Many photographers think that understanding Exposure is the toughest aspect in photography. Several people may shy away from a DSLR because they have to understand some of the alien terms like Aperture, Shutter Speed, ISO, etc.
The reality is that understanding these key concepts is easy and fun.
It requires a bit more time and patience to understand it in depth. Aperture, Shutter Speed and ISO are the basic building blocks of photography. If you understand how each of them work together to get an optimal exposure, you will enjoy your photography to the fullest.
To make the camera see the way we see is the most difficult aspect in photography. But, as we understand more about the exposure, we will be able to make the camera see what we want it to see.
I will write series of articles about the core concepts of Exposure called Aperture, Shutter Speed and ISO to make it easy to understand.
We all know that we see the world through our eyes with the help of light. When there is absolutely no light, then we do not see anything. In a way, our eyes are exposed to light to form a picture in our brain through which we perceive/understand our world.
A photograph is made when the lens (or eyes) bends the light onto the sensor (or brain) to form a photograph (or picture).
Exposure, in simple terms, means how much time the camera sensor is exposed to the light to make a photograph.
The amount of light passing through the lens opening (Aperture) for a specified duration of time (Shutter Speed) for which the camera sensor is open is called the Exposure.
Exposure is essentially a combination of Aperture, Shutter Speed, and ISO. To keep the matters simple, let us concentrate only on Aperture and Shutter Speed and keep the ISO for later articles.
Here is a simple equation for exposure:
Exposure = Aperture + Shutter Speed + ISO
A properly exposed photograph will contain proper color information and all the details that are present in the actual scene.
A photographer’s life is so much easier in today’s digital world due to histograms. You can see if the exposure is correct or not by looking at the histograms. However, the knowledge of exposure will enable you to achieve optimum exposures to fulfill the artistic needs and to achieve creative results.
If the amount of light passing through the lens opening for a duration of time when the camera sensor is open is less than optimal, then it is called underexposure.
The underexposed photograph will look darker than the real scene.
Underexposed photographs usually lack details in the shadow regions resulting in the crushed blacks. The histogram of such photographs, show the distribution towards the left most side with some clipped blacks.
If the amount of light passing through the lens opening for a duration of time when the camera sensor is open is more than optimal, then it is called overexposure.
The overexposed photograph will look brighter than the real scene.
Overexposed photographs usually lack details in the highlight regions resulting in the washed out details. The histogram of such photographs, show the distribution towards the right most side with some clipped whites.
If the photograph looks closer to reality, then the exposure is optimal. As photographers we may decide to either expose and develop the photograph to depict the reality or to depict our artistic vision.
Exposure Range or Dynamic Range
Every camera possesses an exposure range or dynamic range that depicts its capability to collect the light information. This light information is later converted to a suitable form to represent a photograph.
In simple terms, an exposure or dynamic range is nothing but the lowest and the highest exposure a camera can record in a given scene. Or the darkest and the brightest details a camera can record in a given scene.
Dynamic range may vary from camera to camera based on how much light the sensor can hold. The larger the sensor and its pixel size, greater the dynamic range, since it can capture higher amount of light.
For example, consider a camera that has 5-stops dynamic range. Suppose, the main subject needs an aperture of f/11 (with constant shutter speed of 1/125th of a second), then everything in the scene that requires an aperture of f/5.6 to f/22 will be represented properly.
Anything below f/5.6 will result in pure black and anything above f/22 will result in pure white.
Note: The Shutter Speed and ISO are assumed to be constant
Let us understand the dynamic range using Shutter Speed instead. Suppose, the main subject needs a shutter speed of 1/125th of a second (with constant aperture say f/11), then everything in the scene that requires a shutter speed of 1/30th to 1/500th of a second will be represented properly.
Anything below 1/30th of a second will result in pure black and anything above 1/500th of a second will result in pure white.
Note: The Aperture and ISO are assumed to be constant
I have considered a 2-stop lower and 2-stop higher than the normal for the sake of explanation. In reality, the film cameras (or negatives) usually tend to preserve more details in the brighter regions than the darker regions. The digital cameras tend to preserve more details in the darker regions than the brighter regions.
In Part-II, we discuss about Acheiving Optimal Exposure for various scenes like Low-key, High-key, HDR, and Normal scenes.