A camera doesn’t take a picture, arguably it records light through the lens. In 1666 Issac Newton was carrying out an experiment using a prism in a darkened room, allowing the only light, sunlight, to enter the room through a small hole made in the window shutter. This was directed onto a prism which resulted in a multicoloured band of light to be produced. This experiment showed that there are varying levels of light. The first person to use the word photograph was Sir John F.W. Herschel in 1839. The word comes from the Greek words, photos (“light”) and graphein (“to draw”). So drawing by light is what the camera does, or as we know it today, thanks to Sir John F.W. Herschel, we take a photograph, and as Issac Newton discovered, there are varying levels of light.
In photography the amount of light that enters the lens is the exposure. Basically, how much light is exposed and recorded. Getting the right amount of light or exposure is important as this will determine how much information is recorded. It can be the difference between a really good image or a bad one. Too much light and the image will seem burnt out with the detail lost, too little and the image will be dark. Although it must be noted, when shooting in RAW, more information is recorded. This means that although an area looks burnt out, you will be able to recover more of the image as the recorded levels of brightness are increased. More levels of light equals more information.
Getting the exposure right can be difficult. In most of today’s digital cameras, there is a histogram that can be a valuable tool.
The histogram can be used to reduce some of the problems associated with exposure. In my cameras, I can use the histogram when taking or setting up a shot. It highlights the light and dark areas of the shot. I can then use the exposure compensation button (+/-) to add or reduce light recorded. The histogram is represented by a graph that will change shape as you move the camera around, Ideally a bell shape is what you are aiming for. In the first image above there are two peaks, these identify both sides of the fruit bowl, and the kitchen roll in the middle. There is also a semi light area to the right, depicted in BLUE in the histogram, this is actually a grey coloured battery charger behind the fruit bowl, but most histograms are only black and white.
The images above where taken one after another, seconds apart on automatic setting, yet the histogram shows that the level of exposure changes with every shot. The automatic setting compensates for slight movement, although the 3 images look the same, they are not, the histogram does not lie!
Below are these 3 shots showing their individual histograms. When compareing the histograms from each image you can see the slight changes. This give food for thought. When taking photographs out doors, and a cloud comes over, what happens to the exposure level???? hmmm
Below are the screen shots showing the properties of each of the shots taken, although no changes were made to the camera settings, and the exposure is the same, the size of P1220845 is .5mb larger than the other two, which means that there is more information in this image, the histogram will reflect this
Below are further shots taken
http://digital-photography-school.com/how-to-read-and-use-histograms/ – An interesting site