How does a camera work
A camera can do lots of impressive things but understanding how it actually does these things may help you become a better photographer.
Imagine your sleeping in your bed and somebody comes in to your room and in haste, opens the curtains wide flooding the room with light. When this normally happens our eyes hurt and we rub them, what we are actually doing is putting them back into darkness allowing them to gradually get used to the sudden change in light. Our irises need to retract reducing the amount of light to enter into the eye. Too much light can damage the eye unlike a camera too much light will give an over exposed or washed out appearance.
The eye has to automatically control the amount of light that enters the eye in order to see a correctly exposed view. If you turn the light off in the the room that your in the room will get very dark very quickly. If we let our eyes adjust we can begin to pick out certain things within the room using the small amounts of light that are entering. This is because our pupils have registered that light is sparse and so it has expanded, the pupils have become bigger to allow more light to get in to the eye so it can allow us to see. The pause between this adjustment is the eye reacting to the conditions. As an experiment ask somebody to close their eyes. Once they do tell them to keep them closed for about 30 seconds. Make sure you're looking at their eyes, after the 30 seconds ask them to open their eyes - notice the pupil was big and then it retracted to adjust to the new level of light now the eye is open.
A camera can do all the thinking for you, if you set to auto. However if you want to be able to calibrate your camera for more specified jobs then understanding the sensor and it's behaviour towards light will enable you to understand your camera confidently.
Below is a diagram of a cameras workings, many variations of this diagram will represent one make or another but generally this is how an image is captured and light is harnessed.
 | 1. Lens 2. Primary Mirror 3. Primary mirror on exposure of sensor 4. Focusing Screen 5. Pentaprism 6. Eye piece Lens 7. Sensor 8. Sensor Filter(s) 9. Auto Focus System 10. Relay Mirror
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 | Under Exposed This image represents a very quick shutter speed, as you can see the shadows are quite prominent. The camera's sensor has not soaked up enough light to be able to give an accurate recording. The highlights within this picture are around the top right, this was bright enough for the camera to record as the sun was close to this spot. Great effects can be created by controlling the amount of light that hits the sensor. |
Over Exposed This is at the opposite end of the spectrum, light has burned the image to the sensor. The sensor is a plate made up of tiny buckets that fill up of photons which are light particles that bounce off objects. When the buckets become brimmed they overspill and the photons create large white areas within the recording. As you can see, detail has been lost on the path and in the sky, this is also known as being 'washed out'. |  |
To create this image I needed stability so I rested the camera on a fence post - you can see the fence to the right of the image. I had to experiment with varying shutter speeds as I had never attempted anything like this before. Eventually I created the effect that I needed using a shutter speed of 0.5 seconds. As you can see the image is on the verge of being over exposed but in the space of 0.5 seconds I was able to capture the effect of motion blur in a controlled area of the image. There are many possibilities for this effect and it is a great to see something uncover that you have created from the scenery around you.   |   I had to fix the image in photoshop - See how I did it |
