In some respects digital cameras are built, and work, in much the same way as film cameras, and consist basically of a light-tight box with an optical lens fitted to it. Light passes through the lens mechanism, which focuses the image, and when the shutter is open, strikes some sensitive material which records the image produced. The technologies used to focus the lens - manual or auto-focus - and to determine the correct exposure - metering - are also generally the same. 

With film cameras, it is of course the film that is the recording medium, and when it is developed produces images from which prints can be made, if negative film has been used, or projected if slide film is involved. The film also acts as the means of image storage, so each type does the jobs. It records the image, stores it, and is its means of transfer to print or projection.

It is here that a digital camera differs radically from a film one, as it carries out these jobs separately, and by electronic means rather than chemically. The recording medium is an electronic silicon chip, known as a sensor. This measures the light hitting it, computes it, and then passes it to the camera for further processing, so all it does is record the image. When the camera receives information from the sensor, it processes it, according to how it has been programmed, both by its makers and the individual using it, and then 'saves' [writes] it to memory in the form of an file. These files are known as 'image files', and the memory to which they are saved is usually in the form of a removable 'memory card'. Some cameras, usually cheaper ones, use internal memory, rather than external. There are also some that use both. Once the image has been written to a file in memory, it can then be viewed on the LCD screen that most digital cameras have on the back. This is but one of the many advantages a digital camera has over film, but is probably the most widely known. Once an image is recorded to a memory card it can be printed or viewed straight from it, or transferred to a computer's hard drive, either to be altered in some way - called image manipulation - or for more permanent storage, say on CD/DVD.

So a digital image file can be considered as being the equivalent of both print and slide film since it can be used to produce a print of the image, or just to view it on a screen of some kind at a range of sizes. And if a digital projector is used, be projected at a large size on a projection screen or wall, in much the same way that a slide film image can.

Early digital cameras were first made by electronic companies. They were big and bulky and the designs had little in common with  film cameras, with some novel and weird looking cameras being produced. As they developed and the technology behind them improved, camera companies also began to make them. Now almost all companies involved with cameras make digital types, and the style, size and design of  digital cameras has begun to mirror that of  their past film cousins. In certain cases some companies have film and digital products that it is difficult, at first glance, to tell apart, although today the range of film cameras still made is now very small and digital cameras are the main type produced. Such is the pace of change that most camera makers have abandoned film camera production, and now only make digital cameras, whilst others have ceased to exist or have been taken over by electronic firms such as Sony. This was the fate that befell Konica-Minolta.

At present, digital cameras fall into two main categories, in much the same way that film one's do, Digital compact - Digicams, and Digital SLR - DSLR. There are also now Digital Medium Format cameras, and there are digital 'backs'. These can be fitted to many of the Medium format film cameras made in the past which have interchangeable film backs.

Generally, digital cameras are referred to not only by their type but by their sensor size, i.e. how much detail they can 'capture' in an image. This is a reflection of the size, in pixels, [2mp, 3mp etc] of their imaging sensor, not its physical size, which also differs amongst cameras, and has an equal if not greater bearing on image quality. Basically the more pixels a sensor has, and the larger it is, the better the image quality, and the larger an image can be printed and give a good quality print. However the downside is that the larger a sensor is physically, the larger the camera is that houses it, which is why DSLR's are so much bigger than digicams.

These are two main digital camera types that the average person will encounter

                                        Digicam                                                           DSLR

Apart from cost and size, there are a number of  features which separate them, giving each type distinct advantages and disadvantages over the other. In order to understand and fully appreciate what each has to offer, it is best to explain the different way each type works.

Digicam.

Below is a very basic diagram of a digicam. As you can see, when you look through the optical viewfinder most cameras of this type have, you do not get the same view as the camera's lens sends to the sensor. In general use this is okay, but it can cause some trouble when taking a shot close up, due to parallax distortions. You can't frame the shot correctly and you might not get the picture that you expect. 

However, because this is a digicam there is another way of viewing the shot you wish to take, and this by using the LCD screen on the back. Most digicams automatically switch on the LCD when their macro mode is chosen as this is the only way of seeing what it is that the camera will take a shot of in this mode. But the rear screen can be used at any time for viewing the scene. This is known as pre-viewing, as opposed to re-viewing, which can be done once a shot has been taken.

Pre-viewing shots on the LCD is useful because in most cases the screen will show the shot as it will be after it is taken, with white balance and any other effects you have chosen, applied to it. Not only that, but what you see is what the lens sees, because the image on the LCD comes from the camera's sensor, so in effect you get the TTL viewing [Through The Lens] that has previously been the sole preserve of SLR's. This is because of the basic design of digicams, and is something that it has not been possible  until recently, to do with DSLR's.

It's made possible because, unlike film cameras and Digital SLR's, a digicams shutter is not closed, but remains open all the time, and only shuts down to the correct aperture to take a picture. This has a disadvantage as well however, in that it takes longer to take a shot when you press the shutter button because of the extra sequences the digicam has to go through before the shutter can work. This is known as 'Shutter lag' and is the time taken between pressing the shutter button and the shutter 'firing', that is opening and closing, thus taking the shot.

Another drawback with pre-viewing using the LCD screen is that it becomes difficult to see the screen in bright or sunny conditions. This has led to an increasing number of cameras that have an Electronic Viewfinder [EVF] instead of an optical one. This is a miniature LCD screen and shows all that appears on the full size one. The downside is that the resolution is low, so its difficult to judge if focus is accurate, and like the full size LCD, it consumes a lot of battery power. But it means that you can view a shot just as you would using a SLR, with TTL viewing, but with the added advantage of the chosen effects applied.

Digital SLR.

Here is a basic diagram of a SLR. You will see that unlike a digicam, when you look through the viewfinder you see through the lens (TTL). This is achieved using a mirror mechanism, known as a reflex mirror, (which is where the SLR title [Single Lens Reflex] came from), and a prism.

A Digital SLR works in exactly the same way as a film SLR, in that when you press the shutter button to take a shot, the mirror flips upwards out of the way, the shutter opens and closes, and then the mirror falls back down into place. Because the mirror's normal position is down - so you can see through the viewfinder - it means the path to the sensor is blocked. So unlike a digicam, the shutter stays shut as in a normal film camera, and no pre-viewing of the shot using the LCD is possible. The LCD screen on a Digital SLR is used purely for re-viewing shots already taken,

The advantage of this is when you look through the viewfinder the resolution you see is what your eye is capable of seeing, and thus it is easy to see how the shot looks in terms of whether it is focused correctly, is sharp, and includes all that you want to capture in the shot. One benefit of this is that no power is used, as its all done optically, whilst another is that the shutter lag is minimal, and is generally un-noticed in comparison to a digicam. 

Although SLR's have traditionally used a glass prism known as a penta-prism to produce the view seen through the viewfinder some recent DSLR's have been fitted with cheaper to produce penta-mirror systems instead where mirrored surfaces similar to the reflex mirror are used. These are also lighter, helping to keep camera weight down. The only downside is that the view produced is often not of the same quality as that through a penta-prism being duller, i.e. less bright and of lower contrast.

A new specification to arrive with some of the latest DSLR's is a feature called 'live-view' mode which operates in much the same way as using a digicams rear LCD. ( Please refer to  Live View  for details)

Camera Options

One of the main benefits of a digital camera is the number of options that are available to the user. Once you get used to these they become second nature and you can easily forget how restrictive a film camera is in comparison. You can, on an individual shot by shot basis if you wish, alter the ISO rating, the white balance, take Black&White instead of colour, and numerous other settings which vary from camera to camera. Perhaps just being able to alter the ISO speed, or take as many shots as you want, and be able to view or print them without 'finishing off' a roll of film are the most liberating. Another is the 'macro' mode most have that enables you to take close up or magnified shots of small subjects. Then of course there's the small matter of being able, seconds after you've taken a shot, to review it on the LCD screen and re-take it if its not to your liking. And even with most cameras of being able to use that rear LCD screen to view and compose a shot before taking it.

Lets take a look at the some of the basic options, not found on film cameras, that are common to digital.

• Sensitivity/ISO.   A sensor can be set to different levels of sensitivity, to suit changing light levels, and the standard is to follow film practice with sensitivities that match that of film. So the ISO standard is used, and just as you might pick either a 100/200/400 speed film etc, so you can set the sensor to do the same. The range of settings will vary. A digicam may have a choice of say 2 or 3, starting at perhaps ISO50 or ISO100. Generally DSLR's have wider ranges with some covering 50-3200. You can change this setting for every shot taken, should you wish, a distinct advantage over film. The ability to use higher ISO's to overcome slow shutter speeds, and thus camera shake and blurred shots is a distinct advantage, although it does come at the expense of lower image quality through higher noise levels, a side effect of digital camera sensor design, which is roughly the same as using higher ISO speed film. Images have lower contrast - less 'punchy' - and look 'grainy'. This is relative to the ISO sensitivity used, as with film.

• White Balance.   The colour of light varies according to how bright it is. Generally the correct light colours occur at midday in average conditions. In the morning the colour has a colder 'blue' tone, and in the late afternoon a warmer 'red' tone. These are called 'colour casts'. If you take a shot under artificial light then a colour cast will also often be evident, and can range from sepia (creamy brown) under tungsten lights to blue in very bright conditions using flash. With a digital camera you can overcome this using 'white balance', which attempts to correct for any cast and produce a shot with the right colours. All cameras do this automatically using Automatic White Balance (AWB). However AWB can only work reliably within a certain range of the correct mid-point and in extreme lighting conditions can fail. This is most often seen in low light level shots under artificial lights. So many cameras also have a range of pre-set WB settings. Some also offer manual WB where you can set your own to suit particular situations.

• File formats.    All digital cameras save the images they take using the JPEG file compression format, a universally known and used graphic image computer file format, and offer a range of compression settings to enable the files to be reduced in size to save space on a memory card. Some cameras also offer other file formats where quality is of paramount importance and these are TIFF, where no compression is applied, and RAW where no effects are applied in camera and the image file must be processed later using a computer. Both these latter formats can result in very large files which can take the camera offering them a considerable time to process, and require very large capacity memory cards to store.

• Quality.   This refers to the amount of compression applied to files saved in the JPEG format. 3 settings is the norm, usually set as 'Best', 'Better, 'Good', or Superfine, Fine, Standard, with Best/Superfine being the least compressed. Sometimes a star rating is used instead with the more stars the lower the compression ratio used. The amount of compression is usually 1/3rd, 1/6th and 1/12th of the nominal sensor size respectively, so for a 6mp camera the JPEG file size would average, 2mb, 1mb, and 1/2mb respectively. The actual levels of compression however, vary from camera to camera depending on the image quality the manufacturer wishes the camera to produce, and the shot being taken, as some have more detail than others. The lower the compression the higher the image file that results. All cameras show how many shots can be taken on the memory card being used at the settings chosen, and many re-compute this as each image is taken.

• Sharpness/Contrast/Saturation.   These are effects applied by the camera during the  processing of images taken and many cameras offer the ability to adjust these to suit the individuals taste. Usually a number of settings will be available either side of the ones set to default, +/- 2 is common.

There are also some features that are only found on Digital Compact cameras, which we refer to as Digicams on these pages, and these are:-

• Macro mode.   Most digicams offer this to enable you to take close-up shots of small objects, so they fill the frame. The way this works, and the level of magnification possible, varies depending on the camera used. Taking the above Pentax 33L as an example, macro mode is available across its entire focal range and as close as 10cm, a 2p coin filling the frame.

• Movie Mode.   There are many that also offer this feature although you should not expect to get camcorder quality. The resolution is often low, and the movies take up a lot of space on a memory card, but can be useful on the odd occasion. The latest digicams do offer higher resolution video, some at camcorder size, but the quality still can't match the still image output they can produce.

• Black & White/Filters etc.   As well as colour it is often possible to shoot in black & white or apply various 'effects' filters, although some of these are rather gimmicky and of little real value.

• Panoramic mode.  Software is available that will allow you to take several adjacent shots and then 'stitch' them together to make a panoramic picture. Some cameras can help you take the series of shots and then 'stitch' them together to make the panoramic picture, either 'in camera' or afterwards using supplied software. 

In more recent times digital cameras of all types have been provided with an increasing range of 'options' which can be chosen and set in addition to those listed above. In the vast majority of cases it is now seen as normal to have them. In the main the number and type of options varies between cameras and depends to a large extent on the type of digital camera involved.

One trait that has become quite common however, is the need to use the rear LCD screen and the camera menu that appears on it to set most options, the number of 'hard buttons' used to set camera options being reduced to the absolute minimum in some cases. This is not a problem for little used and accessed options but can be for commonly changed ones such as metering, AF, ISO etc. and can materially affect how quick and easy a camera is to use. Constant use of the rear LCD is also a considerable drain on batteries.

What You Need.

In order to use a digital camera you really need just two things, batteries and a memory card. Usually, and depending on the camera you buy, these are supplied along with it. Sometimes these are only just enough to get you started, and extra batteries and more/larger capacity memory cards are needed for worthwhile use of the camera. However, in order to then be able to do anything useful with the images you have taken, store them somewhere and print them, extra items are required and it is here that a computer comes to the fore.

Usually you will receive with a camera, software to enable you to connect the camera to a computer, so that the images you take can be downloaded to it, stored, viewed, adjusted if needed, and then printed via an inkjet printer. Many cameras can also be connected to TV's so slideshows of the images on the memory card in the camera can be shown. You can also show slideshows on the computer and write the image files and slideshows to CD/DVD. There is no need to produce prints to view the shots you have taken, and so no cost, apart from batteries, is involved in taking images using a digital camera. Only when you wish to makes prints from them.

There has been of late, a concerted effort on the part of makers of cameras and inkjet printers to make digital cameras 'computer independent'. A whole host of products have arrived that you can use to download and store images on, as well as inkjet printers that will take memory cards direct, but the upshot is that these products can cost as much if not more than a computer, without the versatility that comes with owning one. 

One of the main advantages of using a digital camera is the flexibility it gives to you. Most buyers of digital cameras also own computers, and most of the advantages of a digital camera are obtained by using them in conjunction with one. And despite claims to the contrary, a basic computer is all you need. Along with a basic inkjet printer if you want prints. Obviously a better computer will allow you to work faster, and the better the printer, then the better the print it will make, but the choice is yours.

If you feel that you don't have the time or experience to produce lots of prints you now have the choice of using the many High Street outlets that will take your memory card or CD of images and print them out for you. 

 More details on the various subjects mentioned here can be found by following the links on the