Aperture and depth of field

Aperture and Depth of field in Photography

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.

Representation of Depth of field in black and white FRONT(plane A) MID(plane B) REAR(plane C) front middle rear side view LENS f/1.4 f/5.6 f/22 Depth of Field at aperture

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 :

... f/1 ... f/4 ...portrait, astro, low-lightminimum or shallow or narrow depth of field
... f/4 ... f/8 ...street, documentary, journalismmedium depth of field
... f/8 ... f/13 ...landscape, cityscape, architecturesmore depth of field than above
... f/13 ... f/22 ...landscape, macromaximum 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:

◉ Aperture
◉ Lens-to-subject distance
◉ Focal length

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.

Depth of field with different apertures Depth-of-field at large aperture Depth-of-field at medium aperture Depth-of-field at small aperture Effects of different apertures on DEPTH OF FIELD

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.

shallow depth-of-field with large aperture

Exif: f/1.8, 1/200 sec., ISO-800, 52mm eqv.,
Nikon d7000, Nikkor 35mm f/1.8, Puri, Odissa, India 2014.

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.

deep depth-of-field with small aperture

Exif: f/6.3, 1/40 sec., ISO-5000, 52mm eqv.,
Nikon d7000, Nikkor 35mm f/1.8, Puri, Odissa, India 2014.

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.

shallow depth-of-field with large aperture blurs background

Exif: f/1.8, 1/30 sec., ISO-250, 52mm eqv.,
Nikon d7000, 35mm f/1.8(DX), Badarpur, Karimganj, India 2014.

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.

deep depth-of-field for landscape with small aperture

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.


An image recorded through different aperture values f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22 Different apertures at 70mm, iso 64

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.

Flower at aperture f/2.8 shallow depth-of-field creamy bokeh

Exif: f/2.8, 1/640 sec., ISO-100, 85mm eqv.,
Nikon d810, Nikkor 85mm f/1.8, Badarpur, Karimganj, India 2017.

butterfly flower at aperture f/3.5 depth-of-field shallow

Exif: f/3.5, 1/500 sec., ISO-80, 70mm eqv.,
Nikon d810, Tamron 24-70mm f/2.8, Mumbai, Maharashtra, India 2016.

Large apertures are suitable for portraits, lowlight, astro, flowers, butterflies.

street candid at aperture f/5 depth-of-field medium

Exif: f/5, 1/25 sec., ISO-4000, 24mm eqv.,
Nikon d810, Tamron 24-70mm f/2.8, Benaras, UP, India 2015.

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.

landscape at aperture f7 depth of field large

Exif: f/7.1, 1/30 sec., ISO-320, 27mm eqv.,
Fuji X-T30, Fuji 18-55mm f/2.8-f/4, Badarpur, Karimganj, India 2019.

Small apertures are suitable for landscapes.

spider macro at aperture f/25 depth-of-field largest

Exif: f/25, 1/500 sec., ISO-6400, 140mm eqv.,
Nikon d810, Nikon 70-300mm, Panchgram, Hailakandi, India 2016.

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.

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