Depth of Field Explained

Why does a portrait at f/1.8 keep only about 6 cm of a face sharp, while a landscape at f/8 stays crisp for meters? The answer is depth of field. It is the band of distance in a photo that looks acceptably sharp. Four settings control it, and one short formula tells you exactly where it starts and ends.

What Is Depth of Field?

Depth of field is the range of distances in a photo that look acceptably sharp. A lens focuses perfectly on only one plane. Objects a little nearer or farther blur so slightly that your eye still reads them as sharp.

That tiny blur has a name. Each out-of-focus point becomes a small disk on the sensor, called the circle of confusion. As long as the disk stays below a set size, the point still looks sharp in the final image.

For a full-frame sensor, the common limit is 0.029 mm. That value is the sensor diagonal of about 43 mm divided by 1,500. Our calculator uses this same value, so the numbers in this guide match its results.

A shallow depth of field isolates a subject against a soft background. A deep depth of field keeps a whole scene crisp, from nearby rocks to distant hills. Neither is better, because each one tells the viewer where to look.

How Is Depth of Field Calculated?

You calculate depth of field in two steps. First find the hyperfocal distance H, then use H and your focus distance to get the near and far limits.

Use one unit, such as millimeters, for every value.

• Hyperfocal distance: H = f squared / (N x c) + f
• Near limit: near = s x (H – f) / (H + s – 2f)
• Far limit: far = s x (H – f) / (H – s)

In these formulas, f is the focal length and N is the f-number. The letter c is the circle of confusion, and s is the focus distance. When s reaches or passes H, the far limit runs to infinity.

The Four Controls

Depth of field grows in direct proportion to the f-number. It grows with the square of the focus distance and shrinks with the square of the focal length. Doubling the distance gives roughly four times the depth, and doubling the focal length gives about one quarter.

The fourth control is the circle of confusion. A larger allowed blur disk means a deeper zone. That limit depends on sensor size, print size, and viewing distance.

A Worked Example: 50 mm at f/8

Take a 50 mm lens at f/8 on a full-frame camera, focused on a person 5 m away. Here is the math with c = 0.029 mm.

First, the hyperfocal distance. Square 50 to get 2,500, then divide by 8 x 0.029, which is 0.232. That gives 10,776 mm, and adding 50 mm makes H about 10,826 mm, or 10.83 m.

Next, the near limit. Multiply 5,000 by 10,776 and divide by 15,726, which gives 3,426 mm. The far limit is 5,000 x 10,776 divided by 5,826, which gives 9,248 mm.

So the sharp zone runs from 3.43 m to 9.25 m, a total depth of 5.82 m. Only 1.57 m of it sits in front of the person. The other 4.25 m sits behind them.

Why Is More of the Sharp Zone Behind the Subject?

The sharp zone is uneven because blur grows faster for close objects than for distant ones. So the zone stretches farther behind the focus point than in front of it.

The split changes with distance. At normal shooting distances, roughly one third sits in front and two thirds behind. Up close, the split moves toward 50/50, as the chart shows.

How Sensor Size Fits In

Sensor size acts through the circle of confusion. A smaller sensor is enlarged more for the same print, so it needs a smaller blur limit. APS-C cameras typically use about 0.019 mm.

With the same 50 mm lens at f/8 and 5 m, APS-C keeps only about 3.83 m to 7.20 m sharp. Frame the same shot with a 33 mm lens instead, and the zone widens to about 2.93 m to 16.9 m. Our guide on how crop factor changes focal length and aperture explains that trade.

Mistakes to Avoid

Most depth of field problems come from a few habits. Here are the ones that cost the most sharp photos.

• Focusing on the middle of a group. About two thirds of the zone falls behind the focus point. Focus about one third of the way into the group so the front row stays sharp.
• Trusting the viewfinder. Most cameras show the scene at the widest aperture. The real zone at f/8 stays hidden until you check the photo or use a preview button.
• Forgetting that distance matters most. Distance works as a square. Stepping from 3 m to 1.5 m at f/2.8 shrinks the zone from 0.58 m to 0.14 m.
• Using one blur limit for every print. The 0.029 mm value assumes a normal print at normal viewing distance. Big prints viewed up close need a smaller value.
• Stopping down too far. Very small apertures deepen the zone but add diffraction blur that softens the whole frame.

Which Aperture Should You Choose?

Choose the aperture that covers the depth your subject needs, and no more. The table shows how much a 50 mm full-frame lens keeps sharp at 5 m.

For portraits, open up to f/1.8 to f/2.8 to blur the background. For groups and street scenes, f/5.6 to f/8 gives a zone several meters deep. For landscapes, use f/8 to f/11 with a wide lens.

Landscape shooters often go one step further and focus at the hyperfocal distance. Our guide to hyperfocal distance for landscape focusing covers that method. To test a plan before a shoot, enter your lens and distance into the depth of field calculator for near and far limits.

Common Questions About Depth of Field

References

This guide uses the standard thin-lens depth of field formulas with a 0.029 mm circle of confusion for full frame. Real lenses and personal sharpness standards vary slightly. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.