The word Photograpghy is a derivation of two Greek words, “photos” which means light, and “graphos”, which means write. So, to photograph, means actually “writing with light”.
The principle of the camera had been known for quite some time, when the first permanent image was made. In reality, it is merely technical improvements that differentiate the first cameras, the “camera obscura”, from the ones we use today. The first versions of the Aperture, has been described in ancient times. Aristotle and Euclid described a pinhole camera, a simple camera without a lens with a single aperture – a lightproof box with a hole in one side, in the 5th and 4th centuries BC. Aristotle (384 – 322 BC) found that the light projected round spots of light even though the pinhole was square.
After Joseph Nicèphore Nièpce created the first permanent image in 1826, photographing has been under constant development. In 1888 the first Kodak camera was introduced, with a roll of paper, which changed to a roll of film the next year. In 1907 the first commercial colour film was manufactured. In 1914, Oscar Barnak develops a camera using the modern 24x36mm frame and sprocketed 35mm movie film. In 1936, we saw the development of Kodachrome, the first multi-layer colour film, and also the development of Exakta, a 35mm single-lens reflex (SLR) camera. In 1949 Carl Zeiss develops the first SLR with an unreversed image in a pentaprism viewfinder. The Nikon F was introduced in 1959, and in 1963 the first colour instant film was developed by Polaroid. In 1985 Minolta presents the world’s first autofocus SLR system – the “Maxxum”. In 1987 came the Canon EOS system. The first digital SLR was a modified Nikon F3 presented by Kodak.
Aperture, or f-number (f-stop)
Inside the lens you find diaphragm opening. This is what we refer to as the Aperture. The size of the diaphragm opening regulates the amount of light passes through onto the sensor (or film) inside the camera when the shutter is activated.
Back then, the photographer had to calculate the correct aperture using mathematical formulas. Then a plate with the correct aperture was inserted in a gap in the objective. We do not measure the size of the aperture today either – we use so called f-numbers, or f-stops. Today when we specify an aperture of a lens, this is the maximum aperture. Sometimes this is a fixed number (for all primes, and some zoom-lenses), but it usually changes with the focal length. For the prime Sigma AF 50mm f/1.4 EX DG HSM, the aperture is f/1.4. For the zoom lens Sigma AF 17-70mm f/2.8-4 DC HSM OS the aperture is f/2.8 at 17mm focal length, and changes to f/4 at 70mm. The f-number does not specify a fixed size, it is the ratio between the diaphragm opening and focal length. For a wide-angel lens with focal length 16mm, an aperture of f/8 will give you an opening of 16mm/8=2mm. A tele- zoom with focal length 500mm at the same aperture will give you an opening of 500mm/8=62.5mm. The basis of aperture values is f-number 8, i.e one eighth of the focal length. The aperture values we use today, was agreed to at an international congress in Paris in 1910.
The focal length is presented in millimetres. This is the distance from the last convex lens to the focal point. If you hold a magnifying glass so that the sun shines through it, you get a point where the rays come together. This is the focal point. The distance from the magnifying glass to the focal point is called the focal length. The focal point of the lens (objective) is where your image is in focus, i.e. where an object is rendered sharp. As long as the rays stay fairly close together, the image will record as sharp. This is what we call Depth of Field (DOF). From the drawings below you see this demonstrated. In Figure 1 you have a small aperture and low dispersion of the rays, i.e. longer DOF.
In Figure 2 the aperture is wide open, causing a large dispersion of the rays and a limited DOF. The sharp area behind the focal point is twice the size of the area in front of the focal point.
The standard f-stop (aperture value) scale
Each element in this sequence is one stop lower than the element to its left and the key figure is the square root of two (1,414). Multiply or divide by this figure to get one full stop up or down. The values are rounded off to more conventional numbers.
f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, etc.
By opening up a lens by one stop allows twice the amount of light to pass through to the sensor. In order to maintain the exposure, you need to double the shutter speed ( i.e. the shutter is open for half the time). In other words, if you are shooting at f/8 with a shutter speed of 1/125s, you will get the same exposure by using f/11 and 1/60s, or f/5.6 and 1/250s. Keep in mind that changing the f-number will influence on the DOF. In addition to the aperture, the focal length and the distance to the subject also influence on the DOF.
Modern cameras often utilise fractional steps, and the most common is steps of one-third stop (1/3 EV). The scale would then look like this:
…. f/2.8, f/3.2, f/3.5, f/4, f/4.5, f/5, f/5.6 …..
The elements in the timescale correspond with the aperture values. One full stop in the time scale, is either double the time or half the time, depending on you stepping up or down.
Here is an example of combinations that will give you the same exposure:
Time: 1/500 1/250 1/125 1/60 1/30 1/15 1/8 1/4 1/2 1/1
f-number: 1,4 2 2,8 4 5,6 8 11 16 22 32
In most cameras today you have the opportunity to choose either Aperture priority, or Shutter priority. As the name indicates, using Aperture priority, you adjust the Aperture value (f-number) as you like, and the camera will adjust the shutter speed accordingly to maintain the same exposure. For Shutter priority, you can change the shutter speed, and the camera will find the corresponding Aperture value.
For action photography, you should use a high shutter speed. If you photograpgh in low light conditions, you need long hutter speed. Using low shutter speed when shooting moving subjects, will cause them to blur. This is often used deliberately when photographing water to make it look soft.
In addition to Aperture, Focal Length and Shutter Speed, you have a forth factor you need to consider – the ISO Speed. The ISO rating describes the sensor’s ability to absorb light. Higher number means more quickly. What actually happens, is that the light is amplified. Unfortunately, it also amplifies undesired noise. If you need the quicker ISO speed, you will also get more noise in you picture. By doubling your ISO Speed, you will gain one full stop. When shooting in low light conditions, the ISO Speed can help you get the desired Shutter Speed and Aperture, but again, mind the noise!
Remember to set your ISO Speed back to normal when finished shooting in low light.
Enjoy your shooting!