Sponsored by

THE PRINCIPLES OF PHOTOGRAPHY:

Since the days of the Camera Obscura and its basic pinhole design, man has been fascinated with the idea that a moment in time can be captured and stored. The basic principle of the pinhole camera is implied in writings from before the birth of Christ, and it is certain that Leonardo Da Vinci was faliliar with basic camera design in the 14th century.

Even today with computers and technology on the rampage, the fundamental requirements for taking photographs remains unchanged. All cameras, and that includes digital, conventional film, APS, and video, require 3 key elements. A light-proof box, a means of focusing the image, and a medium with which to capture that image. In that respect, the whole field of photography has remained unchanged for many thousands of years. What has changed of course is the way these three basic components are built, and how they interact with each other. Over time, extra features have also been added to help control the ammount of light that enters the camera, and the sensitivity and quality of the medium used to perform that final capture. Just as photographic film has improved in leaps and bounds over the decades, so the same is true of the Charge Coupled Device (or CCD) the digital camera's equivelant of photographic film, only the CCD has had to mature in a much shorter timespan. We will look at the CCD in more detail later on.

OK, so we've seen that we need a light-proof box (the camera), a means of focusing the image (the lens) and a medium with which to capture that image (the CCD). How then do we control the ammount of light that actually enters the camera? You may have seen old films where a photographer would remove his lens cap, count to a certain number, then replace it again. This worked just fine with old plate film which had extrememly low light sensitivity, but with modern cameras needing bursts of light with a duration of hondredths or even thousandths of a second, that method quickly stopped becoming a viable option. The answer for the modern camera lies in the use of high precision electronic shutters. These shutters can open and close in as little as 1/8000th of a second on high spec. pro SLR (Single Lens Reflex) cameras, and can remain open for as long as required when shooting in low light (known as a BULB setting). Perhaps not surprisingly, the ammount of time for which the shutter remains open is known as the SHUTTER SPEED

But the shutter is not the only way to control the ammount of light entering the camera, there is also the APERTURE. The aperture is basicaly a hole that sits amongst or behind the glass elements that make up the lens, and is variable in size to alter the ammount of light entering the camera. For less light you use a small aperture, for more light you use a large aperture. These apertures are measured using what's known as F stops. A large aperture (which lets in the most light) will have a low F stop number such as F1.8, whereas a small aperture (which lets in less light) will have a high F stop value such as F16. If the idea of a high F stop value letting in less light and a low F stop value letting in more light seems a little confusing, do what I did in the early days and think of these numbers as the ammount of light being blocked rather than the ammount being allowed through.

I should imagine many of you are now asking yourselves why you need two methods for controling how much light enters the camera. Why not use just the shutter? Let's move on and have a look why.

Page 3- Apertures and shutter speeds