Camera Jargon

Focal Length.
Focal length is determined by the lens you are using and is usually defined in millimetres. It basically describes the magnification of the lens. A focal length of 50mm is considered to be actual size (i.e. x1 magnification) and each additional 50mm of focal length increases the magnification by 1. So 100mm = x2 magnification, 200mm = x4, 300mm = x6, 400mm = x8, etc. Obviously for bird photography large focal length lenses are the best for the job, if not essential. Unfortunately they are also the most expensive.

Shutter Speed.
Shutter speed might seem obvious and I suppose it is. It is the amount of time that the camera exposes the film or digital sensor to the light. Faster shutter speeds are used for moving subjects as they enable the photographer to 'freeze' motion. As birds are very mobile high shutter speeds are usually essential.

ISO.
This is a numeric indication of the sensitivity to light. The higher the number the more sensitive to light. So in dull conditions choosing a higher ISO will give a brighter picture. However, the higher the ISO the more grainy (or noisy) the picture is. If you are still using film, then the ISO is determined by the film itself. If you put a 100 ISO film in your camera then you are stuck with 100 until it is used up. With digital you can adjust this for each shot to suit the conditions.

Depth of Field.
The depth of field describes how much of your picture is in focus. A narrow depth of field gives your subject in sharp focus and the background heavily blurred. A wide depth of field has both near and far objects in focus. Depth of field is controlled by the aperture.

Aperture.
The aperture is how wide the camera opens the shutter. A larger aperture allows more light and hence a brighter picture. It also gives a narrower depth of field. A smaller aperture gives a darker picture but a wider depth of field. The size of the aperture is denoted by the F numbers. The lower the number (e.g. F2.8) the larger the aperture whilst the larger the number (e.g. F5.6) the smaller the aperture. Lenses come with an F number, zoom lenses with a range of F numbers (e.g. F4-5.6). These numbers on your lens indicate the maximum aperture allowed for that lens. Using tele-converters reduces the maximum aperture further. When you are using the camera in full auto mode, the lens lets the camera know what it's optimum aperture value is. Of course, you can override this if you know what you are doing. For example, if you were using bright studio lighting you could reduce the aperture (increase the F number) for a wider depth of field and the 'darkening' of the image, due to the smaller aperture, would be compensated for by the very bright lighting.

Exposure.
Exposure is a term used to describe the brightness of the photograph. Too much light and a photograph is described as over exposed. The colours are washed out and details are lost. Too little light (more common) and the photograph is described as under exposed. The whole picture is very dark, may be even black, with details also lost. Under or over exposure on film means the picture is lost as there is nothing you can do about it. Mild under exposure with digital pictures can be corrected using photo editing software. Over exposure is more difficult, if not impossible, to correct. So it is better to slightly under expose your digital pictures than to over expose them. Exposure is controlled by shutter speed, aperture and ISO.

Metering.
Modern cameras use metering to determine exposure. The camera samples the light, dark and mid-tones of the subject and determines the settings to 'correctly' expose the picture. If you are using your camera in full automatic mode, this will include aperture and shutter speed. If you set the shutter speed manually, it works out the 'correct' aperture. If you set the aperture manually, it works out the 'correct' shutter speed. If you are in full manual mode, setting shutter speed and aperture yourself, it obviously does nothing. Now I've put the word 'correct' in inverted commas for a reason. In most cases where the image is a mixture of light, dark and mid-tones, it probably will get it correct. However, if the image is mostly dark (e.g. a black bird on a dark background) it will over-expose the picture. If it is mostly light (e.g. a white bird on a light background) it will under-expose the picture. So some manual correction will be needed. There are different modes of metering. Evaluative metering (sometimes known as matrix metering) is where the whole image in view is divided into zones. The camera works out what the main subject is, how it is lit, what the background light is like and works out the best aperture and/or shutter speed to expose the image. Partial or spot metering is where only a small area at the centre of the image in view is used to calculate what aperture and/or shutter speed to use. Centre weighted metering is where the whole image in view is analysed but greater emphasis is given to the centre of the image when calculating the aperture and/or shutter speed to use. This is normally the default mode on most cameras.

White Balance.
Light consists of three primary colours, red, blue and green. Some light sources have these colours in different strengths (unbalanced). Although our eye is pretty good at compensating for this in your photographs it can give your subject an appearance of unnatural colours. White balance can be adjusted on many SLR cameras allowing you to correct this if you are experienced enough to know how to get it right. If you are using digital cameras you can adjust this later with photo editing software if you need to, which is much easier to do if you take RAW format pictures.