A photograph is an aspect of reality, and photography is about drawing a picture with the light of what is in front of the camera at the time.
A system camera is a light-proof box with an attached controllable light source.
The system camera is a combination of three basic parts, the aperture, the shutter and the ISO – The lens has the aperture, the camera body normally has the shutter and the sensor/film is ISO rated.
The lens is involved in focusing the light picture onto the sensor or film plane in the camera body, the aperture in the lens also controls the intensity of this light that reaches the sensor/film through adjusting the aperture by doubling or halving the intensity of light falling on the film/sensor in the camera body.
On the aperture ring on my lens, I have the options of f2 – f2.8 – f4 – f5.6 – f8 – f11 – f16. On my lens f2 is wide open and lets in the full amount of light that my lens can. F2.8 lets in exactly half of the light that f2 can, and so on through f4, f5.6, f8, f11 and f16 which admits the least amount of light on my lens. F11 admits twice the light as f16, f8 admits twice the light as f11 and so on to f2 which admits the most light on my lens.
The shutter protects the unexposed sensor/film from the ambient light around the photographer. The shutter in the camera body controls the length of time the sensor/film is exposed to the focused light coming in through the aperture in the lens. The shutter controls the time the film/sensor is exposed by doubling or halving the time the light is falling on the film/sensor in the camera body.
On the top of my camera body, I have shutter speed options of 1 – 2 – 4 – 8 – 15 – 30 – 60 – 125 – 250 – 500 – 1000. 1 is for one second, 2 is for half a second, 4 is for a quarter of a second and so on to 1000 which is for a thousandth of a second. Each shutter speed option like those of the aperture ring is double or half that of the preceding option.
The sensor/film is the third leg of the tripod that photography stands on. The first leg of the tripod is the aperture, the control of the intensity of light through the adjustment of the aperture in the lens. The second leg is the control of the time the light falls on the light-sensitive surface through the adjustment of the open time of the shutter. The third leg as said above is the light sensitivity of the sensor/film itself which like the aperture and shutter can also be doubled or halved in sensitivity to light.
The sensor/film is the light-sensitive surface that records the photograph of the subject that is in front of the camera at the time. Like the aperture and the shutter, the light sensitivity of the sensor/film can also be doubled or halved.
On the back of my camera body, I have the ISO options of 6 – 12 – 25 – 50 – 100 – 200 – 400 – 800 – 1600 – 3200 – 6400. Each ISO option is half or double the light sensitivity of the preceding or following as such, 50 ISO is half the sensitivity of 100 ISO and 200 ISO is double the light sensitivity of 100 ISO and half the sensitivity of 400 ISO and so on to 6400 on the one side and 6 at the other. 6400 ISO is my camera’s highest option, 6400 ISO is good for very low light situations where 6 ISO is good for very bright light situations. 400 ISO is a very good option for general light situations. As a narrative photographer, the 400 ISO sensor/film option is my go-to sensitivity for most of my work.
The tripod or three leg situation of aperture, shutter speed and ISO in photography gives the photographer a very wide choice of options for a perfectly exposed photograph in any photographic situation.
Photographic Basics is an extract from the first of 18 Zoom.us sessions, John Robinson offers these Camera & Coffee Sessions through his Zoom.us meeting room at R300 per session. Contact John on +27836547789 or firstname.lastname@example.org to book a session with him.