Whether you are using a traditional film Single-Lens Reflex (SLR) camera, or a digital SLR (DLSR), you need to first understand some basic photography fundamentals in order to take good pictures.

The fundamentals are:

1) Exposure

2) Aperture

3) Shutter Speed

4) ISO

5) Metering System

6) Depth of Fields

7) Composition

We will discuss the first four fundamentals and how they are inter-related here in the context of digital photography.

Basically, Aperture, Shutter Speed and ISO together control how much exposure the sensor will receive, and thus the resulting image. You can also achieve the same exposure if you increase one of them and reduce the other one relatively.

Exposure is the moment when light strikes the sensor and the image is recorded.

Three factors combine to determine the correct exposure for a digital image:

a)      The amount of light in the scene strikes the CCD or CMOS sensor

b)      The length of time that sensor is exposed to the light

c)       The sensitivity of the sensor

 The amount of Exposure time will determine how much light will strike the senor and how much details will be recorded. The longer the exposure, the more light and details will be recorded. However, too much light will result in an overly exposed (totally white) picture.

In the other hand, too little light will result in an under-exposed (no details, or even totally black) pictures. So choosing the right setting for Aperture, Shutter Speed together with ISO is very important.

The camera, however, still give the photographer some control on the exposure to achieve certain effect through Exposure Compensation (EV), choosing a Negative (-) value will force the camera to adjust the exposure lower than the normal value. Choosing a Positive (+) will force the camera to adjust its exposure higher than it normally would.

An aperture is the variable opening in a lens that allows light through.

It is made up of a series of overlapping metal blades called an Iris diaphragm to allow the size of the aperture to vary from full diameter to small hole.

This variable opening determines the amount of light that falls on the sensor. The smaller the f-number (e.g. f-2.8), the bigger the aperture size.

 Aperture influences the shutter speed and the depth of field of a picture.

Under the same lighting condition & ISO setting, small aperture will require a longer shutter speed, while a big aperture will require a shorter shutter speed.

Big apertures like f2.8 or f4 have a shadow depth of field, which will produce a picture with foreground sharp, but the background soft/blur.

Smaller apertures like f22 have a greater depth of field, which will produce a picture with both foreground and background sharp.

Shutter is the device that opens and closes to control the time that light is allowed to pass through the aperture to the sensor.

It is measured in seconds and can range from 1/4000 for very fast camera to 15 seconds.

 Shutter speed control how moving image will appear in the picture.

Fast shutter speed will freeze moving action, while a slower shutter speed will create a “motion blur” effect.

It is the term used in the traditional film photography to indicate the sensitivity to light of the film roll. The higher the number, the more sensitive it is.

ISO 400 is twice as sensitive to light as ISO 200, and thus can perform better in lower lighting condition than ISO 200.

In DLSR, of course there is no more film used. Instead, the ISO setting will tell the sensor how to behave if it is a traditional film.

ISO will control how much how sensitive the senor will react to light and the quality of the image.

A low ISO will require more light and will produce a better quality image.

A high ISO will require less light but will produce noise in the image.

In a bright sunny day outdoor, use a lower ISO, like ISO 100 or ISO 200, while in low light condition, use a higher ISO setting.

If you want to learn more about Composition, you may want to take a look at the article Photography Fundamentals - Composition.