How does it happen?
After writing last week's post, banging on about shooting film, it occurred to me that many of you may never have seen, let alone used a film camera. So this week I will attempt to explain how it all works and demonstrate how the "old" technology of film directly relates to today's digital.
First up, let me explain the "bits" of an SLR (single lens reflex) film camera (I'm going to use the Fujica as my model).
A: Film rewind lever. As suggested is used for rewinding the film. On most cameras, by lifting the winder you also release the catch that fastens the back door.
B: Film canister goes here.
C: Shutter curtain. (some have blades)
D: Winding sprocket. The sprocket wheels (top and bottom) engage in the sprocket holes in the film.
D: Film take up spool. As the film is advanced it is wound around the spool.
F: Pressure plate. Holds the film flat to ensure correct focus.
With a modern digital SLR the film is replaced with a sensor, and the electronics (and battery) fill the void left when the film and advance mechanism are removed.
This diagram illustrates the path light takes through a SLR camera.
One of the positive selling points of an SLR is that you see exactly what the camera sees ... you are viewing directly through the lens. Light enters through the lens is reflected by a pivoting mirror (1), through the focussing screen (2) into the pentaprism which directs the light to the viewfinder. The prism also ensures the image is viewed right-side-up.
Three elements determine the exposure of the image; ISO, shutter speed and aperture.
ISO relates to sensitivity ... the light sensitivity of either the film or digital sensor. Unlike the digital cameras of today (where the ISO can be changed at any time) once a film is selected and loaded its ISO is locked.
Shutter speed refers to the amount of time the shutter is open, allowing light through to the film or digital sensor. It is usually expressed as fractions of a second e.g. 1/60th, 1/250th, 1/8000th (of course longer durations are also possible).
Aperture is the variable opening within the barrel of the lens. The size of the opening (aperture) is adjusted via a diaphragm constructed of blades. The various stages of constriction are called f-stops (f4, f8, f16). The larger the f-stop, the smaller the opening ... confusing until you come to grips with it.
If you understand the basic mechanics of how a camera works and the science of exposure, you have a much better chance of improving your photography. If you are just letting the automatics of the camera (be it an expensive DSLR or an iphone) do the work, is it really you who is making the photograph?