Slightly better cameras in the three to five megapixel range usually also have more controls for focusing and image adjustment. Prosumer models are designed for those who are serious about photography but don't have the budget for professional equipment. Professional digital cameras offer the greatest flexibility for capturing digital images. These cameras are the most expensive and can cost several thousand dollars.

You are presented with many choices when buying a digital camera. There are different types of image sensors, storage cards, batteries, as well as extra features like video and audio recording. As mentioned in the previous article, image sensors and lenses are the most important parts of a digital camera for capturing quality images. They are not the only things to consider, though.
 

Controls

Many of the controls on digital cameras are accessed through a menu system. An easy-to-use menu system is a great benefit to any digital photographer, so this is an important point to consider when shopping around. The menu system should be clearly laid out so that you can access settings such as resolution, flash, and exposure settings. Too many buttons can be confusing and can inhibit the average user from accessing all the features.

Exposure Settings

Exposure settings allow you to adjust the camera for various types of light. Almost all digital cameras have an automatic mode which will do the adjusting for you, but better cameras will give you more control over aperture settings and exposure times. These can give your photos a more professional look, but some people may not be interested in this level of control.

Video and Audio

Many digital cameras allow you to shoot videos and/or record sound. These features can be handy, but the amount of video that can be captured is quite small compared to a dedicated camcorder.

LCD Display

LCD displays allow you to see pictures you have taken. This is essential for deciding which shots to keep and which to discard. The display may also function as a viewfinder allowing you to see how your shot will look before you press the shutter button. Some of the cheapest digital cameras do not have an LCD display.

Software

Some cameras come bundled with image-editing software like Adobe Photoshop Elements or Ulead PhotoImpact. Software is a great way to edit your photos before they are printed. Software packages can cost up to $100 if bought separately so having it included with the camera is a serious buying consideration.

Try Before You Buy

If possible, take a few pictures with a digital camera before you buy it. This will give you a feel for the controls and the ease of use. How does the camera feel? Is it solid or does it seem like a plastic toy? Is the LCD screen easy to view under various lighting conditions? Giving the camera a tryout will answer these questions.

There are lots of reasons for that popularity. Digital photographs are incredibly versatile. You can send them to friends and family by email, post them on a web site, transfer them to CD, store them on your computer, and use them for slide shows which can be viewed on your TV or computer monitor. They can of course be printed, and not just as traditional 4×6 pictures. They can be used to make personalized calendars, greeting cards, and even be printed on objects like coffee mugs and t-shirts.

For many people, the biggest advantage of digital photography is that it eliminates the need for picture processing. No more trips to the photo store – pictures can be viewed almost instantly on the display screen of the camera. Since there is no developing, digital photography doesn't need dangerous chemicals that could end up in our water supplies.

Another big advantage of digital photos is the ease with which they can be edited. Computer software allows digital images to be altered in any way imaginable. They can be cropped, the colours can be changed or enhanced, the contrast can be adjusted, imperfections can be removed, and images can be combined to create startling new designs. All this can be accomplished in a few seconds with just a few key strokes or mouse clicks.

Using a digital camera is the best way to take advantage of all the features of digital photography, but you can also use a traditional film camera and convert your negatives to the digital domain. If you are uncertain about whether or not to take the digital plunge, converting negatives allows you to get a taste of the wonders of digital photography without investing in new equipment. Most photo developing stores offer this service.

Digital cameras, however, offer so much more than film cameras. They have a viewing screen which functions as both a view finder and a picture viewer. This means you can preview pictures you've taken just seconds before. If you don't like it just delete it, or if there is a section that is good, crop it before saving it back to the camera's memory. Many digital cameras also function as simple video recorders that can capture video along with sound – anywhere, anytime.

All this must come at a hefty price tag, though – right? Wrong! Digital photography is becoming more affordable every year, and the technology to make fabulous photos is well within the reach of the average consumer. Add in the money you'll save in development costs and you have an affordable, practical, solution for all your photography needs.

Blurring is especially noticeable in photographs taken with extended exposures (under low-light conditions, for example) and becomes more apparent when photographs are enlarged. Even slight motions of the camera can cause blurring.

Supporting the camera can help to reduce camera movement. A tripod provides the best support, but cameras can also be stabilized with objects such as doorframes or tree trunks. Monopods are suitable for outdoor use when tripods are either too heavy or too cumbersome to set up.

There are hundreds of tripods to choose from in a broad range of prices. The most expensive ones are made of composite materials such as carbon fiber which is lighter and more durable than either aluminum or alloy. Expensive tripods are usually equipped with quick release mechanisms for adjusting the legs and the camera mount.

Each tripod has three heights which must be considered — maximum, minimum, and collapsed. For most purposes, the maximum height should allow you to use the camera at a comfortable standing position. You rarely need a tripod higher than this. If you do a lot of close-up work, the minimum height is an important measurement, although extensions can be added to the head which allow the camera to be brought close to the base of the tripod. Finally, the collapsed height is important to determine the tripod's portability — compact tripods are usually easier to carry around.

Tripods usually have a center column to attach the tripod head. This center column can be used for fine height adjustment and some models allow the camera to be tilted down towards the ground for closeup work. Look for a center column with a hook – these can be used to hang heavy objects for increased stability.

Tripod heads are the part of the tripod that the camera attaches to. They allow the camera to swivel and move up and down. This movement is accomplished with two basic types of head – the three-way pan tilt head, and the ball head.

Traditional heads are the three-way pan tilt type. They have three different axes and each is controlled with its own mechanism and lock. The locking mechanisms make this type of head ideal for situations where precise control of the visual field is needed, but can be inconvenient for other uses.

Ball heads allow all three axes to be set at the same time, so they are easier to use. They are also more expensive but most photographers gladly accept the higher price for the increased flexibility in camera movement.

Monopods are an ideal alternative to tripods where portability is a concern. They consist of a single support which the camera is mounted on. Outdoor photographers often prefer monopods over tripods because the latter are bulky and difficult to set up.

Using a monopod is almost as easy as pointing and shooting. The monopod gives the camera the extra stability necessary for good quality shots.

Carrying a tripod is easier with a case or a carrying strap. Cases can be used to hold all your camera equipment but are bulky to carry around. If you don't have a lot of equipment a shoulder strap is the best solution for carrying the tripod.

If the camera needs to be perfectly level, small bubble levels can be attached to the tripod. Some tripods come equipped with levels, but they are also available as inexpensive accessories.

Batteries are used to power the flash and the LCD display. Leaving the display on more than necessary is a surefire way to drain your batteries, and if you don't have a spare set on hand, that once-in-a-lifetime photo can be lost.

Most digital cameras use AA batteries. These are available almost anywhere in the world and relatively inexpensive. Using nonrechargeable batteries, however, is uneconomical in the long run as well as being bad for the environment. It is much better to have several sets of rechargeable batteries on hand.

Digital cameras are 'high drain' electronic devices which mean they require batteries which have a comparatively high energy level over their energy cycle. The best type of rechargeable batteries for digital cameras is NiMH (Nickel-Metal Hydride). These relatively inexpensive batteries will keep your camera operating longer than any other standard type of battery. NiMH batteries are made from non-toxic materials so they are environmentally friendly.

Some manufacturers supply lithium-ion batteries for their digital cameras. They are more expensive than NiMH batteries but hold their charge almost twice as long. They also don't lose their charge while in storage the way that NiMH batteries do, and their power drains at a predictable rate so that it is easy to gauge how much power is left.

Alkaline batteries are not suitable for digital cameras. You can always use them if nothing else is available, but their power will be used up after just a few shots. Rechargeable alkaline batteries are even worse — they may only be good for two or three shots.

A set of fully charged NiMH batteries may give you up to 100 shots if you are careful with power consumption. This number will be reduced if you use the flash a lot, leave the monitor on between shots, and do a lot of zooming and focusing.

Battery Chargers

Battery chargers come in a variety of models – be sure to get one that is rated for the type of batteries you are using for your digital camera. Some chargers can handle both NiMH and NiCad batteries but if these chargers are not set up properly they can damage the batteries by overcharging them.

Lithium-ion battery chargers are usually provided by the camera manufacturer. They may come as part of the digital camera package or be available as an accessory.

Batteries have to be charged together as a set. If your digital camera uses four AA batteries you need a charger that can handle that number. Similarly if your camera uses two or three batteries — the charger must be compatible.

Some of the inexpensive battery chargers keep on charging the batteries for a fixed length of time. This can be bad for the batteries because they can be overcharged. Look for a battery charger that has a micro processor which controls the charging cycle. This type of charger switches off automatically when the batteries reach their maximum charge.

Each f-number allows twice as much light to enter the camera as the previous f-number. For example, f/8 produces an exposure which is twice as bright as f/16.

Aperture settings have two basic effects — the amount of light which strikes the image sensor, and the 'depth of field'. Depth of field refers to the length of the image which is in focus. Large aperture settings have a shallow depth of field — this means that the focus of an image is relatively short which causes foreground and background objects to appear out of focus. Small apertures have a deep depth of field — almost all the objects (foreground and background) will remain in focus.

Aperture is directly related to shutter speed for determining the amount of light that enters a camera. Large apertures combined with fast shutter speeds let in the same amount of light as small apertures combined with slow shutter speeds. Determining which combination is best for a particular situation requires photographic judgment that comes with experience.

To make it easier, most cameras have an automatic setting which will do the calculations for you. Many photographers, however, wish to control aperture and shutter speed for artistic effect.

Since a large aperture can be used in conjunction with a fast shutter speed, this is often a good combination for action shots because the fast shutter speed will 'freeze' the motion with a minimum of blurring. Large apertures can also be used for low light conditions where there is very little movement in the scene. In this situation you would combine the large aperture with a slow shutter speed.

Simple point-and-shoot cameras usually have a fixed aperture, and it is only with more expensive models that you have adjustable aperture settings. When choosing a digital camera, one consideration should be the aperture range. There are several ways this can be expressed in the camera specifications: maximum aperture, aperture range, maximum wide-angle and maximum telephoto apertures.

It is more useful to know the aperture range of a particular camera rather than the maximum apertures. A larger range gives you more flexibility in the kinds of shots you can take. A good range for all-purpose photography is from f/1.8 to f/16.

Each lens has its own aperture rating. Telephoto lenses typically have a shallower aperture range than wide-angle lenses because longer lenses need proportionally more light. This is because they are gathering light from a smaller source, so larger apertures are needed to produce f-numbers which are consistent with shorter lenses.

Although modern digital Single Lens Reflex (SLR) cameras usually have a mechanical shutter, electronics can achieve the same effect by clearing the image sensor and then allowing the sensor to gather light for the required time. This type of 'shutter' is used on less expensive cameras.

Many digital cameras have an automatic setting to determine the appropriate shutter speed or it may be set manually for greater artistic control.

Shutter speed is always calculated in relation to 'aperture' – the size of the opening of the lens. These two settings are used in conjunction to control the amount of light that hits the image sensor.

Fast shutter speeds are used to 'freeze' action. Longer shutter speeds can be used in low light conditions and to allow moving objects to blur. This effect is often used when photographing running water.

Since a fast shutter speed lets in less light than a long shutter speed, it is usually combined with a larger aperture setting to allow sufficient light to reach the image sensor. Similarly, long shutter speeds are combined with small apertures.

Shutter speeds are measured in fractions of a second in an approximate 2:1 scale starting with 1 second. The scale runs 1 second, 1/2 second, 1/4 second etc. down to the fastest speed of 1/8000 second. In addition, many cameras have a 'B' shutter setting (the shutter stays open as long as the button is pushed) and a 'T' setting (the shutter stays open until the button is pushed again).

Aperture settings are also measured on the same 2:1 scale. This allows for the same light exposure by increasing shutter speed one notch while opening the aperture one notch. Light conditions for a given scene allow for a range of shutter speed/aperture combinations. There is no 'correct' combination – it depends on what kind of effect the photographer hopes to capture.

For example, if you wish to photograph a moving subject such as an athlete during a sports competition, you would normally use a fast shutter speed to freeze the action. This fast speed must be used with the correct aperture to expose the image correctly.

A slower shutter speed, however, could be used if you pan the camera to match the movement of the athlete. This can create a more dynamic effect as parts of the picture (especially the background) will be blurred. Slower shutter speeds must be compensated for with smaller aperture settings.

Another common photographic effect is controlling the depth of field to highlight the subject. Large apertures have a smaller depth of field which means that the foreground and background will be (pleasingly) out of focus. To achieve this effect you must combine the large aperture setting with a fast shutter speed.

Flash adds another dimension to the aperture/shutter speed equation. Interesting effects can be achieved by using flash to freeze the main motion while allowing some of the action to be blurred with a slower shutter speed.

Traditional photography uses film which must be developed in a darkroom using various chemicals. The developing process produces 'negatives' which must be printed before you can see the picture. Digital photography uses an electronic sensor to capture the image. The sensor is made up of millions of individual 'pixels' (picture elements) which convert light into a number. Rather than waiting for the picture to be developed, digital pictures can be seen almost instantaneously on the viewfinder of the digital camera.

The quality of a digital photograph depends a lot on how many pixels it has. The number of pixels is sometimes referred to as the 'resolution' of an image, and can be expressed as a dimension (800 x 600), or the number of pixels per inch. A common resolution for computer screens is 800 x 600 and this means the monitor can display 800 pixels from side to side and 600 pixels from top to bottom for a total of 480,000. Digital photography commonly uses much higher resolutions than computer screens with resolutions in the millions of pixels (megapixels). A camera with a resolution of 2048 x 1536 has a total resolution of 3.1 megapixels.

As mentioned above, each pixel is represented by a number. The size of that number determines the colours scale that can be represented. For example, black-and-white pictures can be represented with pixels which are just eight bits in length. If you are familiar with binary arithmetic, you know that an 8-bit number can represent decimal numbers from 0 to 256. Black-and-white photographs, therefore, can have a total of 255 shades of gray as well as black (0) and white (256).

Colour must be represented with larger numbers. 16 bits per pixel, for example, is necessary to have a colour scale of 65,536 different shades. 24 bits per pixel can represent more than 16 million different colours. Most digital cameras use 24 bits per pixel, but some professional equipment has a colour resolution of up to 48 bits per pixel for more than 280 billion different shades.

There are several factors that affect the quality of a digital camera, but pixel resolution is usually seen as the most important. Choosing an adequate pixel resolution depends a lot on the size of the photographs you want to print. Keep in mind that the number of pixels in an image does not change, so pictures with larger dimensions will have fewer pixels per inch which results in a loss of detail if the picture size becomes too big.

Photo labs usually print pictures at 300 pixels per inch, so using this as a standard measurement you can calculate how many megapixels your camera should have. The maximum print from a two megapixel camera at 300 pixels per inch is 5.8" x 3.8" — less than the standard 4" x 6". A camera with four megapixels can print pictures to a maximum size of 8.2" x 5.4" at 300 pixels per inch.

Of course, there is nothing to stop you from printing larger pictures. Pictures printed at 200 pixels per inch are slightly less sharp but still quite acceptable for many purposes. At this resolution, you can get pictures up to 8.7" x 5.8" from a two megapixel camera, and 12.2" x 8.2" from a four megapixel camera.

Spam is unsolicited e-mail – often with some alleged commercial purpose, but almost always unwelcome. It's sent in bulk by automated programs to millions of e-mail addresses, usually offering products and services such as prescription medicines, get-rich-quick schemes and pornography.

As much as the objectionable content, it's the method of sending spam that upsets most people. Unlike junk (snail) mail that's delivered by the Postal Service at the expense of the sender, the cost of sending spam lies almost entirely on the receiver and the transmitters. There is a cost to the sender, when they use paid services to distribute, but the charge is often minimal.

So, why is spam so hated? After all, it can be eliminated with a simple delete. While receiving one or two unwanted e-mails a day is a minor inconvenience, when the number rises to 10, 20, or a hundred per day it becomes a major problem.

Before e-mail became an accepted means of communication, spam was mostly limited to USENET – newsgroups established to discuss specific topics. As it advanced, mechanisms for cross-posting – sending one message across multiple groups – came widely into use.

The ability to cross-post was, regrettably, quickly exploited by spammers. The same message could be sent to thousands of newsgroups with no regard for their actual interests.

With the rise in popularity of e-mail, spammers gained a whole new arena in which to inflict harm. They use software (spambots) to collect e-mail addresses posted on web sites or newsgroups, and send out their unwanted messages to millions of recipients at once.

Spambots are programs used to harvest e-mails for subsequent compiling into lists in order to – you guessed it – spam large groups of individuals in one easy and ill-bred way.

The sheer number of messages sent makes spam profitable. This is known as 'shotgun' advertising – when it's advertising at all and not a scam. Most reputable advertisers use 'targeted' marketing, which involves soliciting e-mail addresses voluntarily – or at least attempting to analyze the recipient – to send only messages that are likely to be welcomed.

Most people won't fall for get-rich-quick schemes or be interested in random merchandise solicitations, but if even one recipient out of a million provides his or her credit card number, the spammer's efforts can be amply repaid.

But don't despair. Spam is being fought on several fronts simultaneously. Companies and trade groups, legislation and technology are combining forces to make spam a thing of the past.

The effort may never be 100% effective since one man's spam is sometimes another's welcomed offer for a hotly sought item. But large strides are being made in all three areas.

In the interim, an individual needn't wait passively for others to solve the problem. We look at some tips on how to reduce spam and hinder spambots in later articles.

THE ENEMY – Crackers and Hackers

Geeks make a distinction between crackers, who break into systems to do damage, and hackers who enjoy taking programs apart just to see how they tick. We'll stick with the more common, though less accurate, term of hacker. (The term 'hacker' originally meant 'someone who makes furniture' with an axe. Crude, but effective – like most computer viruses.)

Viruses are actually a particular type of computer 'malware' – a general term covering all types of malicious software. The most common types are viruses, worms and Trojan horses.

VIRUSES

A virus is usually hidden inside another program such as an installation program delivered via e-mail attachment. (Biological viruses require a host organism to live and reproduce, hence the name.) When the 'host' program is run, the virus program also runs. Once it's in memory the virus is able to do its dirty work, which usually includes infecting other programs.

After the infection stage of the virus, there's a destructive stage. The virus waits for a pre-determined trigger (such as a specific date or a certain number of times the virus has replicated itself) before delivering its 'payload'. Payloads range from simple messages to file deletion commands to destruction of the core operating system.

When first developed, computer viruses were commonly distributed on floppy disks. With the growth of the Internet downloaded files and e-mail are the preferred delivery mechanisms. E-mail can contain attachments which can be any kind of computer file. Any executable file can be infected with a virus, and shouldn't be run unless you're confident they're virus free.

WORMS

Worms are similar to viruses in that they're self-replicating. They reproduce themselves across networks without human assistance, such as e-mail sending. A worm, though, doesn't need another executable program to be distributed.

Worms usually affect networks more than individual computers on the network. Their self-replicating behavior can overload network resources, causing slowdowns in data transmission by consuming massive bandwidth normally used to forward normal traffic. Network systems that route Internet traffic are just specialized computer hardware and software. They, too, can be affected by malware.

Worms can also be designed to carry a payload, using a 'backdoor' installation program. A backdoor is a hidden access point to a computer that bypasses the normal login procedure. They're commonly used by spammers to distribute junk e-mail, for example.

TROJAN HORSES

Trojan horses are the third common type of malware. A 'trojan' is a program that pretends to do one thing but actually does something different. (The term comes from the story of the Greeks who built a large wooden horse in which to hide. Their enemies, the Trojans persuaded they'd receive a gift, took the horse inside their compound giving the Greeks easy access to wreak havoc.) Unlike viruses or worms, a Trojan doesn't replicate itself.

Trojans may be hidden in otherwise useful software. Once started they can do almost anything including erasing data, corrupting files, installing backdoors and logging keystrokes so that hackers can steal information such as credit card numbers and passwords.

FIGHTING MALWARE

Elsewhere in the series, we'll discuss what is and can be done to combat the spread of malware. In the interim, just remember not to be passive and expect the problem to be solved by others. Fighting viruses requires active participation from vendors, webmasters AND users.

Adware

Adware actually has two flavors – software supported with advertising, or a more malicious sort. The first could be a useful utility released free of charge but using advertising to generate revenue to support development – similar to TV commercials. You're not required to watch, but if you do you get ads along with content. Often this type of software is also available in ad-free form for a modest price.

The other, more malicious, type monitors your browsing habits and delivers targeted advertising. This type of software may be considered a type of spyware, especially if it's installed without your knowledge and consent. When does adware becomes spyware? A gray area. Some software vendors claim that disclosing the inclusion of this type of software in the user agreement grants legal consent for its installation. Most users, obviously, don't read the fine print, which is full of legal jargon and unattractively formatted.
 

Spyware

Spyware can have a more insidious meaning, however. This can refer to software which does much more than simply monitor a user's browsing habits. It can also redirect your browser to advertising sites.

This type is almost always installed without the user's consent or knowledge. It may be hidden in another program or arrive as the payload of a worm or virus. It's also illegal in many countries. In the U.S. the FTC (Federal Trade Commission) has indicted, and in some cases convicted, several purveyors.

Some software vendors require the user to install spyware as part of a package. File sharing utilities like Kazaa or BearShare are notorious for this practice. Its inclusion is declared in the user agreement but users don't have the option of not installing it – if they want the main program they have to install the spyware as well. Annoying, but legal.

The spyware installed with these, and many other, programs gather information about web browsing habits so that targeted advertising can be delivered to the user. 'Targeted' advertising is designed to be presented to specific groups, selected by analyzing their buying or browsing habits. Selections are made by discovering gender, age, frequently visited sites or by other criteria.

Spyware vendors argue that it doesn't collect specific personal information and there's an active controversy over whether it constitutes legitimate market analysis or privacy violation.

Most users find it annoying at best and intrusive in the main. Advertisers claim it's the best way to deliver products and services to potential new customers who may actually end up wanting what's offered. Legally, they assert, it's just another form of free speech. Users retort that the advertisers' free speech doesn't reach to their browser or e-mail Inbox.

The argument isn't likely to be settled soon.