Depth of field, in photography, is the sharp area in front of
and behind the subject on which the lens is focused.
Note:
By the term "subject on which the lens is focused"
we mean the area/zone/plane which we want to be the sharpest.
Any photograph has some sharp area
(we call this area in focus)
and some unsharp or blurred area
(we call this area out-of-focus).
We can imagine that the area/field in front of our camera is made up of
infinite number of planes, three of those planes (A, B, C) have been
shown in the following animation.
All those planes will not have the same sharpness.
In the above, white colour represents the depth of field
(area in-focus, or the
sharpest area of the zone).
Black colour represents the
area out-of-focus, or the blurred area of the zone
The above settings are an approximate
representation of the behaviour of depth of field at different
apertures.
Assume that the focus-point is constant on the small green boxes;
and the focal-length to be around or above 85mm.
For the above graphical representation, three apertures settings
f/1.4 (very large aperture),
f/5.6 (medium aperture) and
f/22 (very small aperture)
are being applied one by one.
Plane A is the nearest area of the lens,
while plane C is the farthest. A side-view of the field is displayed on the bottom
of the animation.
At large apertures like f/1.4, we find only
a small portion of the field to be in focus or has acceptable sharpness
(the white portion). Rest of the field (major black portion) is out-of-focus.
But, at a very small aperture like f/22, we get a very large depth-of-field,
from plane A to plane C almost.
What we learn is: larger the aperture-diameter, thinner or smaller
the depth of field; and smaller the aperture-diameter, deeper or larger
the depth of field.
Note: A shallow or small or thin
depth of field captures a very small area
in focus. A very small portion of the scenario will be sharp,
major portion will remain out-of-focus. On the other hand,
a deep or large depth of field captures a large portion of the scenario
in focus, i.e., major portion of the scenario will have acceptable sharpness.
Different ranges of apertures are used for different genre
of photography to achieve the intended depth of field.
The following list may be of some guidance in this respect :
APERTURE RANGE
WHEN TO USE
DEPTH-OF-FIELD
... f/1 ... f/4 ...
portrait, astro, low-light
minimum or shallow or narrow depth of field
... f/4 ... f/8 ...
street, documentary, journalism
medium depth of field
... f/8 ... f/13 ...
landscape, cityscape, architectures
more depth of field than above
... f/13 ... f/22 ...
landscape, macro
maximum or deep depth of field
The above settings are not to be followed rigidly.
They only tell about different depths of field required for
different genre of photography. We are not bound to shoot
portraits within f/4; apertures as small as below f/8 can be
used to do that depending upon the other variables like focal length,
lens-to-subject distance etc.
On the other hand, I won't hesitate to shoot a landscape
with a large aperture(with compromised depth of field for landscape)
when it is absolutely necessary.
Note: Throughout the explanation of depth-of-field in this
page, the terms like small, shallow, narrow, thin and minimum
do have the same meaning (less depth-of-field). Whereas the words like large,
deep, wide, thick and maximum mean the same (more depth-of-field).
This is hold true w.r.t. the term depth-of-field.
In general, the following three factors are responsible for
the depth of field in a photograph:
In the
previous page
we have seen how aperture effects the exposure of a photograph.
Now let us see how it effects depth of field of the same.
The remaining two factors, which effect the
depth of field in photography, will be found in
this page.
Effect of aperture on depth of field
When we use a large aperture to shoot, we get a shallow or
small depth of field; and a small/narrow aperture results
in a large depth of field.
For portrait works, in
general, we want our subject to be sharp, and everything else
to be blurred out. So, a very shallow/thin depth of field is
required, which is achieved by applying a large/wide aperture
like f/1.8, f/2 etc.
On the other hand, when we use a narrow aperture to shoot,
we get a very deep or large depth of field. For landscape or cityscape
works, we want the whole scenario in front of
the lens to be sharp (in focus), which is achieved by applying a
narrow aperture aperture like f/8, f/9, f/10 etc.
In case of macro photography, the subject acquires so much
magnification,
that sometimes even using apertures like f/22 falls short
for the required depth of field.
This happens because of the very short distance between the lens and the subject.
It simply means that
for macro photography, we require a very large depth of field,
for which sometimes focus stacking may be required.
Large aperture → Thin DOF,
Small aperture → Large DOF
Thin DOF → Small area/zone in focus,
Large DOF → Large area/zone in focus.
Note: The above image is nothing but a replica of the previous
black and white animation where effects of different
apertures on depth of field are shown.
The above image has a very shallow depth-of-field.
A large aperture of f/1.8 was used to get the intended effect.
The sharpest zone is the large yellow mask where focus-point was
placed. The focal length of 52mm eqv. also contributed to the
depth-of-field achieved.
But I did not intend to shoot the above image like the previous
one. I decided to bring all the bottles in
focus, and applied a small aperture of f/6.3.
I had to adjust the shutter-speed and ISO accordingly before pressing
the shutter-button to properly expose the scenario. As a result,
all the bottles achieved minimum sharpness.
The above is one of my favourite photographs taken in my quarters' garden.
This common lime butterfly allowed me to be as close to it as possible
and did not fly away. Since the
minimum focus distance of this
prime lens
is 1 feet, I assume that I took the shot from 1 feet distance. This allowed
maximum magnification and shallowest depth of field and blurred out almost
anything except the butterfly.
Exif: f/11, 1/40 sec., ISO-125, 16mm eqv.,
Nikon d810, Nikkor 16-35 f/4, Srinagar, Jammu and Kashmir, India 2018.
But, in the above image, proper foreground, mid-ground and background are
present. So, I applied an aperture of f/11 to obtain deep or large
depth of field, so that all the elements remain in focus.
animation
Different shutter-speeds were used to keep
the exposure constant. Since those images
were shot outdoors, some difference in
overall exposure may be found.
From the above animation, we find that
◉ Large apertures produce shallow/narrow/minimum depth-of-field.
◉ Small apertures produce deep/wide/maximum depth-of-field.
In the above animation, a group of seven images are displayed
one by one. The images have different apertures, from large to
small. The depth-of-field in the images varied, as per variations of apertures.
Note: In spite of variations of apertures, the overall exposure/brightness
remained same in all the images, because I used different shutter-speeds
along with different apertures.
Medium aperture: suitable for street photography in such lowlight. Note: The above is a sudden candid shot. The unintentional
slow shutter-speed used here could have ruined the photo.
Very small apertures are suitable for macro photography.
Note: Despite using a very small aperture, we get a shallow DOF
because of the high magnification in the above image.
This magnification is the combined result of very short lens
to subject distance, and the long focal length.
Be aware of this range of apertures, like f/25 ..., because
diffraction can cause loss of sharpness.
