This is the question I get asked most frequently about photography. "What is exposure and how do I know which camera settings to use".

   The first question is pretty easy to answer but the second part is a little more difficult. The reason for this is because the answer is subjective. The settings you choose will have an effect on how the photograph will look in many different ways. I will attempt to answer both questions as effectively as I can. While parts of my answer may not be technically perfect, I think you will get the Idea.

Exposure

   Photographic exposure is the build up or recording of an image on a photosensitive (light sensitive) material or device by controlling the amount of light that the material or device is exposed or open to. 'Material' usually meaning photographic film and 'device' in this case meaning a digital cameras sensor. I hope that makes sense to you.

   It's important to realize that there are basically 3 controls to exposure. Two of them are camera settings but the third is the sensitivity of the recording media, whether it's photographic film or a digital camera sensor. This sensitivity is expressed as a numerical value usually with an "ASA" or "ISO" preceding the number.

   The numerical value used to express the sensitivity of photographic film or a digital sensor increases with the media's photosensitivity. As an example, ASA or ISO 100 is exactly half as sensitive to light as 200, 200 is half as sensitive as 400 and so on. Therefore it would take less light to create a good exposure on ASA 200 then it would to create a good exposure on ASA 100. I like to compare photographic exposure to filling a water bucket in my explanation. Lets just say that film was a light bucket. It would take twice as much light to fill an ASA 100 bucket as it would and ASA 200 bucket. Just remember that the higher the number the more sensitive the media.

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