Aperture Labs

Today we're going to look at the aperture as it relates to the amount of brightness in our final image. There are other impacts of the aperture like depth of field, but that's a topic for another day. First let's look at what an aperture looks like:

Photo from Wikimedia Commons by User Mohylek.
Creative Commons Attribution-Share Alike 3.0 Unported License

The aperture is the metal blades in the lens. For this article we're going to consider that the aperture limits the amount of light that passes through the lens. (It does other things that we'll address in future entries.)  We refer to the size of the circle in terms of f/ number which is the ratio of the lens focal length to the size of the hole. A larger number is a smaller hole, which lets through less light. For a practical example, I made another animation.

As you can see, the smaller the number in the bottom right corner gets, the brighter our image. You can also use this information for selecting a lens for shooting at night. A lens with a smaller f/ number will let you shoot in darker conditions. As an example, if I take a f/5.6 lens* it will be harder to get bright exposures than with a f/1.8 lens.

* Lenses have two numbers when you're looking at them, one is the focal length and the other is the f/ number. That f/ number is the number of the lens when the aperture is fully open, or the maximum aperture / minimum f/ number. At some point in the future I'll write an entry about how the f/ number is derived.