Sometimes, weird things happen to light when it travels through glass.
Just look at the cover of Pink Floyd’s Dark Side of the Moon for an example. When light shines through a prism, you can see the spectrum of colors. You can actually see a lot of things if you listen to that album correctly, but let’s not go there.
Of course, glass is used in camera lenses. In photography, the job of a lens, as you know, is to focus light on to your camera’s focal plane (the sensor or film). But sometimes lenses have problems focusing all the colors that are magically contained within a ray of light to a single point on the sensor. Some colors of light, like blue, tend to refract (bend) more than others, like red.
When this happens in photography, and screws up your shot, it’s called chromatic aberration, and it can be depicted in a very simplified way like this:
Chromatic aberration (CA) causes “color fringing” in a photograph. An unwelcome purple (or sometimes green, or even red) fringe of color appears along the high-contrast edges in a photo. CA could occur with practically any lens. Some lenses use “low dispersion” glass to minimize CA. It’s most common (or so I’ve read) in zoom lenses with a variable aperture.
I thought I had a good example of CA to share with you. But after combing through my archives, I couldn’t find any. I’ve definitely seen it happen in my own photos though. Fortunately, many photo editing tools (like Lightroom, my tool of choice) can correct for it.
That’s all I can say about chromatic aberration. The optics and mathematical theory behind it can get complex. What I’ve said here represents the sum total of my knowledge on the subject.
What I do know is that photography is all about light, and the way light behaves is amazing. This is just one example. For better examples, read up on quantum physics. You’ll learn that light is both a particle and a wave, and it essentially moves independent of time, and light “decides” how it’s going to behave based on how we observe it. Sounds crazy, but it’s all proven science.
That all has nothing directly to do with chromatic aberration I suppose. But it’s really mind-blowing stuff, when you think about it.
Think about it while listening to Floyd and your head might literally explode.