Hang around photographers long enough and you will hear, “I shot that wide open.” Or, “I had to stop it down to get that shot.” What they’re talking about is aperture.
Let’s review.
Aperture is the opening in your lens that lets light into the camera and onto the sensor. Together with shutter speed and ISO, aperture is an important factor in getting the proper exposure. The aperture, also known as f-stop, is also one factor in controlling how much of the scene is in focus. That’s called Depth of Field. More on that later.
Shopping online for a new lens and seeing the different choices can be intimidating. What does f/1.8 mean? Why is another lens listed as f/5.6? And what the heck does 18-300 mm f/3.5-6.3 really mean?
Let’s break it down.
Another important term to throw in now is focal length. Think of it as the field of view. A wide angle lens can have a focal length of 18 mm. A telephoto lens, 300 mm. If you use a lens that has a focal length of 50 mm, that's about what a human eye sees.
Now back to aperture.
When you see a number on your lens like 1.8, 5.6 or 6.3, that’s the maximum aperture for that lens. I did say maximum aperture. That's because your lens can be stopped down from there. It is very likely that your lens can be stopped down to f/22.
Here’s a few more important things to know.
The more expensive the lens, the more light it will let into your camera. A f/1.4 lens is always more expensive than an f/4 lens. And, the lower the aperture, the bigger the opening. So, an aperture of f/1.8 is a lot bigger than f/5.6. Take a look at this chart.
So now let's get back to your lens. If you see a label on the barrel with 35 mm 1:1.8, that means the lens focal distance is 35 mm and the maximum aperture is f/1.8. Remember, I said maximum aperture. Lens makers rarely talk about the minimum aperture.
Looking at our example of a 18-300 mm f/3.5-6.3 lens, we know that focal length is adjustable from 18 mm to 300 mm by rotating the barrel. So, this lens can go from being a wide angle to a telephoto.
We also know that the maximum aperture ranges from f/3.5 at 18 mm to f/6.3 at 300 mm. It lets more light in at 18 mm than 300 mm.
Is it making sense?
So what does shooting wide open mean? Shooting wide open means the photographer used a large aperture like f/1.8. The result is to bring the subject into sharp focus while blurring the background. Shallow Depth of Field.
On the other hand, shooting stopped down means using a small aperture like f/22. Landscape photographers shoot stopped down when they want to get the foreground, middleground and background in focus. Large Depth of Field.
All that, and we didn’t talk about a kit lens, fast glass or even hyper focal distance.
