Electronic Cameras

A digital electronic camera can be used to acquire still images. Once its memory (RAM) is full, you can transfer your images to a removable storage medium and use it with your computer. Alternatively, you can download the pictures to your machine via a port, usually FireWire or Universal Serial Bus (USB), and then modify the results for use in your own publications.

A Short History of Photography

All cameras are derived from the camera obscura, which was employed by artists for hundreds of years, allowing the outline of a real image to be traced onto a flat surface, therefore making it possible to create paintings with perfectly correct proportions. It consisted of a darkened room with a small hole on one wall that could admit light into the chamber. The rays of light reflected from an object outside the room passed through this hole, thereby creating a small inverted image on the opposite wall.

In later years this simple idea was replicated on a smaller scale as the pinhole camera. Later on, a glass lens was used instead of a hole, increasing the quality of the image and the amount of captured light. However, such developments had to wait for the invention of the daguerrotype, a light sensitive photographic plate on which the image could be stored. This was invented by Louis J M Daguerre in 1839 and soon developed into the first commercial camera.

Early Cameras

In the oldest devices the picture was first brought into focus by using a removable ground glass plate inserted at the rear of the camera. This was then replaced by a photographic plate which was exposed to the light for a given period of time. Unfortunately, an exposure time of 10 to 15 seconds was often required, requiring the subjects of the picture to remain perfectly motionless for the duration.

Older cameras normally used large format plates, typically of 11 by 14 inches, which remained in use by professionals until fairly recently. For example, a view camera, as used in a portrait studio, or a technical camera, would often use two-sided plates of 4 by 5 inches or 8 by 10 inches. In such devices the back and front of the camera could be tilted, allowing corrections to be made to an image, such as reducing the convergence of parallel lines in the image of a tall building.

Cameras for the Masses

By the 1870s glass plates began to give way to gelatine dry plates, and subsequently to flexible film. The Kodak camera of 1888 was the first disposable camera, containing a roll of film sufficient for 100 shots, the whole thing being returned to the factory for developing and reloading. However the greatest development was Eastman’s Kodak Brownie #1, costing $1.00, with film at 10 cents a roll.

Camera mechanisms also became more sophisticated. For example, the optical-coupled range finder, which first appeared in 1916, allowed a photographer to quickly focus a camera by adjusting the lens until a double image in the viewfinder merged into one, while the Ernostar high-speed lens of 1924 provided an aperture of f-2.0, allowing pictures to be taken easily in natural light. And in 1938, the Super Kodak 620 camera introduced automatic exposure (AE) control.

For over 70 years many amateurs used a box camera, which had a single-element lens, limited control of aperture and a fixed-speed shutter. However, some users preferred a folding roll camera, which opened to reveal a lens that could be brought forward on movable bellows and then positioned on its rail so as to set the focus. These devices were very compact, even when designed for a larger film format, were often of a high standard and in some instances incorporated a range finder.

Beyond the Box Camera and Back

The twin-lens reflex (TLR) camera, using a medium film format such as 60 mm by 60 mm, became popular after World War II. This device had two identical lenses coupled together mechanically, the uppermost lens producing the viewing image on a ground glass screen, this being rotated through 90 degrees by a mirror, and the lowermost lens producing the image for the film. Unfortunately, the two lenses suffered from slight differences due to parallax, especially when used for close-ups, although various devices were used to correct the problem.

The modern single-lens reflex (SLR) camera, often employing 35 mm film, uses a single lens, avoiding the complexity of the twin-lens device. It contains a rotating mirror, positioned between the lens and the shutter, which normally reflects the image onto a ground glass screen and on to a pentaprism that provides an eye-level image of correct orientation. When the shutter button is pressed the mirror swings up out of the way, the shutter is actuated and the mirror then swings back.

By the seventies, electronics had created the point-and-shoot camera, which incorporated automatic focusing (AF) or a fixed-focus lens. With this and modern film you didn’t have to worry about setting the exposure or aperture. Instead, you could concentrate on taking pictures.

More recently, the disposable camera has become popular. This is a really a simple box camera made of cardboard, complete with a simple viewfinder, pre-loaded with a roll of film and fitted with a fixed-focus lens suitable for photographing anything over four feet away. Once used, the camera is returned, the film processed and its components used to assemble a new camera.

And, in competing with electronic cameras, the film itself has become more flexible. The most notable development is the Advanced Photo System (APS), which allows prints to be created in various aspect ratios, such as Classic (6 × 4 inches), HDTV (7 × 4 inches, similar in proportions to wide-screen cinema film) and Panoramic (10 × 4 inches, with an aspect similar to Cinemascope pictures).

Flinging the Film

Film was always difficult to handle, even when in the form of a roll. In older cameras it was supplied on a paper-backed spool (which had to be kept out of the light during loading, so as to avoid exposing the edges of the film) but in later designs was housed in a plastic cassette. There were numerous film formats, some already mentioned. Worse still, the film had to be developed before you could see the results. And by that time the opportunity to take more shots had been lost.

The sixties saw the arrival of the instant camera, in which an image could be created in 20 seconds to 4 minutes, without the need to develop film. Instead, a special kind of film was processed inside the camera itself. Once exposed, this was passed between two rollers that released a developing agent over its surface. In the original Polaroid camera, and in Polaroid Professional models, you had to peel the print away from its backing. Later versions, such as the Polaroid SX-70 of 1972, simply ejected a print which developed in normal light, while the SLR model of 1993 conveyed the print to a container at the rear of the camera where you could watch it developing.

The digital camera, which doesn’t require film, has taken a time to be accepted, mainly because early types of charge-coupled device (CCD) gave poor resolution and depth. By the late nineties, however, the results had improved dramatically, and now, in the twenty-first century, it seems possible that the age of film is drawing to a close. Indeed, a modern four megapixel camera (see below) gives a quality approaching that of the high-quality film, but with much greater flexibility.

The Parts of a Camera

In addition to a light-proof box, a camera needs a minimum number of parts for it to work. These include a lens, which focuses the image onto the CCD or film, a focusing mechanism, which positions the lens for the correct focus, a diaphragm, which controls the amount of light entering the camera, a shutter, which permits light into the camera for the required period of time and, last but not least, a viewfinder that allows you to set up the photograph.

These parts are described in more detail in the following sections:-

The Lens

Early cameras have a lens made of one element, a meniscus lens, concave on one side and convex on the other. Although still adequate for a budget camera, such a lens has a very slow speed (it gathers little light) and has other defects. Hence most modern lenses have up to 10 or 12 elements.

The basic performance of a lens is set by its focal length. The following types are used:-

The ability of a lens to gather light is measured by its speed or aperture, also known as its f number. A low f number, such as f/2.0, indicates a fast lens, one that allows in more light. Such lenses are usually more expensive, since they require a high quality of optical design.

The Focusing Mechanism

The image that’s produced by the lens can be focused by moving it backwards or forwards in relation to the film or sensing device. Modern cameras usually have automatic focusing (AF), allowing you to take pictures without the need for manual adjustments. Basically, two systems are used, both of which employ an electrically-powered servo mechanism to adjust the position of the lens:-

The Diaphragm

This device controls the amount of light passing through the camera’s lens. It usually consists of an iris, containing several thin metal plates that are rotated using a lever so as to change the size of the central opening. Reducing the aperture improves the focus, especially at the edges of the image, and also increases the range over which a good focus can be maintained, commonly known as the depth of field. Sadly, it also reduces the amount of light, so you need to hold the shutter open for longer.

The settings for the diaphragm, known as f stops, are often marked on a traditional lens mounting. Standard settings usually include numbers such as 2, 2.8, 4, 5.6, 8, 11, 16 and 22, where a setting of f-2 allows in the most light whilst f-22 gives the smallest opening. Note that each setting doubles the amount of light to the lens, so that, for example, f-8 gives twice as much light as f-11.

Adjusting the Aperture

Although a large aperture setting, such as f-22, captures less light it provides a greater depth of field, meaning that a wide range of distances are kept in focus. A lower setting, such as f-3.5, increases the quantity of light entering the camera but results in a corresponding loss of depth.

In some situations you may want a reduced depth of field, as in a portrait where you require a blurred or ‘soft’ background. The following table shows the effect of using different f stops:-

f StopApertureDepth of FieldBackground
f-2Very largeVery shallowVery soft
f-4MediumModerateSlightly soft
f-5.6MediumModerateSlightly soft
f-8SmallDeeperMostly clear
f-11Very smallDeepSharp
f-16Very smallVery deepVery sharp

You can artificially reduce the depth of field using one or more of the following methods:-

  1. Walking backwards and zooming in the camera.
  2. Moving any background objects further away from the camera.
  3. Using a wide aperture setting, such as f-2.8 or f-4.
  4. Using the Portrait setting on the camera, if available.
  5. Selecting aperture priority mode on the camera, if available.

The Shutter

This mechanical gate controls the amount of time the film or sensor is exposed to light\. The traditional leaf shutter, similar to a diaphragm but driven by a clockwork or electromechanical mechanism, has a maximum speed of 1500 of a second, whilst the modern focal plane shutter uses two moving pieces of rubberised fabric or titanium, accommodating speeds of up to 14000 of a second.

The shutter is normally operated by a button on the camera itself, although this can cause blurring if you accidently move the camera whilst operating it. As an alternative, you can use a cable release, consisting of a remote shutter button on the end of a cable. If you select the bulb setting (older remote mechanisms were operated by a ‘bulb’), often shown as a B on the camera’s controls, you can hold the shutter open for any period of time, thereby accommodating a very long exposure.

Shutter Speed

Although shutter speed is more relevant to a traditional film-based camera, electronic cameras often incorporate some form of adjustment. The value is usually given as a number that represents the fraction of a second used for the speed, such as 1 for 1 second, 250 for 1250 of a second or 4000 for 14000 of a second. A lower number means that the shutter is held open longer, giving a brighter image.

The Viewfinder

This device, essential for positioning your pictures, can consist of a wire frame above the lens and a post at the rear of the camera: the area seen through the frame, with the post centrally positioned, should (in theory, at least) correspond to the area covered by the lens. However, most modern cameras, apart from the TLR or SLR variety, which use their own systems, have either a ‘reverse telescope’ optical viewfinder or a liquid crystal display (LCD) viewfinder.

An optical viewfinder is preferable, since it’s much easier to look at than an LCD screen, although the latter sometimes provides additional information. The LCD viewfinder in professional cameras is often a thin-film transistor (TFT) device, usually between 112 and 312 inches in size.


The picture quality in a conventional camera is usually limited by the optics of the camera itself and the grain size of the actual film. In practice, you can magnify this ‘real’ kind of photograph by a huge amount and still manage to see more detail. Unfortunately, this isn’t true of a digital image where the quality is set by the number of pixels in the camera, commonly known as its resolution. So, if ‘blow up’ a digital picture you don’t see more detail, just bigger pixels. As a rule of thumb, with a medium-resolution camera, you shouldn’t expand an image to more than about five inches by seven.

In order to obtain a reasonable aspect ratio, more pixels are usually used in the horizontal direction than in the vertical. Typical resolutions are shown below:-

320 × 240Standard resolution (VGA)
493 × 373 
512 × 360 
512 × 480 
640 × 480 High resolution (SVGA)
756 × 504 
768 × 576 
800 × 600High resolution (SVGA)
850 × 984 
1016 × 1528 
1024 × 768High resolution (XGA)
1152 × 864 
1280 × 9601.2 megapixels
1280 × 1000 
1280 × 1024 
1600 × 1200 
1792 × 1200 
1800 × 12002.0 megapixels
2048 × 1536 
2160 × 14403.1 megapixels
2272 × 17043.87 megapixels
2272 × 17123.89 megapixels
2288 × 17123.92 megapixels
2304 × 17123.94 megapixels
2400 × 18004.3 megapixels
2544 × 19044.8 megapixels
2560 × 19204.9 megapixels
2592 × 19445.0 megapixels
3026 × 20186.11 megapixels
3256 × 24487.97 megapixels
3264 × 24487.99 megapixels

When choosing a camera you should check that the resolution given is its true optical resolution. Some cameras employ software interpolation to improve the subjective quality. However, even though the final image looks smoother, the actual clarity of the picture isn’t improved by this process.

Megapixel (Mp) Ratings

The total number of pixels used in a camera is obtained by multiplying the horizontal and vertical resolution. For example, a device with a resolution of 1280 × 960 has 1.2 million pixels. This means it can be called a 1.2 megapixel camera, or just a ‘megapixel’ camera. Although this sounds impressive, the results are invariably inferior to those produced by conventional film.

Unfortunately, some camera makers give a megapixel rating that includes those pixels at the very edge of the camera’s sensor, even though these can’t form part of the image. This is partly due to the fact that the sensor is square, although the image produced by the lens is circular, as shown below:-

Manufacturers, in their enthusiasm for marketing, have exploited this phenomena. This means that a camera described as a 3.3 megapixel device may only have an ‘active’ area of around 3.1 megapixels.

Matching Resolution to Output

The resolution of your chosen camera must be sufficient for your final product. Fortunately, images used on the Web only need to be at screen resolution, meaning that a low-cost camera of restricted resolution is perfectly adequate. On the other hand, if you’re creating pictures for high-resolution colour printing, possibly with image resizing, you’ll need something much more extravagant.

For standard high-quality printing, usually produced at 300 dots per inch (dpi), you’ll need a camera with a rating of around 3.2 megapixels. In theory, this is only adequate for pictures up to 6.8 by 5.1 inches. Luckily for the wallet, perfectly reasonable results can be obtained when printing on a full sheet of A4 paper. However, for regular production of such pictures (or even larger) you should consider a camera with an optical resolution of 2272 × 1704 or higher.

Resolution and Data

Higher resolution images require a greater amount of memory (RAM) in the camera and more space in other storage media. For example, a typical low-cost camera may hold 72 standard resolution images but this number can fall to 36 or less if you take high resolution pictures.

A digital camera can store images in one of several formats. The standard JPEG document is very convenient since it’s easily handled by any QuickTime-based application. Other formats such as FlashPix, iVue or TIFF can also be encountered, sometimes with JPEG compression, as well as RAW image files that can take up less space than standard TIFF documents.

The following table gives a rough guide to the number of pictures that can be stored in various sizes of RAM or storage media, although, as already mentioned, this can vary according to the file format.

▼ Resolution▼ File Size (MB)16 MB32 MB64 MB128 MB256 MB512 MB1 GB2 GB
1 Mp0.44080160320640128025605120
2 Mp0.917357114228456811372275
3 Mp1.21326531062134268531706
4 Mp2.081632641282565121024
5 Mp2.56122551102204409819
6 Mp3.2510204080160320640
8 Mp3.549183673146292585

  Special Features

Electronic cameras often have similar characteristics to a traditional film-based device. However, they frequently come with extra capabilities that modern technology can provide. One example is red-eye reduction, a mechanism that provides a degree of ‘pre-flash’ illumination prior to the main flash, allowing the human eye to respond and giving the subjects of your photographs a rather less ghoulish appearance.

You should take particular care to consider the camera’s type of storage medium (see below). If you use the right kind of camera you can avoid adding extra hardware to your computer. And if you want to download images to your machine you should choose a camera with a compatible connection. The most common interfaces, in order of preference, are FireWire, USB, SCSI or a serial port. Once again, by carefully selecting a camera you can avoid the need for extra hardware.

Optical and Digital Zoom

Most cameras provide a means of zooming-in on a subject. Better models employ optical-zoom, as found in traditional cameras, which ensures that the entire image sensor is always used, thereby maintaining its full resolution. The maximum zoom varies according to the camera: typically, it’s between 2x and 6x.

Unfortunately, cheaper devices often incorporate digital zoom, which usually restricts the information to the centre of the sensor. This seriously limits the resolution, even when interpolation is used to smooth out the pixels. A typical camera provides a digital zoom of up to 10x.

Cameras that incorporate both digital and optical zoom are often accompanied by misleading specifications. For example, a model with 3x optical zoom and 10x digital zoom is often advertised as having a total zoom capacity of 30x, even though the digital feature may be almost useless.

Automatic Focus and Exposure

Most modern cameras come with automatic focus (AF) control and automatic exposure (AE) control. Although both of these can be useful, you should check before buying a camera to see which of these features can be manually overridden and the range of adjustment.

The Flash Lamp

A flash is essential for indoor shots, although forcing it to operate, whatever the light levels, can also be useful, since it can reduce problems associated with uneven lighting, even in daylight. However, the range of a flash is limited to around 8 feet, which means that you’ll need to use other methods to avoid indoor pictures that have pitch-black backgrounds. Here are some suggested settings:-

Speed: 100    Aperture: f-5.6    Shutter: 1/155

In addition, the flash should be forced to operate and red-eye reduction should be turned off. If these settings aren’t possible you could try night time mode or slow synchro mode, often indicated by the ‘stars over a mountain’ icon.

Automatic White Balance

Most people are unaware that the colour spectrum reflected from objects varies with lighting. For example, a picture taken under incandescent lamps can seem too warm, with a prominence of reds and yellows, whilst a shot taken outdoors can seem cold, with an excessive amount of blue or green. Technically, this problem involves white balance, which is related to colour temperature. The latter is measured as an absolute temperature in kelvin (K). For example, the temperature of daylight at noon is around 5,500 K, indoor lighting is at 3,200 K and the light at sunrise is at 1,800 K.

Traditionally, white balance is fixed by placing a filter in front of the camera lens. Most digital cameras, however, have inbuilt correction, known as automatic white balance (AWB). The controls for AWB usually have four icons:-

Camera Light SettingEquivalent Filter
SunSunlightSky 1A
CloudCloudy or Flashlight81B warming
BulbIncandescent Lamps80A cooling
BarFluorescent LampsFLD fluorescent correction

Adjustable Film Speed

Traditional film comes in different speeds or sensitivity, the faster varieties being the most sensitive to light and the slower versions usually giving the best picture quality. Film speed is normally specified according to ASA or ISO ratings, typically set at 100, 200 or 400 for conventional film.

Although digital cameras don’t actually use film, most models have an adjustment that allows them to behave as if they did. The sensitivity of such cameras can be varied over a wide range, such as 120 to 200, 125 to 800 or 50 to 400, although some go as high as 1600, or even 6400.

  Storage Media

Most cameras use a removable storage medium for transferring images to your computer, usually in the form of a card. These solid-state removable devices don’t contain any moving parts, making them highly reliable and robust. Instead, they employ a kind of random-access memory (RAM), often in the form of flash RAM, which is similar to the RAM found in computers and other digital devices. Unfortunately, this method of data storage is more expensive than traditional disk drives.

The effective capacity of such media varies according to the required image quality. For example, a standard 10 MB card can accommodates five medium-resolution images, increasing to 43 pictures with compression and rising to figure of around 200 for low-resolution compressed images.

Various types of card are used, most of which are incompatible with each other. These include CompactFlash (CF), Memory Stick Pro, Memory Stick Duo, MultiMedia Card (MMC), Secure Data Multimedia (SD/M) and xD-Picture Card. There’s little to choose between these, and what you end up with is usually determined by the slot (or slots) in your camera.

Disk-based Storage

Some cameras use traditional disks for data storage, although this is fairly uncommon. The following devices may be encountered:-

Click drive

This miniature removable 40 MB hard disk format is rarely used. A stand-alone Click drive can be connected via the USB port to your computer or you can plug a specially-designed drive into the PC Card slot provided many portable computers.

Floppy Disk

Although cheap and used in some Sony cameras, floppy disks are completely inadequate for very high quality images or for any computer that doesn’t have a matching drive. A typical camera uses JPEG compression to squeeze 25 ‘fine’ images or 50 ‘normal’ images onto a single diskette.

IBM MicroDrive

This is a very small disk drive that can be inserted into a standard CompactFlash Type II slot. Several sizes are available, including 170 MB, 340 MB and 1 GB.

  Downloading via a Port

Some cameras don’t accommodate any removable storage media and only have the RAM that’s built into the camera itself. This means you must rely on downloading images via a computer port.

The time taken for a download is dependent on the resolution of the pictures and the speed of the interface. The amount of information sent can be huge, especially for high-resolution images. This means that you should always use the fastest possible port, preferably FireWire if your machine supports it. Failing this, you can use USB, SCSI (you’ll need an extra card in a modern machine), or a serial port on a older machine. Unfortunately, downloading via a serial port is very slow.


1997 Grolier Multimedia Encyclopedia, © 1997, Grolier Inc.

MacWorld magazine (UK), IDG Communications, 2001-4

©Ray White 2006.