Depth of field

The Depth of field tool shows the sharp zone of the image for a focal length, an aperture and a focus distance, and what this setting produces: hyperfocal distance, background blur (bokeh) and diffraction. The top of the screen gives the result; four tabs detail each effect: Hyperfocal, Inverse calculation, Bokeh simulator and Diffraction.

Equipment and settings

Equipment: the camera and lens shown at the top of the screen set the sensor size, the circle of confusion, and the focal lengths and apertures offered. Tap them to change them.
The scene: a side view, with the camera on the left and infinity on the right, and the sharp zone drawn around the subject. Tap or drag the scene to set the focus distance.
Settings: set the focal length and the aperture with their slider or the − and + buttons, or tap the value to enter it exactly. Under the aperture slider, a coloured band shows the diffraction level of each aperture on this camera (see the Diffraction tab).
With a sensor smaller than full frame, the app also shows the effective focal and effective aperture (full-frame equivalents).
The focus distance can also be set at the bottom of the Settings card. The gear icon of this card changes the distance unit (mm, cm, m, km, in, ft, yd, mi).

The result

Just below the settings:

In front of subject and Behind subject: the part of the sharp zone on each side of the focus point, with its percentage. The sharp zone usually extends further behind the subject than in front of it.
Near focusing limit and Far focusing limit: the distances of the nearest and farthest sharp planes.
Depth of field: the total length of the sharp zone, or Infinity when it extends to the horizon.

Three rows then sum up the effects of the setting; tap one to open the matching tab:

Hyperfocal: the hyperfocal distance. When the focus is far from it, Focus here moves the focus there in one tap.
Bokeh simulator: the blur of a point of light at infinity, in image pixels.
Diffraction: the blur level caused by diffraction (Sharp, Very slight blur, Slight blur, Visible blur). This row only appears if the camera provides its pixel size.

Hyperfocal tab

The scene is redrawn with the focus on the hyperfocal distance: everything is sharp from half this distance to infinity. The card gives the hyperfocal distance, the circle of confusion used (CoC, in µm) and the maximum sharpness aperture (see the tips).

Inverse calculation tab

To find the aperture from the result you want:

Aperture for a given depth of field: the depth of field you want, at the focus distance set.
Aperture for a given hyperfocal distance: the hyperfocal distance you want.

Tap the value to enter it. The app gives the required aperture and the maximum sharpness aperture. If the calculated aperture does not exist on the lens, a ⚠ shows the available aperture range.

Bokeh simulator tab

Set the foreground and background distances; the scene places them around the subject. The app calculates the size of the blur discs of a point of light in the foreground, in the background and at infinity (∞), in mm (or inches) on the sensor and in image pixels. A night photo draws them to the scale of the image, around a sharp subject.

Diffraction tab

The more you stop down, the more light spreads as it passes through the aperture: a point becomes a small spot, the Airy disc. When this spot covers several pixels of the sensor, the image loses sharpness, even though the depth of field increases.

The drawing compares the light spot with the sensor pixels, with their size in µm and the number of pixels covered.
The aperture band colours each aperture by its level; the solid squares form the maximum sharpness range of this camera. A message tells you whether you are within this range, before it or beyond it.
Compare with f/… pins the current aperture: when you change the aperture, both spots are shown side by side.
At close focus (macro), the effective aperture is narrower than the aperture set. Set the lens pupillary ratio for an exact calculation; the tab then uses the effective aperture.
Details and explanations gives the exact values, the apertures from which the blur becomes slight then visible, and the sensor contrast curve by aperture.

If the selected camera does not provide its pixel size, the tab cannot do the calculation: choose a camera from the list or complete its details.

Understanding depth of field

Depth of field is the zone of the image in which objects look sharp: the distance between the nearest and the farthest sharp planes. Blur increases as you move away from the focus point, in front as well as behind.

The hyperfocal distance is the focus distance that gives the greatest depth of field up to infinity. Focusing at infinity, everything is sharp from the hyperfocal distance to infinity; focusing at the hyperfocal distance, everything is sharp from half this distance to infinity. For landscapes, it is therefore better to focus at the hyperfocal distance than at infinity.

Tips

Increasing depth of field

Move away from the subject.
Focus about a third of the way into the scene: the sharp zone extends further behind than in front.
Stop down (high f-number), without leaving the maximum sharpness range of the Diffraction tab.
Use a shorter focal length (wide angle).

Reducing depth of field

Move closer to the subject.
Open up the aperture (low f-number).
Use a longer focal length (telephoto).
Move the subject away from the background.

Portraits

For a medium or close-up portrait, focus on the nearest eye, with a sharp zone from the tip of the nose to the ears. A medium aperture, f/5.6 for example, gives this result while keeping the background blurred.

Aperture priority mode

The A or Av mode lets you choose the aperture, and therefore the depth of field. To avoid camera shake, combine it with auto ISO and a minimum shutter speed.

Maximum sharpness

For a given focal length and focus distance, the maximum sharpness aperture is the narrowest one that keeps roughly the same blur far in front of and far behind the subject. It makes the subject sharper without losing the background blur.

Example with a full-frame sensor, a subject at 2 m and a 50 mm lens: at f/3.5, the sharp zone goes from 1.85 m to 2.18 m (0.33 m). The tool gives f/8.7, i.e. f/9 on the lens: the sharp zone then goes from 1.65 m to 2.53 m (0.88 m), with a background that is still blurred.

Bokeh

The word bokeh comes from the Japanese boke (ボケ), “blur”. It refers to the aesthetic quality of the background blur. Its shape depends on the aperture blades: rounded blades give round discs, a hexagonal aperture gives hexagonal discs.

To get strong bokeh:

Use a fast lens (f/2.8 or wider) wide open, in aperture priority or manual mode.
Move closer to the subject and away from the background: the farther the background, the more blurred it is.
Look for points of light behind the subject: backlight, string lights, reflections.

The bokeh simulator shows the size of the discs before you shoot: compare several apertures and background distances.