Tuesday, February 10, 2009

An exposure to ‘exposure settings’

I was discussing with one of my friends regarding exposure settings of a digital Camera, mostly DSLR or DSLR like cameras. In this article I would try to explain concepts of Aperture (F-Stop or F Number), Shutter Speed, ISO, Exposure Compensation, P, A, S and M modes.


Capturing a good picture is all about good lighting. Its not what light “you” see, its the light what camera sees. All the entities listed above are one way or the other linked with light that Camera sees. We call it as “Exposure”. A well lit picture is called well exposed picture, poor lighting makes it under-exposed.

Let us now try to see how all the above factors affect the exposure of a picture.


Aperture is the width of the lens opening, when you release the shutter. Larger the aperture, more the light goes inside the camera. Apertures are measured in F-Stops or F-Numbers (F/4 or F/5.6 and so on). Smaller the F-Number, larger the aperture. So, if you set aperture to be F/2.8 a lot of light is allowed inside. If you set it at F/22, very small amount of light is let in, when shutter is released.  Learn more about about aperture here

Impacts of Aperture:

  1. Aperture impacts the DOF (Depth of Field) of the picture. Higher the aperture (Small F-number) Shallower the DOF. Read more about it here

Shutter Speed:

Shutter speed determines how long the shutter is opened, when you release it. Higher the shutter exposure (measured in seconds), longer the shutter is opened and hence more light is allowed inside the camera. Example: As daylight is well lit, and hence shutter speed can be as high as 1/1000s, 1/2000s . Of course, this goes in conjunction with other exposure parameters likes Aperture, ISO etc. In poor light – Night shots, indoor shots, you might have to lower to 1/10 or even it can several seconds. But you should keep in mind the picture can be shaken as we go for long exposure.

Learn more about shutter speed here

Impacts of Shutter Speed:

  1. Scene can be frozen with very short exposure. This can be used for moving objects. Example – Deepavali
  2. We can get some dramatic effects of water falls or other moving objects with moderately long exposure. Example – Waterfalls, Bubbleman
  3. Long exposure can cause shaky pictures. Tripod or Image Stabilized Lenses can reduce this problem. Example– Deepavali Group
  4. Long exposure when not needed can also cause over exposed pictures Example – Flower Pot


ISO (Sensitivity):

ISO represents the sensitivity of the sensor. The concept of ISO was originated from film cameras. Each film would be having defined sensitivity measured in ISO equivalent number. In digital cameras the sensitivity is controlled digitally, which are equivalent to that of film roles. ISO Rating 100 being very low sensitivity and 3200, which is highly sensitive to the light. Thumb rule is, better lit place use less ISO and poor lit place (night, indoors) use higher ISO rating.

Learn more about ISO here

Impacts of ISO:

  1. Higher the ISO, camera becomes very sensitive and starts recording unwanted light particles called Noise. Example Writing with experience
  2. Moderately high ISO helps to get better exposure in bad lighting
  3. Better to use lower ISO in well lit conditions. Example Day light

Mode of Shooting (P,A,M,S):

After understanding basics of above exposure parameters, let us try to understand how to use different modes. Which one to choose when. Before going further, we need to understand that camera exposes the light into the sensor based on all the settings mentioned above. So the net result depends on the current settings of the camera. The objective is to control these parameter effectively to get good picture.

NOTE: It is very difficult to manage all these parameter ourselves (M Mode). So most of the manufactures have given facility to fix few of the parameter and leave rest to the camera, so that it determines what should be the correct value of other parameters in that respective lighting condition.

Mode A  (Aperture priority Mode) : In this mode you can capture a picture with fixed aperture. Camera will determine the appropriate shutter speed for that lighting condition and ISO setting. This is very useful when you want a specific DOF OR when you need a bokeh (Background blurr), you might want to use a specific wide aperture.

Mode S (Shutter Priority Mode): In this mode you can fix the shutter speed and let camera calculate the correct aperture for the current lighting conditions and ISO. This is useful when you know what should be the shutter speed. For example, you like to take a picture with long exposure say 8 Seconds, Night shot. Example Nighty Road. Another example would be, if you want to have some movement effect in your frame, instead of freezing. Example Kick the ball

Mode P (Programmable Auto Mode): This is favorite mode of many photographers. This would give blend of both A and S. You can change either S or A and other parameter is calculated automatically.

Mode M (Manual Mode): In this mode, camera switches its brain off. It is completely in your control. You can set Aperture, Shutter Speed, ISO, White Balance and what not. This is not so easy unless you know what happens when you select a particular value. This is also an excellent way you learn about exposure settings. Takes loads of photos in M Mode and understand how you Camera Sees a frame.

Exposure Compensation:

With any of these above settings you can use exposure compensations which usually ranges from – n EV to +n EV. In my camera it is –5EV to +5EV. Suppose you do your settings at 0EV and capture a scene and found that it was under exposed. Now to improve the capture you can either change one of Aperture, Shutter or ISO  OR you can simply change Exposure Compensation to +1EV. Camera automatically changes what ever it needs to get better exposed image. In reverse if the scene was washed out (Over exposed), you can make it –1EV to reduce the exposure.


Hope this helps…. Please provide your sincere feedback


ಸುಶ್ರುತ ದೊಡ್ಡೇರಿ said...

Thank you very much for this lesson! This is very helpful for me.

ShILpZ... said...

hey suni...thx 4 dz wonderful blog!! :) really helpful!!

Sri said...

Obvious that you've made a lot of effort and passion while writing this post. Great!

Vinodkumar said...

Karthik..plz upadate all your knowledge about the photography..its helpful for beginners like me.......Thanks for your effort....

workhard said...

HI.. thats a good post.. very informative..