right, this is a challenge. The wavelength of the light cannot be measured directly, only inferred by the intensity of the pixels with the different color filters. On the other side, most reproductions of photos are reproducing the original frequencies either. A computer screen has red, green and blue dots, which produce light at the corresponding wave lenghts. So if you have orange light, you have a signal on the green and red pixels and the green and red dots on your screen will light up. Which will be detected by the sensors for red and green light in your eyes. No where in the chain, not even in your eye, is a sensor for "orange" directly, it is just the mixture of the red and green sensitivity.

It is important to note, that neither the sensor pixels nor your eyes have a complete separate reaction to a wavelength. The sensitive area strongly overlaps. So for hues of green which have rather long wavelengths, you get some reaction on the red pixels, which gets stronger as you move towards orange, where both red and green pixels detect until it gets more and more red and less green. The exact absorption curve of the sensore color filters matters here, that is one reason, different manufacturers have slightly different color rendition. On top of that is calibration, when converting the raw image into a proper RGB-image, one can further balance the response. For that, the color calibration targets are used, which have like 24 patches of different colors. Taking a phone of this target, the calibration software can both calibrate for the light illuminating the target as well as the color response of your camera.

A common reason for red-green colorblindness is that the affected persons have the sensitivity between the red and green colors overlapping too strongly, so they loose the ability to differentiate. A green creates almost as strong a signal in the "red" cells. A way to improve the color vision for those people are glasses which increase that separation by absorbing the frequencies between the red and green colors.

The article is very good but you have to consider the existence of other filters, not only the Bayer one.

And the Canon Dual Pixel AF that works a bit different than the article explains https://www.canonwatch.com/dual-pixel-af-has-become-a-canon-... (but the substance is the same)