The summer months are approaching and with them comes nice weather and vacations. Each year the number of photos taken at any given moment grows exponentially as integration into more devices makes it easier and easier for people to take photos. Knowing how to use your camera and keeping a few things in mind can go a long way in improving your resultant photos. I will be writing an article each issue this term discussing ways in which you can improve your general purpose photography.
In this issue I will go over the typical “Photography 101” topics, which lay the foundation for further topics. We will begin by defining exposure.
The concept of exposure can be simplified to be the brightness of an image. The camera will change various settings such as aperture, shutter speed and sensitivity in order to control the amount of light that forms the resultant photo. Changing each of aperture, shutter speed and sensitivity (ISO) will have different effects on the photo and must be kept in mind depending on the situation.
Aperture:
Aperture is the size of the opening that allows the light to enter the camera. Camera lenses contain blades, which can be closed to form a variable sized hole through which the light passes. A larger hole means more light and a smaller hole means less light. The size of the hole can be described using an f-number, which is defined as the ratio of the focal length of the lens to the size of the opening. Therefore a larger opening would be described using a smaller f-number such as f1.4 or f2.8 and a smaller hole would be described using a larger f-number such as f8 or f11. The consequence to adjusting the size of the aperture is not only a change in the amount of light but also the Depth of field of an image. The wider aperture will allow the maximum amount of light onto the sensor but also creates a very shallow depth of field, which means that the object on the focal plane will be well focused but almost everything else will be blurry. If you have a smaller aperture (bigger f-number) less light will be able to reach the sensor but the depth of field will be very deep. Therefore when in a dark situation you want to try and use the smallest possible f-number so that your opening is large, however you must be careful since focusing becomes trickier.
Shutter Speed:
Shutter speed is the amount of time which the shutter is open, exposing the sensor to the light. Most cameras (some of the smaller digital ones do not) have a door covering the sensor or film so that they are not exposed to the light at all times. When the shutter button is pressed on a camera, the door opens for a short period of time, exposing the sensor or film to the light which is analogous with taking a picture. The amount of time for which the door is open controls the amount of light that can be collected. You can think of it similar to a bucket in the rain, if you put a bucket outside in the rain overnight, you will collect more rain then if you put it outside for a few minutes. In many situations we want to collect as much light as possible and it would therefore make sense to leave the shutter open for longer. The downside of this, is that while the shutter is open it is capturing the contents of the scene which may or may not be stationary. The slower your shutter speed the more opportunity the objects in the scene, or the camera have to move and this will result in blurry photos. Therefore it is important to choose a shutter speed that is fast enough to capture the motion of the scene but also slow enough to allow enough light in. This is a good thing to keep in mind when taking photos of fast moving objects such as sports but this will be discussed in further articles.
Sensitivity (ISO):
The ISO or sensitivity of the capturing medium is a measure of how sensitive the film or sensor is to the light. In film terms, it was the sensitivity of the chemicals to the light, but in digital terms it is the gain applied to the received signal. The drawback to having a higher ISO is that with gain comes noise and therefore as ISO is increased, random coloured specs called noise begin to appear in your image. ISO or ASA is the standardized measurement of the sensitivity of film but has been adapted to the digital domain and most manufacturers do their best to match the sensors sensitivity with the measurement, although results can be variable. The base ISO is typically 100 with the standardized values doubling at every level with most modern cameras reaching values of up to 6,400iso.
Putting all of these concepts together allows the camera to produce an image, which has the proper brightness level. There are many different combinations of the three variables, which produce the same brightness level. The camera is organized so that changing one of the three variables will double the light or reduce it by a half and is referred to as a stop. For example, if you needed to increase the shutter speed but still get the same exposure you would either have to increase the ISO or go to the next f-stop. Shutter Speed of 1/100, Aperture of f4.0 and ISO 200 would be the same brightness as the settings 1/50, aperture f2.8 and ISO 200 or 1/50,f4 and ISO400.
It’s a difficult concept to explain in an article, so the best way to understand these concepts is to try it. DSLRs make it very easy to change these settings but you can usually still do it on a point and shoot if you can locate them within the menus.
This article lays the foundation for future articles and I will be mentioning these concepts often. Hopefully you learned something about how your camera works and are looking forward to my future articles!
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