About AE and AF

AE : Abbreviation for auto exposure. This key feature automatically sets the aperture and shutter speed.

AE Lock : During AE shooting, you can lock the aperture and shutter speed settings. With AE lock, you can use the same aperture and shutter speed even if you change the composition or even if the light changes. When you press the shutter button halfway, AE lock and AF lock take effect.

AF : Abbreviation for auto focus. The camera focuses automatically.

AI Focus AF : The camera switches automatically from One-Shot AF to AI SERVO AF when necessary.

AI Servo AF : AF mode for continuous autofocusing on a moving subject. This mode predicts the next movement of the subject so that the focus is correct when you take the picture. This is also called predictive AF.

Causes of Noise

There are a number of sources of noise contamination.

Heat generated might free electrons from the image sensor itself, thus contaminating the “true” photoelectrons. These “thermal electrons” give rise to a form of noise called thermal noise or dark current.

Another type of noise is more akin to the ‘grain’ obtained by using a high ISO film. When we use a higher ISO, we are amplifying the signal we receive from the light photons. Unfortunately, as we amplify the signal, we also amplify the background electrical noise that is present in any electrical system.
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Exposure Bracketing

Exposure bracketing is a simple technique professional photographers use to ensure they properly expose their pictures, especially in challenging lighting situations. When you expose for a scene, your camera’s light meter will select an aperture / shutter speed combination that it believes will give a properly exposed picture.

Exposure bracketing means that you take two more pictures: one slightly under-exposed (usually by dialing in a negative exposure compensation, say -1/3EV), and the second one slightly over-exposed (usually by dialing in a positive exposure compensation, say +1/3EV), again according to your camera’s light meter.

The reason you do this is because the camera might have been ‘deceived’ by the light (too much or too little) available and your main subject may be over- or under-exposed. By taking these three shots, you are making sure that if this were ever the case, then you would have properly compensated for it.
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Aperture

The main function of a camera lens is to collect light. The aperture of a lens is the diameter of the lens opening and is usually controlled by an iris.The larger the diameter of the aperture, the more light reaches the film / image sensor.

Aperture is expressed as F-stop, e.g. F2.8 or f/2.8. The smaller the F-stop number (or f/value), the larger the lens opening (aperture).

[Note: Many camera user manuals today will refer to the aperture in terms of "aperture value" instead of f/value. I'm not sure when this trend started but don't get confused between "aperture" and "aperture value." Aperture value" is simply another way of saying f/value.]

In practice, unless you are dealing with a fixed-aperture lens (many simple point-and-shoot cameras have only one fixed aperture), the aperture of a lens is usually expressed as a range of fstops.
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