A Brief Guide to Setting your Camera

Every camera is different, and each camera has different modes.  We will be looking at only a few of those modes and what they do.  We will go into a little bit of detail about each mode and when to use it.  
But first:

What is Shutter speed?
Put simply,  the shutter speed is how long the sensor (or film) of the camera is exposed to the light from the scene. We measure shutter speed in how much of a second the sensor is exposed to light, so for example 1/60 means that the sensor is exposed to the scene for 1/60th of a second. Generally shutter speeds range from 30 seconds to 1/4000th of a second.  

Practically this means that the longer the shutter speed the more light we get in the shot.  But this means that the subject has time to move, so a long shutter speed will make the picture more blurry.  If we are taking a picture of something moving we will need a faster shutter speed than if it is not moving.

We also need to take into acount how much the camera shakes, so if the camera is on a tripod we can get away with a much longer shutter speed than if we are just holding the camera.

Slower shutter speed = more light and more blur
Faster shutter speed = less light and less blur

What is Aperture?
Put simply, the aperture setting controls how much light we let into the camera when we push the shutter button.  We measure aperture in "F stops" so you will see for example F2.8 or f/2.8. Generally compact cameras range from f/2 to f/8, and with SLRs the lenses can range from f/1.2 up to f/32.

Practically this means that the wider the aperture (the lower the number) the more light we let into our shot, but the lower our depth of field (how much of the shot in front of and behind the subject is in focus).

Depth of field also scales with the size of the subject, so if we are taking pictures of small things the depth of field will be more restricted.

Low F stop = More Light but less depth of field
High F stop = Less light but more depth of field

What is ISO?

ISO stands for 'International Standards Organisation'.  The ISO sensitivity is a measure of the sensor's sensitivity to light.  A large number means that the camera is better at taking pictures in low light, but the downside to high sensitivity is noise.  Noise appears as graininess or spottiness in the picture.

Low ISO = Less sensitivity to light and less noise
High ISO = More sensitivity to light and more noise

Generally, we set the ISO to a value known to give a low level of noise, but if the available light is poor and we don't want to use flash, we turn it up.

Some reasons for not wanting to use flash are:
1) It's not allowed (museums, etc.)
2) It can cause red eye.
3) It can kill animals such as sea horses.
4) The subject is a long way away (it won't have any noticeable effect).
5) Natural lighting is wanted.
etc. etc.

Now lets look at the modes.  Here are the 5 modes that we will be looking at 
P Programable Auto
TvShutter Speed Priority (time value)
Av Aperture Priority (aperture value)
M Manual.

What do the modes do?

Each mode lets us control different aspects of the camera. 
In Auto the camera does all of the work for you.  
In P the camera lets you control the ISO, the scene modes, and the white balance.  Different cameras will have different things available but generally, P lets you control everything but the aperture, shutter speed, and the flash.  
In Tv we have access to the Shutter speed as well as everything that was accessed in P mode.  
In Av we have access to the Aperture as well as everything available in the P mode.  
In M we have control over the Aperture, Shutter Speed and everything available in the P mode, we also get control over the flash output of the camera.

So when do I use each mode?
 As Auto is so similar to P just with less control we tend to prefer not to use the Auto mode.

P  We tend to use P when we don't have very long to take the picture (although if the reason we don't have time to take the picture is because the subject is moving very fast then this is not the right mode to use).  Another reason for using P is because we would be doing exactly the same as P would do if we were using another mode.

Tv   We use Tv when control over the shutter speed is most important .  Most of the time we want control over the shutter speed so we can force a high shutter speed (to de-blur fast moving subjects, or to overcome camera shake).  

Av  We use Av (aperture priority) when control of the depth of field is most important.  A large aperture (low F number) means that objects closer than and further away than the main subject appear to be out of focus.  If you want as much as possible to appear sharp, you need to use a small aperture (large F number).  In fashion photography, the background is often made to go out of focus by using a large aperture.  In macro photography, we usually want everything to be sharp, so a small aperture is used.

M  We use M when we need control over the entire camera.
We set both aperture and shutter speed and use the camera metering to determine the exposure.

Exposure and exposure compensation
To decide how much exposure is needed, the camera must average the light coming from the scene in some way.  By averaging over different areas, it is possible to choose between metering that is best for small spots, or for small areas like faces, or for the whole scene.  Metering for the whole scene gives the best general-purpose result, but it is also easily fooled by unusually bright subjects in an otherwise dark scene; or by bright objects (or sky) in the background of an otherwise normal scene (back lighting).  Exposure compensation is used to correct for metering errors caused by back lighting or by very bright subjects.

 If the subject is back lit, standard metering will make the foreground dark.  Increase the exposure to make the foreground lighter.

If the subject is bright or luminous against a dark background, standard metering will cause it to be bleached white (over exposed) in the picture.  Reduce the exposure to make the subject darker.

An alternative to using exposure compensation is to select a spot or small-area metering mode and meter on the main subject.