This is for camera owners whose cameras have never been off the Automatic setting to explore the series of letters on the dial. By “Automatic setting” I mean both the “just point and shoot” green box position and the so called “scene modes” that the camera maker labels with little icons for close-up (usually a flower), portrait (head), sports (running man), landscape (mountains) and the like. I have one camera with dozens of these scenes available, even down to settings for parties, snow and food! Now, whether you set these by turning a dial or through a menu, they all work by altering just 5 settings in your camera: White Balance, Focus System, Shutter Speed, Aperture Value and Flash. I won’t deal with most of these controls in this Intel beyond mentioning what each is or does.
White Balance adjusts for the colour of the light falling on it. It is the equivalent of human sight’s ability to see paper as white even if we turn off the neon and turn on the tungsten light - fluorescent is green, tungsten is red, yet the paper is still white to us.
Focussing Systems move elements in the lens until the part of the subject in the focusing area attain maximum contrast. They can operate in various modes, the main ones being “single shot” which locks the lens as soon as focus is found; and “servo assisted” which continuously attempts to keep the lens focussed on the subject as it moves. Other modes tend to be variations and combinations of these two.
Flash is offered on most cameras and usually includes settings to reduce red-eye (reflections from the retina of the eye), general flash and special modes like “night portrait”, where a flash exposure is followed by a longer exposure to capture first the foreground then the darker background. Most cameras will also allow the flash to be disabled, and some cameras with a particular type of shutter will allow you to choose whether the flash fires as the shutter begins to open, or as it closes.
The most important controls are the Shutter Speed and Aperture settings. Understanding these two aspects of photography marks the difference between a snap-shooter and a photographer.
For this paper I want to focus on aperture. I will devote another Intel to the shutter. Once you have read both, you will never want to go back to “green box”, auto or any of the funny symbols again - well, hardly ever. You will be master of M, Tv, Av and P: manual, shutter priority, aperture priority and program.
There are two settings on your camera which allow you to directly control the aperture of your camera, but every manufacturer uses their own abbreviations for them. The first is the Manual setting, which lets you change both the shutter speed and the aperture. It is almost always marked M or MAN. We won’t be addressing Manual Mode today. The second is Aperture Priority Mode.
Aperture Priority Mode is marked Av on some cameras, on others, A, and on a few, dep, suggesting “depth of field control”. For convenience, I will use the term ‘Av’.
When the dial is set to Av, you choose the aperture, and the camera automatically sets a shutter speed to provide the correct exposure. It can do this because the relationship between the aperture and the shutter speed is fixed: halve the aperture and you need to double the shutter speed to allow the equivalent amount of light to reach the sensor or film (from here on I will just refer to the sensor, but it applies equally to film). So what is this aperture ?
Inside each lens are a series of blades that can open or close. This lets the camera adjust the size of the hole that the light comes through when it enters the camera. This hole is called the aperture and it is a lot like the iris in your eye.
Obviously, a fast shutter speed will require a larger aperture to ensure sufficient light gets through, and a slow shutter speed will require a smaller aperture to avoid excessive exposure.
Originally apertures were circles cut from pieces of thin material. My first camera was fitted with a metal slide in which different sized apertures were punched. To set the aperture, you slid the appropriate hole in front of the lens. Today a device called a ‘diaphragm’ is used to control the effective diameter of the lens opening, opening and closing like an iris.
Why is it useful to control this iris manually rather than just letting the camera get on with it? Because the aperture controls the depth of field. It lets you control what, and how much of the photograph is in or out of focus, and if out of focus, by how much! That is creative control!
In general, the smaller the aperture, the greater the distance from the plane of focus the subject matter may be while still appearing in focus. Need more depth of field? Set a smaller aperture. Background distracting? Choose a larger aperture.
The size of the lens aperture is referred to as an f-number, and confusingly, large f numbers refer to small apertures and vice versa. This is because the f/number is a ratio between the focal length and the aperture diameter.
Think of it as a fraction if it makes it easier to understand: when you see f/22 it means ‘focal length divided by 22’, and that has to give a smaller answer than ‘focal length divided by 4 - 1/22 is smaller than 1/4.
The reason for this brief excursion into maths is to give you some way of stating what your opening (aperture) size is, and knowing how much to increase or reduce it. The numbering system seems pretty odd at first. It goes …f1.4, f2, f2.8, f3.5, f4, f5.6, f8, f16, f22, f32…
If you want to do the maths, each stop represent a √2 (approx. 1.41) change in f-number. This is because it is the area that the light falls on that is significant, not the diameter of the hole.
What is important about this is that it means that every time we increase the f stop by one step we halve the light reaching the sensor, and every time we decrease the f stop by one step, we double the light reaching the sensor.
So: go from f5.6 to f8 half the light (and therefore you just have to make the the shutter speed twice a long to keep everything in balance).
Your lenses are not likely to have all those f/stops available. When you buy a camera or a lens, you should ask the minimum and maximum apertures that the lens can achieve. The maximum aperture (minimum f-number) tends to be of most interest; it is known as the lens speed and is always included when describing a lens (e.g., 100-400mm f/5.6, or 70-200mm f/2.8).
Lenses with large maximum apertures (f2.8 or better) command a higher price: and are worth it.
A typical lens will have an f-number range from f/16 (small aperture) to f/4 (large aperture). Professional lenses for 35mm cameras can have f-numbers as low as f/1.0 The fastest lens I ever owned was a f1.4 Yashinon fitted to a Yashica rangefinder camera.These are known as "fast" lenses because they allow much more light to reach the film and therefore reduce the required exposure time.
Lenses which have a fixed focal length and large aperture are favoured by photojournalists and others who work in poor light, have no opportunity to introduce supplementary lighting like flash, and need to capture fast breaking events.
Zoom lenses typically have a maximum aperture that varies as you zoom out, becoming smaller and therefore passing less light at the telephoto end. A very fast zoom lens may have a constant aperture of, say, f/2.8 or f/2 throughout its range, which means its relative aperture will stay the same.. A more typical consumer zoom will have a variable relative aperture, since it is harder and more expensive to keep the aperture proportional to focal length at long focal lengths; f/3.5 to f/5.6 is an example of a common variable aperture range in a consumer zoom lens.
If you set your aperture too high or low and your camera cannot provide a matching shutter speed, you will get a signal (usually a flashing light or number in the viewfinder or on the LCD). If that happens, some cameras will stop you taking the photo until you get back in range, but others will just accept that that is what you want and let you over/under expose. Just keep your eye on the shutter speed to avoid that and to also avoid such slow shutter speeds that you won’t be able to hold the camera steady.
That’s plenty of theory. Now set your camera to Av and go take some pictures. Experiment with limiting the depth of field in your portraits or to hide a messy background, and stretch it way out to capture those sweeping vistas.
Next time We will grapple with Creative Shutter Control.
