Tips: Choose the correct aperture

1. Match the aperture with the object and the goal of your pic. If you wanna shoot a landscape, use small aperture like f/16 or smaller (f/22, f/32).
2. Balance aperture and shutter speeed, to make perfect exposure.If the light is strong enough, usually the shutter speed is also high, so use small aperture.
3. To choose aperture you also should think about what ISO do you use.
   

Exposure

Exposure is the total amount of light allowed to fall on the photographic medium (photographic film or image sensor) during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance. A camera uses two things to control the amount of incoming light (exposure):

A. Shutter:
In a camera, the shutter blocks all light from exposing the film UNTIL you press the button.Then it quickly opens and closes, giving the film a brief flash of light. You can control the length of time the shutter remains open by setting the SHUTTER SPEED.

Examples:
- A half second exposure is ONE STOP darker than a one second exposure.
- A 1/125 exposure is TWO STOPS brighter than a 1/500 exposure.
- A 1/1000 exposure is THREE STOPS darker than a 1/125 exposure.
- The longer exposures ( like 1 second ) give much MORE light to the film than a 1/1000 of a second exposure. So even though the number may look bigger, don't be deceived!

B. Aperture:
When light passes through a camera's lens, it must pass through an opening called an "Aperture". In plain english it's a hole that lets in more light when it's wide open and less when it's small. Figures, huh? In essence the aperture is just like the pupil in the human eye. You can control the aperture by setting the "Aperture Opening", also known as an F-Stop. To control how much light is passed through the lens.
Examples :
- f/4 is wider than f/16
- f/32 is narrower than f/8

What is ISO???

International Standarts Organizations (ISO), used to known as ASA, is how sensitive the image sensor is to the amount of light present. The higher the ISO, the more sensitive the image sensor and therefore the possibility to take pictures in low-light situations.

ISO Speed & Exposure

ISO speed affects the shutter speed / aperture combinations you can use to obtain correct exposure.

Suppose your digital camera's light meter warns you there is not enough light to correctly expose a scene. You could use the on-board flash, but let's suppose again it's not allowed (like in a concert or indoors recital).

You would then need to use a higher ISO. Set on "ISO Auto" mode, your digital camera will automatically select a higher ISO. Otherwise, you can manually select the next higher ISO and see if the increased sensitivity allows you to obtain a correctly exposed picture. If it does, you can now take a correctly exposed picture.

Similarly, if you find the camera is using a shutter speed that is too slow (1/60 sec. and slower) to handhold the camera steady and shake-free (thus resulting in blurred pictures), and you cannot open up the aperture anymore, and you do not have a tripod or other means to hold the camera steady, and you want to capture the action, etc. etc. -- then you might select the next higher ISO which will then allow you to select a faster shutter speed.

ISO Speed & Noise

However, all this increase in sensitivity does not come free. There is a price to pay with your image appearing more noisy.

See, when you boost the sensitivity of your image sensor by selecting a higher ISO, the image sensor is now able to record a fainter light signal. However, it is also true now that it will record fainter noise, where noise is any signal that is not attributed to the light from your subject. Remember that an image sensor is still an analog device and it generates its own noise, too! The increased sensitivity allows the image sensor to record more light signal and more noise. The ratio of light signal to noise (S/N ratio) determines the "noise" in your resultant image.

An image sensor is usually calibrated so that it gives the best image quality (greatest S/N ratio) at its lowest possible ISO speed. For most consumer digital cameras, this value will be expressed as ISO 50, ISO 64 or ISO 100. A few digital cameras use ISO 200 as their lowest ISO speed.

Just as with its film counterpart, an image sensor will exhibit "noise" (comparable to "graininess" in film) at the higher ISO speeds. Unlike film, where graininess can sometimes contribute to the mood of the image, noise produced by an image sensor is undesirable and appears as a motley of distracting coloured dots on your image.

What is Photography???

Got it from Wiki......

Photography (IPA: /fә'tɑgrәfi/ or /foʊ'tɑgrәfi/) is the process of recording pictures by means of capturing light on a light-sensitive medium, such as a film or electronic sensor. Light patterns reflected or emitted from objects expose a sensitive silver halide based chemical or electronic medium during a timed exposure, usually through a photographic lens in a device known as a camera that also stores the resulting information chemically or electronically. Photography has many uses for both business and pleasure. It is often the basis of advertising and in fashion print. Photography can also viewed as a commercial and artistic endeavor.

The word "photography" comes from the French photographie which is based on the Greek words φως phos ("light"), and γραφίς graphis ("stylus", "paintbrush") or γραφή graphê ("representation by means of lines" or "drawing"), together meaning "drawing with light." Traditionally, the product of photography has been called a photograph, commonly shortened to photo.