Understanding Aperture: How to Avoid Blurry Images

by Kristen Duke ; Updated October 17, 2017

Taking pictures that turn out blurry is very frustrating. While you can correct lots of issues with software, there’s not a lot you can do fix a blurry picture — so it’s important to get it right when you take the shot.

Blurriness can happen for a number of reasons; a few weeks ago I wrote about how to avoid blurry images by focusing on the shutter speed. In today’s post, I’ll share tips about how to avoid blurry images by understanding your aperture.

When using manual settings, an important part of the exposure equation is setting the aperture, or f-stop. If you set the aperture incorrectly, the result will be blurry images.

For example, look at the picture of a flower at the top of this post. It is the same distance as the image below, but the background is blurred. This blur is intentional to make the flower subject stand out. In this case, the aperture was set to 1.8. While in the photo below, the aperture was set to 8.0. You can see the difference in the entire image blur.

Flower on a bush

Aperture affects how much light enters the camera. You change the value according to how light or dark it is to get that perfect exposure. The lower the aperture number, the more light is let into the lens.

But the lower the aperture number, the more blur occurs in the background of the image as well. Blur in the background is often what you want, and I’ll get into that discussion in a later post, when I talk about depth of field. To get the intentional background blur, and not the unintentional blur of your subject, you need to set up properly.

Since I photograph mostly people, this is very important to me as I don’t want to unintentionally blur the people I’m photographing. I cover this in my beginner book, Say NO to Auto, but I’ll share parts of it today.

Think of the aperture opening on a number scale of 1 to 10. At 1, you will have 90 percent of your image blurred, and only 10 percent in focus. Depending on what lens you are using, you can shoot at an f-stop of 1.4 to capture a small amount of the image in focus with the rest out of focus.

This approach makes a singular subject stand out much more — the focused subject contrasts to the background blur.

If you are photographing four people and want them all in focus, set your aperture up a bit higher than 1.4, close to a 3.5 or 4.0 to get the group all in focus, with some background blurred.

In the image below, I wanted both faces in focus, so set my aperture to 4.0.

Both faces in focus

When I set my aperture to 1.8, and set my focus on the girl, the boy is now out of focus.

Setting your aperture

You can always go as high as you’d like, up to f 6.0 or more, but your image will get darker, and the background will become more flat with less depth. Photographers often try to get away with as low an aperture as possible, depending on what they are photographing.

If you remember this tip when setting your aperture, you will be much happier with your outcome. You may want the background blur, as in the flower picture, to set your subject apart from the background. But when photographing people, you generally do not want one person blurry, or out of focus, so understand how aperture works to set it correctly.

Photo credit: Kristen Duke