What is a digital camera?

Just getting started with digital photography? Our comprehensive guide covers the ins and outs of your digital camera in the first instalment of our Learning Centre series.

Let's start at the very beginning with the basic definitions that you'll come across when looking at digital cameras. A lot of the terminology will also be the same as 35mm film photography — so if you're familiar with analogue photography, never fear.

Digital cameras can be classified as either a compact (left) or SLR (right). (Credit: CBSi)

Though it sounds very basic, understanding what a camera is will help you understand how it works. The principle has remained the same since the beginning of photography — a camera captures light in order to form an image.

Put simply, light from the subject enters the camera's lens, which helps focus and direct the rays onto either the film plane or image sensor.

There are two main types of digital cameras: compacts and SLRs. We will be covering SLR cameras in more detail in our next instalment of the Learning Centre.

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What is a megapixel?

Resolution

Traditionally we would talk about resolution as just a count of the pixels.

pixels wide x pixels high
= resolution

As we will see later on, other elements of a digital camera (such as the lens and image sensor size) play a huge part in determining the true resolution that an image sensor can deliver.

A pixel is the smallest component that makes up a digital image. The megapixel value you'll find written on your camera simply means how many pixels (or photo sensors) are on your image sensor. The mega denotes one million.

A camera's megapixel count relates to the resolution of the image it is able to produce. Unless you are aiming to make very large prints of your digital images, more often than not a 10- or 12-megapixel sensor will produce a large enough file for you to work with for 10x15cm prints all the way to A3 size.

The table below shows the equivalent megapixel to resolution conversions. Note these are calculated based on a standard 4:3 aspect ratio — we'll explain this later when we talk about image sensors.

Megapixels Resolution
8MP 3264x2448
9MP 3464x2600
10MP 3648x2736
12MP 4000x3000

Get to know your camera

Now let's take a look at a typical digital camera. You may find yours has more or less of the elements that we've listed here. These are the main components:

(Credit: CBSi)

Lenses

The lens is arguably the most important part of the digital camera — after all, it plays the biggest part in making the picture. In principle, the lens of a digital camera works in the same way as your eye, opening and closing its aperture to adjust to changing light conditions. We'll be discussing aperture in full detail in our next instalment of the Learning Centre.

Most compact cameras on the market today will come with a variable focal-length lens (that means it can zoom in and out to get you closer to the action).

Definition: Focal length

Focal length is the distance between the lens and the image sensor when the lens is focused at infinity.


(Credit: CBSi)

The focal length also helps determine the field of view of a digital camera's lens, or what exactly the camera can see of a scene. As we'll see, the field of view increases or decreases depending on the focal length.


We often talk about the focal length of a lens in three ways, with measurements still left over from the days of 35mm film.

Wide angle

This covers any lens with a focal length of anywhere between 24mm to 35mm. This means the field of view is much wider, and essentially allows you to fit more of your subject in the frame. Super wide-angle lenses are characterised by their focal length being less than 24mm.


Standard

A focal length of anywhere between 35mm and 80mm is known as a standard lens. The happy medium is a 50mm lens which lets the camera capture a scene "as the eye sees it".

Telephoto

Lenses that have a focal length of over 100mm are telephoto. You can often tell just by looking at a photograph if it has been taken with a telephoto lens as these images often look like space has been flattened out, with less depth to them than if the photo had been taken with a wide-angle or standard lens.

Zoom

So how do you know what sort of lens your compact camera has? Often on the lens barrel you will find an indication of the focal lengths, though these will be written in the digital equivalents, not the 35mm equivalent like we've discussed above.

Check your camera manual under lens specifications as they will list the values in 35mm measurements. Most of the time your compact camera will come with a focal length that can vary between 35mm and 105mm. These numbers roughly equate to a 3x optical zoom. You'll find some compacts currently on the market come equipped with wide-angle lenses of 28mm or less.

Digital cameras will come with focal length measurements written on the lens, but they aren't 35mm equivalents. (Credit: CBSi)

Superzoom

A superzoom is what we call a "bridge" camera that looks almost like a dSLR but has no interchangeable lens.

The lens itself varies between an extreme wide angle to telephoto focal length, like on Canon's SX1 IS, which has a lens that extends from 28mm to 560mm.

(Credit: Canon)

On a compact camera, zooms usually range from anywhere between 3x to 10x. Extend the zoom reach to anything further and you start to enter into a different range of camera that is called a superzoom, or megazoom, with extreme telephoto lengths.

That said, don't rely on your zoom lens to do all the work for you. Some of the best photographs can be taken by using a standard focal length or what is known as a prime (fixed focal length) lens.

Renowned photojournalist Robert Capa put it aptly when he said "If your picture isn't good enough, you're not close enough."

Image sensors

The image sensor works with the lens and the image processor to create the final image. Covered in photosensitive pixels, the sensor reacts to the light passed through to it from the lens and forms the image by converting light into electrons.

First up, let's concentrate on the physical size of the sensor. In digital SLRs, the holy grail, if you will, of sensor size is full frame — equivalent to the size of a 35mm frame of film. For the sake of this discussion we'll exclude medium format professional cameras which are well beyond the scope of the average photographer.

The advantages of a larger sensor are that it can cope better with noise at higher sensitivity levels and has a greater dynamic range.

(Credit: Kodak)

Unfortunately in compact cameras, the sensor size doesn't reach anywhere near the full frame specification. Instead, the most common size is 1/2.5-inch, though other compacts do hit larger and smaller measurements on either side.

Compact cameras will mostly have image sensors that produce an image in the 4:3 aspect ratio, which equates to conventional monitor and printing measurements. However, some cameras such as the Panasonic Lumix DMC-LX3 will be able to capture images in different aspect ratios, such as 16:9.

But that's not where the image sensor discussion ends — once you're acquainted with their size there is another element that comes into the equation, and that is their type, which is either CCD or CMOS.

Definition: CCD
Stands for Charge Coupled Device. Most common in compact cameras and are the more mature technology of the two.

Definition: CMOS
Stands for Complementary Metal Oxide Semiconductor. Generally use less power than their CCD counterparts but are often more susceptible to noise.

Only a few compacts on the market use a CMOS sensor, like Ricoh's CX1 and Canon's PowerShot SX1.

 

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