LESSON 53
Depth of field and hyperfocal distance
How much is sharp, and where to focus.
IN THIS LESSON
- What depth of field is
- The four levers
- Hyperfocal distance
- In practice: using it in the field
What depth of field is
Depth of field is the distance between the nearest and the farthest things that look acceptably sharp in a picture. A lens focuses at one distance only, so acceptable has to be defined. It is defined by the circle of confusion: the largest blur spot that still looks like a point. For full-frame cameras a common limit is the frame diagonal divided by 1500, about 0.029 mm, and values of 0.030 and 0.033 mm are also used. That figure corresponds to a print of about 30 cm diagonal. View larger, or closer, and less of the picture will look sharp.
The four levers
Four things set depth of field: aperture, focal length, distance and the circle of confusion. The source gives an approximation in which depth of field grows with the f-number and the circle of confusion, grows with the square of the subject distance, and shrinks with the square of the focal length. So stopping down from f/4 to f/8 roughly doubles it, while stepping back to twice the distance roughly quadruples it. Very close subjects get very little depth, which is why macro work fights for every millimetre. Lesson 01 explains aperture itself.
Hyperfocal distance
The hyperfocal distance is the closest point you can focus on while keeping infinity acceptably sharp. Focus there and everything from half that distance to infinity looks sharp. That makes it the most useful setting for landscapes and street work at small apertures, and the ideal setting for fixed-focus cameras. Thomas Sutton and George Dawson wrote about it in 1867. The formula is the focal length squared, divided by the f-number times the circle of confusion, plus the focal length. The table uses 0.029 mm and shows how quickly the distance grows with longer lenses. The figures are computed here from that formula.
In practice: using it in the field
This section is working practice. Exact hyperfocal focusing leaves the far distance only just acceptable, so many landscape photographers focus a little beyond the hyperfocal point to keep the horizon crisper, giving up a little foreground sharpness. Do not stop down too far to gain depth: beyond about f/11 on many cameras, diffraction softens everything. If you need more depth than one frame gives, use focus stacking, which lesson 56 explains. Check sharpness on the screen at full magnification, at both the nearest and the farthest important detail, before you leave the spot.
| Focal length (full frame) | Hyperfocal at f/8 | Hyperfocal at f/11 |
|---|---|---|
| 16 mm | 1.1 m (sharp from 0.6 m) | 0.8 m (sharp from 0.4 m) |
| 24 mm | 2.5 m (sharp from 1.3 m) | 1.8 m (sharp from 0.9 m) |
| 35 mm | 5.3 m (sharp from 2.7 m) | 3.9 m (sharp from 1.9 m) |
| 50 mm | 10.8 m (sharp from 5.4 m) | 7.9 m (sharp from 3.9 m) |
Try it today
- 01Set a 24 mm view and f/8, and look up your camera's distance scale or use a phone app.
- 02Focus at about 2.5 m and check that a near rock and the horizon both look sharp.
- 03Now focus on the horizon instead and see where the near sharpness ends.
- 04Make the same frame at f/16 and compare overall sharpness at full magnification.
- 05Write the hyperfocal distances for your favourite lens on a card in your bag.