Use a wider Aperture?

We have all been read, online tutorials,  videos and other photographers "Use a wide Aperture..." but it lacks content.

To help you to understand all the variables here is a lesson for your camera and lens. Rather than giving people a calculator, have them discover it.

The key lesson is this:

Depth of field is not determined by aperture alone. It also depends on focal length, camera-to-subject distance, sensor size, and the acceptable circle of confusion. Change one variable and the result changes.

Exercise: Measure Depth of Field Yourself

Equipment

Camera

Zoom lens (variable-aperture lens is even better)

Tripod

Tape measure

Yardstick or measuring tape extending away from the camera

Small object to focus on

Remote release or self-timer

Setup

Place the camera on a tripod.

Put the subject exactly 10 feet (or 3 m) from the camera.

Lay a tape measure on the ground extending beyond the subject.

Focus precisely on the subject.

Use manual focus so it never changes.

Turn off image stabilization.

Test 1 – Aperture Only

Without moving the camera or zoom ring:

f/4

f/5.6

f/8

f/11

f/16

f/22

After each photograph determine:

nearest readable number on the tape

farthest readable number

total depth of field

Record the results.

Aperture

Near Limit

Far Limit

Total DoF

f/4

f/5.6

f/8

f/11

f/16

f/22

Test 2 – Change Focal Length

Now repeat at:

24 mm

50 mm

100 mm

Keep the camera in exactly the same place.

Most photographers will immediately notice that the longer focal lengths produce much shallower depth of field.

Test 3 – Keep Subject Size Constant

Now comes the interesting part.

Suppose your subject fills the frame at:

24 mm from 6 feet

50 mm from 12 feet

100 mm from 24 feet

In each case, adjust your distance so the subject appears the same size in the image.

Many photographers are surprised to discover that the depth of field is much more similar than they expected. This helps separate the effects of focal length from the effects of camera distance.

Test 4 – Variable Aperture Zoom

Now repeat with a common lens such as:

18–55mm f/3.5–5.6

100–400mm f/5–6.3

Notice:

At the wide end the lens may open to f/3.5.

At the telephoto end the largest aperture may only be f/5.6 or f/6.3.

Ask yourself:

Did the smaller maximum aperture increase depth of field?

Or did the longer focal length decrease it?

Which effect dominates?

This demonstrates that a variable-aperture zoom changes two variables at once, making it harder to predict depth of field without understanding the underlying relationships.

Questions

Instead of telling readers the answers, ask them:

Did stopping down always increase depth of field?

Was f/22 always the best choice?

At what point did diffraction begin reducing image sharpness?

Which had the biggest effect:

aperture

focal length

subject distance?

Can you now explain why someone cannot answer the question:

"What aperture should I use?"

The Takeaway

This exercise reinforces one of the central ideas behind Practical Photography by Larry:

There is no "correct" aperture. There is only the aperture that gives enough depth of field for your intent.

The answer isn't "use f/8" or "always shoot at f/11." It begins with Why are you making this photograph? Once you know the intent, aperture becomes a deliberate choice rather than a rule. That fits well with your recurring theme that photographers should understand the why, not just copy camera settings.