Depth of Field and Hyperfocal Distance for Film Cameras

Depth of field is the range of distances that look acceptably sharp in a photograph. Most film lenses have a scale engraved on the barrel that shows it directly, which makes techniques like zone focusing and hyperfocal focusing faster on film cameras than on many modern ones.

What controls depth of field

• Aperture: smaller apertures (larger f-numbers) give more depth of field. f/16 holds far more in focus than f/2.
• Focus distance: the closer you focus, the shallower the depth of field. Close-ups and macro have very little.
• Focal length: at the same subject size in the frame, depth of field is roughly similar; but from the same position, a longer lens gives less.
• Format: to frame the same scene, larger formats need longer lenses, so at the same f-number they give less depth of field. A portrait at f/2.8 on 6x7 looks much shallower than on 35mm.

Depth of field extends about one third in front of the point of focus and two thirds behind it at normal distances, becoming more even at close range.

Circle of confusion

Sharpness is a matter of degree. A point that is slightly out of focus records as a tiny disc; if that disc is small enough to look like a point at normal viewing size, it counts as sharp. The largest acceptable disc is the circle of confusion, conventionally about 0.03mm for 35mm, 0.05 to 0.06mm for 6x6 and 6x7, and around 0.1mm for 4x5. Depth of field scales and tables assume these values; if you make big prints and view them closely, stop down one stop more than the scale suggests.

Reading a depth of field scale

On a manual-focus lens, pairs of aperture numbers sit on either side of the focus index. After focusing, look at the distances opposite the pair for your aperture: everything between them will be acceptably sharp. On a 50mm lens focused at 5 meters at f/8, for example, the scale shows roughly 3.5 to 10 meters. SLRs with a depth of field preview button let you see the effect, though the viewfinder gets dark at small apertures.

Hyperfocal distance

The hyperfocal distance is the focus setting that gives the most depth of field at a given aperture. Focused there, everything from half the hyperfocal distance to infinity is acceptably sharp. It is calculated as:

For a 35mm lens at f/11 on 35mm film (c = 0.03mm): 35² ÷ (11 × 0.03) + 35 ≈ 3,750mm, about 3.7 meters (12 feet). Focus at 3.7 meters and everything from about 1.9 meters to infinity is sharp.

With a depth of field scale you don't need the formula: turn the focus ring until the infinity mark sits opposite your aperture number on the far side. The near distance opposite the same number on the other side is where sharpness begins.

Zone focusing

Zone focusing means presetting the focus to a distance and relying on depth of field instead of focusing for every shot. A street photographer with a 35mm lens might set f/8 and 3 meters (about 10 feet), giving roughly 1.9 to 7 meters in focus, and simply shoot. With a 28mm lens at the same settings, everything from about 1.6 meters to well beyond 30 meters is sharp. It works especially well with rangefinders and scale-focus cameras, where focusing every frame is slow.

Large format and the plane of focus

On a view camera, depth of field at a usable aperture is often too shallow to hold a whole landscape. Instead of stopping down to f/64, photographers tilt the lens so the plane of focus lies along the ground. That is the Scheimpflug principle.

Diffraction

Stopping down increases depth of field but eventually softens the whole image, as light spreads at the edges of a small aperture. On 35mm, sharpness typically peaks around f/5.6 to f/8 and softens noticeably past f/16. Larger formats are enlarged less, so f/22 on 6x7 or f/32 to f/45 on 4x5 remain usable.

All the guides are on the Learn Film Photography page, and every term is in the glossary. Shot something on film? Share it in the gallery.