What
lens...
I. The Basics
by J. Ramón Palacios
tell
a friend about this article
|
FOCAL
LENGTH, F-STOP AND DEPTH OF FIELD
Depth
of field (DOF) is the
distance between the farthest and nearest points which are
in
focus. This can also be identified as the zone of acceptable
sharpness in front of and behind the subject which the lens
is focused on. DOF varies according to several
factors such as lens focal length, aperture, shooting distance,
etc.
|
| 50mm
f/1.4D AF Nikkor |
DOF
is inversely proportional to focal length,
i.e. the shorter the focal length (f), the larger
the DOF. So, in general terms, wideangle lenses -a
28mm for example- have larger depth of field than
telephoto lenses -a 105mm for example- which are
therefore said to have a shallow depth of field.
So, if you want a shallow DOF in a portrait, it is
best to use a telephoto lens.
DOF
is directly proportional to the f-stop number,
i.e. the smaller the aperture (bigger f-stop number),
the larger the DOF. Images taken at f/11 will have
more depth of field than those made at f/4, for
example. Therefore, if you want a shallow DOF in
a portrait,
it is best to use a telephoto lens at a wide (small)
aperture, like in the splendid candid by Nikonian Luc Van
Nieuwenhove (LucVN) and show at right. |
|
 |
Below
a table with sample values to illustrate the two points above.
|
Lens
focused at
20 ft / 6.1m |
f/stop |
Near
focus limit |
Far
focus limit |
DOF |
| 24mm |
f/8 |
6.43ft
/ 1.96m |
Infinity |
Infinite |
| |
f/2.8 |
11.5ft
/ 3.5m |
78.6ft
/ 23.9m |
67.1ft
/ 20.5m |
|
50mm |
f/8 |
10.1ft
/ 3.1m |
1,989ft
/ 606.3m |
1978.9ft
/ 603.2m |
|
|
f/4 |
16.1ft
/ 4.6m |
26.4ft
/ 8.05m |
10.3ft
/ 3.1m |
| 135mm |
f/8 |
18.8ft
/ 5.7m |
21.4ft
/ 6.5m |
2.6ft
/ 0.8m |
|
f/4 |
19.4ft
/ 5.9m |
20.7ft
/ 6.3m |
1.3ft
/ 0.4m |
|
200mm |
f/8 |
19.4ft
/ 5.9m |
20.7ft
/ 6.3m |
1.3ft
/ 0.4m |
|
|
f/4 |
19.7ft
/ 6.0m |
20.4ft
/ 6.2m |
0.7ft
/ 0.2m |
| 300mm |
f/8 |
19.7ft
/ 6.00m |
20.4ft
/ 6.22m |
0.7ft
/ 0.21m |
|
f/2.8 |
19.9ft
/ 6.07m |
20.1ft
/ 6.13m |
0.2ft
/ 0.06m |
You can find at the following link a practical
illustration for understanding
Depth of Field, Aperture & Shutter Speed Relationships
DEPTH OF FIELD AND HYPERFOCAL DISTANCE
In
simple terms, the hyperfocal distance is the intrinsic characteristic
distance of a lens where DOF is maximized when the lens is
focused at it; then the near focus limit will be half the
hyperfocal
distance
and the far focus limit will be infinity. For more on the subject
see: DOF
& Hyperfocal Distance, samples, tables, calculator
and formulas.
. |
