APERTURE & F-STOPS

Slr Side Profile

Above is a graphic of a side profile of a typical SLR (single-lens reflex) camera, with the lens pointing toward the right. The two small black lines represent the outer openings of the aperture. Since this is a profile graphic, it’s a little difficult to understand what the opening actually looks like, so the graphic on the next page shows the head-on view of a lens aperture.

Lens Apertures

As you can see, for each diameter of aperture there is a corresponding “f” value. The chart lists all “common” aperture values, as denoted by the corresponding f-values. Between each of these values, most modern cameras will allow you to set values 1/3 of the way between. For example, between 5.6 and 8 there is f/6.3 and f/7.1, too. The “whole” stops of f/5.6 and f/8 have two in-between points that you can dial your camera for.

The key to understanding this all right away is to immediately disregard these numbers as any sort of actual numerical value in relation to one another. In other words, do not start mentally comparing these whole numbers to decimals or trying to make a relationship between these numbers using math. Rather, you’re going to need to memorize each of the f-values (aka “f-stops”) as categories. Just like you would memorize your ABCs from A to G, so should you memorize these numbers (f/2 to f/16).

So, you ask, if I’m to memorize these numbers, what is the significance of all this? Glad you asked. As you can see, the lowest f-stop number, f/2, is the widest opening in the aperture. This means that you are letting more light reach your sensor than f/2.8. Just like a water pipe with a wider diameter allows more water to flow through per second, so does a wider aperture when it comes to letting more light “flow” into the camera’s sensor.

The numbers in the above chart are there for a reason. It certainly seems arbitrary to have these seemingly obscure numbers jumping from 2 to 2.8 to 4 to 5.6 to 8, then 11 and 16. How are these all related? Simple – each “stop” (just a basic term – memorize this jargon, too) going from 2 to 2.8 and then to 4 is allowing half the amount of light into the sensor. Higher