What is ISO in photography?

ISO stands for the International Organisation for Standardization. What does this mean?  It's a standardization that was introduced to film rolls before the days of digital cameras, and refers to how sensitive the film was to light. So ISO is all about exposure to light and how bright or dark your photo will be.

Low light sensitivity film (low ISO) had to be exposed for a long time in order to get a photo with a reasonable amount of light registering, whilst high sensitivity film (high ISO) only needed to be exposed for a short duration.

It's pretty much the same thing with digital ISO, which you can control for every shot. Changing the ISO settings changes the camera's light sensor's sensitivity to light. The higher the ISO the more sensitive the sensor is to light and the brighter your photo will be.

ISO usually ranges from 100 to about 3200.

Benefits of low ISO
When should you use low ISO? What are the benefits of low ISO?

• It's handy for outdoor shots and shots where there is already sufficient light present. Using flash and/or other special lighting devices allows you to use a low ISO whilst maintaining enough light in your photos.   If you have low ISO and insufficient light, increasing aperture and exposure time also helps (i.e. set your camera to a slow shutter speed). You can also use a tripod to help you use slower shutter speeds to maintain a lower ISO.
• Low ISO gives better quality shots: The lower the ISO the better quality the image will be, so as a general rule of thumb, you should aim to use the lowest ISO possible. This enables you to blow up the picture to larger sizes and still maintain better quality. When you use high ISO, the picture is at risk of appearing grainy or speckled because ISO introduces "digital noise" to the photo. It generally creates an effect that isn't as clean and sharp as you'd perhaps like and take note that this graininess is often not perceivable when looking at your shots through the LCD screen after shooting, but it will be noticeable when you upload your pictures and scrutinize them on your computer. Good cameras should exhibit less digital noise, but even the best cameras probably have some at high ISOs.

Benefits of high ISO
When should you use high ISO? What are the benefits of high ISO?

• It's useful in indoor situations where there isn't as much light, or in generally darker situations where you need to boost light but aren't allowed to use a flash or lighting devices.
• If you want to create a grainy, speckled effect in your photos, you can use high ISO to achieve this. Some photos look better with grain, although there are post-editing programs that allow you to create this effect on photos too. 
• It's useful for when you need high shutter speeds and you need as much light sensitivity as possible without allowing for it with shutter speed exposure. High shutter speeds may be important if you're holding the camera on a very wobbly surface (e.g. from a moving vehicle), or if you're trying to photograph a still shot of a moving object.
• If you know you need a low quality, small image and grain doesn't matter, increasing ISO can be a quick-fix for getting the lighting right.

What is exposure? Camera exposure explained

Exposure refers to how much light enters the camera when you shoot a picture.

If there is optimal exposure, the amount of light that enters is just right (which is subjective according to the effect you want to achieve).

If there is over-exposure (too much exposure), your image will have too much light in it and is likely to appear very bright and white. This is sometimes said to be "washed out". With extreme over-exposure the whole thing can appear just white. Sometimes you want a picture to be more white than it actually is for effect, or to lose details on purpose.

If there is under-exposure your image will have too little light in it and will likely appear very dark. With extreme under-exposure the shot can be virtually completely black. Sometimes a photographer desires darkness to get a certain look.

Factors that effect exposure

Exposure depends on two main factors:

1.) Aperture - The larger the aperture, the more light can enter the camera and the more exposed the picture will be. Large aperture gives high exposure and small aperture gives lower exposure.

2.) Shutter Speed - This refers to how long you leave the shutter open to capture the light before you take a shot. If there is a really fast shutter speed there is little time for light to enter and the picture appears less exposed. At longer (slow) shutter speeds there is more time for light to enter and the image has greater exposure.

Adjusting the shutter speed affects what's known as "exposure time", and this tool can be used not only to manipulate how bright or  dark a shot is, but it can also be used to capture movement in unusual ways. When the shutter is open for a long time to record a shot, if the shot is moving in this time, it captures the motion blurs brilliantly. Conversely, if you have a short shutter speed, it creates a sharp shot of the thing in motion - like a sharp snapshot of a moment in time with no motion blurs.

3.) ISO - This is an artificial manipulation of how sensitive your camera is to light for a particular shot.

What is aperture?

What is aperture in photography?

Aperture definition:

The aperture is the the hole in the lens through which the light enters the camera.

Although the lens has a constant diameter, the hole through which the light enters can be varied by the opening or closing of a "shutter" which, like the iris of the eye, makes the hole smaller or larger. In the metaphor where the shutter is the iris, the aperture is the pupil.

Opening the aperture allows more light in, and the more light there is we say you increase the "exposure", and the picture looks brighter or whiter. Opening the aperture also decreases the depth of field (i.e. it decreases the focus range so that only the things at one focal point are sharp and things in other focal points are blurry. For example if the focus is on the foreground, the foreground will be sharp but things in the background appear blurry).

Closing the aperture allows less light in, so this decreases the exposure and makes the picture look darker. Closing the aperture also increases the depth of field (i.e. it increases the focal range so that whether things are close or far away they appear sharp).

How do you change the aperture?

To change the aperture size you need to change the F-number (where F stands for focal length).

What is "focal length"? It is the distance (measured in millimeters) from the center of the camera lens to the focal point of the image (ie, the "image sensor surface").

The F-numbers can range from 1 to 16, although my camera only rangers between F2.4 and F8.0 which I guess means that the maximum distance my camera lens can go from the image sensor surface is 8mm? I need to check this! More sophisticated cameras can have a greater focal length capability.

You can also buy special lenses that have shorter focal lengths of longer focal lengths.
- Short focal length lenses = wide angle lenses
- Long focal length lenses = telephoto lenses

I mentioned above that when you set the camera to have a large aperature there is decreased depth of field. Another way of saying this is that there is an inverse relationship between F-numbers (focal length or depth of field) and aperture size.

To decrease the size of the aperture (i.e. to allow less light in),  you want the F number to be  large. The larger the F number the smaller the aperture. So the larger the F number the darker your picture will appear.

Similarly to increase the size of the aperture (i.e. to allow more light in), you want the F-number to be small. The smaller the F number the larger the aperture and the brighter and more exposed your picture will be.

How do  you change the F-number? 

I suspect you may need to check your camera user manual for how your specific camera works. On my camera (Canon PowerShot Pro 1) you have to set it to manual setting (M) and fiddle around with a dial to change the F-number.