parallel effect of changing apertures. It’s called depth of field

Playing Tricks with Light

Our next installment of photography lessons. Now that we’re getting into the finer details of digital photography, here are two new lessons to learn and try out!

We talked about exposure control in our last issue, and the three vital tools that control it: Aperture, Shutter Speed and ISO. Setting the right exposure is all about playing with either one or all of the three control tools in combination. Now, we have two new things to understand and try out with the help of our previous lessons.


You must have noticed in many images, the background goes out of focus thus making the subject look relatively much more prominent, focused and sharp (Fig 1). This effect is usually not seen in images shot with a point and shoot camera, unless used in macro mode for close-up shots of small objects. How does it happen with a digital SLR then? The credit goes not to the camera but to the lens.

Playing Tricks with Light

Photo: Dr Caesar Sengupta

The primary function of aperture is to control light that passes through the lens. The standard f numbers, which are nothing but units of the size of the aperture are expressed as f1.4, f2.8, f4, f5.6, f8, f11, f16, f22; lower the f-stop, wider the aperture and vice versa. In other words, f/1.4 is a very wide aperture and allows a lot of light to pass through while f/22 is a narrow aperture and wouldn’t allow much light to pass through. But there is something very interesting which comes along as a parallel effect of changing apertures. It’s called depth of field. Look at the image (Cover Photo). You can observe that there is only a thin strip along which you can appreciate the sharpness of the subject. Anything in front and anything behind that strip is out of focus. This is a much desired effect in photography, which helps the photographer to keep various elements in the frame within or out of focus.

In this issue, we will focus only on the application of aperture in controlling this depth. Depth of field is the range of distance within the subject which is acceptably sharp. It is controlled by three factors:

  1. Aperture – The wider the aperture, the shallower is the depth of field (Fig 3)
  2. Focal length – The longer the focal length, shallower the depth of field
  3. Focal distance – The nearer the subject, the shallower is the depth of field
Playing Tricks with Light

Photo: Saritha Dattatreya

For example, a wide aperture may help you get a good portrait photograph since it causes a blurred out background. Similarly, a narrow aperture may be very useful for landscapes since you would want everything from foreground to background up to infinity to be in focus.

Exercise 1

Keep a note of the table in the next page as a quick reference. Find a subject first – could be your sister or grandpa, or maybe your dog or a nice landscape to shoot. Rotate the mode dial in your camera to A (or Av), also called the aperture priority mode and change aperture as per the need indicated in the table. Apertures like f/2.8, f/4, f/5.6 etc are wide apertures and apertures like f/11, f/16 or f/22 are narrow apertures.

Situation – What to use

Portrait Aperture – wide

Wildlife Aperture – wide

Landscape Aperture – narrow

Here are a few examples for you to try (Fig. 4, 5 and 6)

Playing Tricks with Light

Photo: Dr Tanmoy Das


Playing Tricks with Light

Photo: Dr Caesar Sengupta


Playing Tricks with Light

Photo: Saritha Dattatreya


You are aware that the primary function of the shutter speed is to control light. It is expressed as fraction of seconds, such as 1/4 second, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, etc. Higher (faster) the speed – lesser is the exposure. But the parallel effect that it brings along, is freezing of movement when shutter speed is fast and imparting a motion blur when shutter speed is slow.

Exercise 2

Find a subject first – either a falling stream of water from a tap or your friend cycling or skateboarding fast or go out in the street during evening when the street lights are on. Rotate the dial in your camera to S (or Tv), also called the shutter priority mode, and change shutter speed as indicated in the table.

Here are a few ideas for you to try:

(Fig. 7 and 8)

Situation – What to use

Sports / Action Shutter – fast

Night / Low-light Shutter – slow

Playing Tricks with Light

Photo credit: Dr Caesar Sengupta


Article Originally Published in October 2014 Issue of Saevus Magazine

Cover Photo by Pratik Chorge

Read also:  Of Dancing flames and Geese

Have an interesting article you’d like to share with us? Send articles at and get a chance to be featured on our blog site! So what are you waiting for? Hurry!

Have something to add to this story? Tell us in the comments section below.


About the Author /

A dedicated wildlife conservation photographer, Caesar is Founder of Dr Caesar Photography, Founder of DCP Expeditions LLP, also a freelance writer, trainer and National Geographic award winner. He is an MD, Medical Microbiologist by profession, who conducts regular wildlife photography workshops and field expeditions across the country and abroad.

Post a Comment