A common question in online photo groups is, "How can I keep sharp focus on everyone in a group photo?" The answers often range between ill-informed and downright terrible.

• "Keep them close together in a single line"
• "Set your f-stop to the number of people in the group, ie: if there's 5 people turn it to f/5.6."
• "Put everyone on the same focal plane."
• "Keep your lens set between f/8 and f/11."

The Real Secret is Depth of Field

In reality, sharp focus is found in a specific distance range called "depth of field." Things too close will be out of focus. Things too far away will be out of focus. But things within your depth of field will be IN focus.

How deep is that field of focus? Is it half an inch? Ten feet? A hundred yards? It can be ANY of those depths! You can take a photo of a person with a mountain range miles away in the background and have everything in focus. Or, you can take a picture of a dog's nose and have his eyes be completely blurry. When you understand depth of field, YOU have total control over your photo's focus range!

How Do You Change It?

There are three things that affect how deep the field of focus is:
1) What your aperture (f-stop) is set to
2) How far away you are from the subject
3) What lens you're using

Let's use an example of a portrait. You're using a 50mm lens and are standing five feet away from the person.

Aperture

If you set your aperture to f/1.8, your field of focus will be about 3-4 inches deep. That means if you focus on the tip of their nose, their ear will be out of focus. Now set your aperture to f/11. This makes your depth of field two feet deep. The person will be completely in focus.

Distance

You can also affect it by changing your distance from the subject. Let's say you've got that first setup (f/1.8, 50mm lens, 5 feet away). Your DOF is 3-4 inches and it's not enough. If you back up to be 10 feet away, now your depth of field has expanded to 16 inches. That's enough to keep the person in focus and still keep everything in front of and behind them nice and blurry.

Lens

Lastly, you can change lenses. So you're still 5 feet away at f/1.8. But while the 50mm lens gave you 3-4 inches of focus, if you change to a 35mm lens, you'll have about 8 inches. Change to a 24mm lens, and you'll have 17 inches of focus.

Since changing lenses or your distance from the subject isn't always practical, the usual way to change your depth of field is to simply change your aperture.

The Short Version

To make your depth of field DEEPER:

• Make your aperture smaller (higher f/number)
• Change lens to a smaller focal length
• Increase your distance from the subject

To make it SHALLOWER:

• Make your aperture bigger (lower f/number)
• Change lens to a larger focal length
• Get closer to the subject

Try It Yourself!

To see how each of these affect depth of field, use a Depth of Field calculator and experiment by changing the settings. There are several phone apps which do it, such as PhotoPills. There are also a few free online versions. Try this one: Online Depth of Field Calculator

Once you understand the concept, getting good at it will just take practice. Start by taking the same shots with a deep range of focus and a shallow one. The more you do it, the easier it gets!