Cameras share some common features:

a lens,

a light tight body,

a light sensitive medium (film or sensor) to capture the image.

a lens aperture which controls the amount of light reaching the medium

a shutter which opens and closes to allow light to act for a specified time

a viewfinder or screen on which you can see the picture you will take

there are 2 functions on the camera that you use to take a photograph

Aperture

The aperture is just a hole whose size can be varied to allow more or less light to pass through it. The size of apertures are expressed in f-numbers.

The range of f-numbers follows a standard sequence with each f-number being half as bright, passing half as much light, as the previous one.

f 1.4; f 2; f 2.8; f 4; f5.6; f 8; f 11; f 16; f 22; f 32

The difference in value between one full f-number and the next is known as a 'stop'

Shutter and Shutter Speeds

The shutter prevents light from reaching the film until the moment of exposure, when it opens for a predetermined time allowing light passing through the lens aperture to reach the film. Unlike the aperture, which is always in an open position the shutter is always closed. Shutter speeds are expressed in seconds or fractions of a second

1sec; 1/2sec; 1/4sec; 1/8th; 1/ 15th; 1/30th; 1/60th; 1/125th;

1/250th; 1/500th; 1/1000th; 1/2000th

As you may have worked out, changing from one shutter speed to the next changes the exposure by one 'stop' in much the same way as changing the aperture.

F2.8 @ 1/500s

f4 @ 1/250s

f5.6 @ 1/125s

Most camera's have Shooting modes which allow you to change the aperture (Aperture priority) or shutter speed (shutter priority) and the camera will meter the light and set the shutter speed (if in AV) or aperture (if in TV). There will also be a full manual control on most too along with a full auto or Program AE mode. Auto is a purely point and click mode which allows no adjusment with Program AE usually allowing small adjusment. Most of the time I use AV or TV depending on the type of photo I am taking (more of This later).

ISO speed

On digital camera's this ISO speed is the sensitivity of the sensor.

100 200 400 800 1600 3200 for my 20D

When in AV mode increasing the ISO from 100 to 200 increases the shutter speed by 1 stop

ISO 100 = f2.8 @ 1/100s

ISO 200 = f2.8 @ 1/200s

when in TV mode you increase the aperture by one stop when you up from 100 to 200 iso

ISO 100 = 1/100s @f2.8

ISO 200 = 1/100s @ f4

if you increase from 100 to 400 you increase by 2 stops.

The down side to this is noise. Noise is like snow on a TV screen.

ISO 100

ISO 400

ISO 1600

Pictures courtesy of http://www.dpreview.com

Using these 3 functions allow the photographer to get the photograph he wants.

Control of aperture

To control aperture is to control depth of field (DOF). DOF is the area in focus. In this picture you can clearly see the DOF (the bt of carpet in focus) for the given aperture (f2.8). the blur in the background is called Bokeh

However this Picture was taken at a relatively close shooting distance. This close proximity to the target gives a shalow DOF. Taking a picture of an object further away increases the DOF at the given aperture and focal length (focal length is decribed in mm). The smaller the aperture (higher f number) the larger the DOF you'll get.

Small DOF is good as it makes your subject stand out

however particularly with closer (macro)shots you need a greater DOF to maintain the whole subject in focus. This particular shot was at f11 and you can see some of it is still not in focus

It all depends on where the subject is in relation to the plane of focus. a macro shot of a bug longways like above requires more DOF compared to a side ways macro of a bug.

Control of shutter

Shutter speed is important for blur and camera shake. if you are using a lens at 200mm but are using a low shutter speed (1/60s) your more than likely to get camera shake and a bluring image.

The rule of thumb is to use at least 1/focal length as a shutter speed. e.g 200mm focal length min shutter speed 1/200s.

Shutter speed is used to control movement. A high shutter speed will capture a fast moving object and make it look sationary.

while slow shutter speed will induce background blur while hopefully capturing the target.

Slow shutter speed (TV mode 1/20s)and moving at same speed as target.

slow shutter speed (TV mode 1/50s target moving at 20mph) and panning (follwing target with camera)

Slow shutter speed can also be used to make light trails

or make water look sliky

Expsure compensation

Most people do not have hand held light meter to take a reading (meter) of the subject and set the camera manually to get the correct exposure they want. Most camera have various types of metering modes which allow you to meter the light to give different exposures.

Evaluative - This mode takes the average from several different points ( my 20D has 35).

Partial - on most camera this mode takes the meter reading from the center of the view screen (on my 20D it is 9%)

Center-weighted average - this averages out the light reading from around the center of the view screen. I reads more than partial.

Spot - this takes a reading from a particular spot which is usualy around 2-4% in size compared to the view screen.

However the camera can be fooled when if there is a particular bright or dark portion of the composition. This can cause either overexposure (bright) or underexposed (dark) image. This can be used in either TV or AV mode. In TV mode the shutter speed stays the same with the aperture increasing or decreasing and in AV mode the aperture remains constant with shutter speed increasing or decreasing. On my 20D I have 2 stops of compension +/- from the meter reading and can be adjusted in 1/2 or 1/3 stops.

Exposure compensation is required when shooting snow.

No compensation

+2/3 stop

+1 1/3 stop

White balance

White balance [WB] is the colour temperature of the image and is measured in kelvin (k). The adjustment of white balance is required depending on the light source which is illuminating your subject. the sun has a different value compared to a flash or indoor strip lighting. Most cameras will have basic settings (photo shop CS RAW settings)

Nice Im clueless at photography and that sort of guide is very useful for making me think about it a bit more. Cheers

Brilliant guide well done mate. Fully comprehensive! Big thumbs up. thanks for taking the time out!