Test Your Knowledge

Depth of Field: Factors and Effects

• Depth of field (DOF) is the distance between the nearest and the furthest objects that are in acceptably sharp focus in an image captured with a camera.

• The DOF can be determined by focal length, distance to subject, the acceptable circle of confusion size, and aperture.

• Increasing the size of the aperture or increasing the focal length reduces the depth of field.

• Sensor size affects DOF in counterintuitive ways: decreasing the size of the sensor while holding focal length and aperture constant will decrease the DOF (by the crop factor).

• Precise focus is only possible at an exact distance from the lens.

• The acceptable circle of confusion is generally accepted as 0.25 mm for an image viewed from 25 cm away.

• Camera movements such as swivel and shift adjustments of the lens holder and the film holder can cause the plane of focus (POF) to swivel.

• Focus stacking combines multiple images focused on different planes, resulting in an image with a greater (or less, if so desired) apparent depth of field than any of the individual source images.

• Diffraction causes images to lose sharpness at high F-numbers, and hence limits the potential depth of field.

• Many lenses include scales that indicate the DOF for a given focus distance and f-number.

• The DOF beyond the subject is always greater than the DOF in front of the subject.

• For given near and far DOF limits, focus and f-number can be obtained through simple calculations.Understanding Depth of Field in Photography

• The f-number is smallest when focus is set to the harmonic mean of the near and far distances.

• In practice, this is equivalent to the arithmetic mean for shallow depths of field.

• The focus spread is the difference between the near and far distances.

• The blur disk diameter of a detail at distance x from the subject can be expressed as a function of the subject magnification, focal length, f-number, or the aperture.

• The blur increases with the distance from the subject.

• When the blur disk diameter is less than the circle of confusion, the detail is within the depth of field.

• The depth of field is shallower for wider apertures and longer focal lengths.

• The depth of field is deeper for smaller apertures and shorter focal lengths.

• The hyperfocal distance is the closest distance at which a lens can be focused while keeping everything beyond that point acceptably sharp.

• The depth of field extends from half the hyperfocal distance to infinity.

• The depth of field can be calculated using various online calculators or smartphone apps.

• The depth of field can be used creatively to isolate the subject or to keep everything in focus.