Contents
Introduction
Why buy a digital camera?
Types of camera
Key Features of a digital camera
Image Resolution (megapixels)
Sensor Type
Image Type
Lens Types
Batteries
LCD screen and Viewfinder
Memory
Flash
Video Recording
Manual Settings
Software
Introduction
This article discusses some of the common terms used to describe digital cameras in order to help a potential buyer choose a camera. This article is intended for those who do not already own a digital camera and are trying to make a decision as to which camera to buy.
Why buy a digital camera?
Perhaps the biggest advantage of buying a digital camera over a traditional film camera is that it allows you to view your photos immediately and decide if you want to keep them or if you need to take another picture to get the shot you want. There is no film to get developed and the memory used in the camera is rewritable so there are no recurring film costs and you'll only end up paying to print the pictures you actually want printed rather than paying for the ones that didn't come out properly as well.
Other advantages are that you can usually store a lot more photos on a digital camera than a traditional film camera, it is not uncommon for modern digital cameras to allow the user to store hundreds sometimes even thousands of images on the camera this can be especially helpful if your making a long trip as you don't have to bring hundreds of rolls of film along.The final advantage is that you can easily transfer your images to a PC and email them to friends or place them on a webpage without the need for the cumbersome, time consuming and sometimes quality reducing process of scanning. This can also make it far easier to edit your images to either enhance them or to remove unwanted parts of the image.
Types of camera
Cheap - these cameras tend to take images at a resolution of 640x480 pixels(.35 megapixel) or 320x240 pixels (.064 megapixel), they tend not to feature LCD screens to review images and often power their memory from internal batteries meaning that when the battery is removed all photos are lost. These cameras are really little more than toys and should not be considered by anyone wanting an everyday camera. They can be very good for giving to children or for taking very basic pictures.
Low end - these cameras tend to take images at resolutions between 1.3 megapixels and 5 megapixels and usually feature removable memory, LCD screens and are comparable in size and quality to a typical APS or 35mm film camera. Such cameras will probably suit the needs of most users.
Prosumer - These cameras are a cross between consumer cameras and professional cameras, they often feature resolutions over 3 megapixels, removable memory (and sometimes several types of memory), zoom lenses and tend to be quite large and bulky. These cameras are aimed at the more demanding amateur user, but may not be sufficient for full blown professional photography.
Professional - These cameras are intended for professional photographers and usually offer resolutions over 10 megapixels, removable memory, zoom lenses and SLR lenses and tend to be very large.
Key Features of a digital camera
Image Resolution (megapixels)
All digital images are made up of a grid of dots known as pixels, each pixel actually contains three dots one for red, green and blue. The more pixels which are recorded in a digital image the more detail the image will contain. The number of pixels is sometimes specified in terms of height and width and sometimes as the total number of pixels, as this is usually more than 1 million the term megapixel is used.
Phone and low end cameras are typically under 1 megapixel which can result in low quality images that lack detail, these images will only be suitable for displaying on small screens or as low resolution images on web pages. Most digital cameras and some phones can record between 1.3 and 3 megapixels, such cameras tend to be comparable to an average 35mm or APS camera. Higher end cameras feature more than 3 million pixels and are suitable for large scale prints and professional use.
Megapixels are often used as the key way to define digital cameras', however many other factors can affect the quality of a camera. These might include the quality of the lens, compression levels and flash type. You will often see manufacturers quoting the number of megapixels as the main selling point to a camera, but beware just because one camera has more pixels than another does not automatically make it better.
Interpolation
Many digital cameras make use of a technique known as interpolation, this involves increasing the resolution of the image by simply copying the contents of one pixel into a neighbouring pixel and then blurring the image to remove jagged edges. If for example we have a single red pixel and want to double the resolution of the image then we make this single pixel into 4 pixels and repeat this process across the image. The result is a much larger image, but no new detail will have been added. Having the camera do this is actually of no use whatsoever to you! All that happens is that the image will take up more memory in your camera and if you really want to increase its resolution this can be done very easily using your PC later on. The reason interpolation is used is to make cameras sound better than they really are, it is quite common to see a camera advertised as being ``6 megapixels'' and then to see in the fine print something like ``interpolated resolution, actual resolution 3 megapixels''. The key when buying a camera is to try and find out its actual resolution and to ignore the interpolated resolution. When using a camera its worth only setting it to take images at the actual resolution as this will save you space in the camera's memory and allow you to take more pictures!
Figure: Left is an image taken at resolution of 3 megapixels which is the resolution of the camera's sensor. On the right is a version of the same picture taken using the cameras 6 megapixel mode which is interpolating the image, note how blurry the image is. This extra ``detail'' doubled the size of the image on the camera's memory effectively halving the number of pictures which will fit on the camera's memory card. As can be seen the 6 megapixel version is larger, but it doesn't actually introduce any new detail to the image.
Sensor Type
Digital cameras work by using a sensor which converts different light levels into electrical signals which are then processed by the camera to create an image. There are two main types of sensor CMOS and CCD, explaining the exact differences between these two is beyond the scope of this article. Put simply CMOS sensors are cheap but don't produce great images while CCD sensors are much better but more expensive. All but the very cheapest cameras will use CCD and even some cheap cameras now use CCD. Although some lower resolution phone cameras and many webcams are still using CMOS technology. The key difference in image quality between CCD and CMOS will be seen in nighttime photos, CMOS cameras tend to produce very grainy images and generally have trouble in low light whereas CCDs tend to produce much sharper images with far more detail although they too may still have trouble in the dark.
Image Type
Most digital cameras store their images in a format known as JPEG (Joint Pictures Expert Group), this format compresses the image to reduce the amount of memory space it takes up this compression is achieved through a number of complex techniques which effectively remove detail that human eyes cannot distinguish. A few higher end cameras can take photos in uncompressed formats such as RAW, TIFF and TGA these formats simply store the data data for every pixel in the image recorded by the camera, this results in a slight improvement in image quality over JPEG images but the resulting files are typically 20 or 30 times larger than a JPEG meaning that only 1/20th or 1/30th the number of images can be taken. This feature is generally only of use to professional photographers who are performing lots of editing to the their images or are printing large copies of their images. Most users will be happy with the quality of JPEG images, but if you make large scale prints or photograph very complex scenes may notice some of the side affects of JPEG compression. Most cameras also have the option to vary the level of JPEG compression (often called basic, normal and fine or given as ratios such as 1/30, 1/40 and 1/50), this can be useful when running low on memory space or photographing very simple scenes such as scenes where there is a large amount of sky or a single colour background.
Lens Types
Many digital cameras today offer the ability of a zoom lens, this allows you to zoom in on an area of detail within a scene. This can be very useful as it can allow the removal of unwanted items from the edge of the image and can allow greater detail to be shown. Zoom lenses are normally specified as magnification value beginning with X, for example 2x means you can double the detail of an image. Some cameras also offer the ability to zoom out and take wide-angle pictures which are useful for panoramic views. Virtually all digital cameras also offer something called digital zoom, this simulates the affect of zooming by either taking a higher resolution image, removing the edges and storing a lower resolution image or even by performing this technique with an interpolated image. Be careful when looking at the zoom factors of a camera that it is talking about optical zoom and not digital zoom as digital zoom doesn't actually allow you to see anything more than you could without it whereas optical zoom actually allows you to obtain a more detailed photograph. Cameras with optical zoom functions will usually feature the ability to both automatically or manually focus themselves, this can actually prove to be problematic as auto focus systems can fail to focus properly and can take sometime to focus correctly when they do work. Cameras without optical zoom tend to be fixed focus and thus do not suffer from the problem of needing to adjust their focus, this can be an advantage if you need to take pictures rapidly or in scenes where there is little to focus on such as scenes of calm seas or skys as the camera doesn't need to spend time adjusting its focus.
Most cameras also offer a function called macro mode, this is for when the camera is placed up close to the subject and is useful for photographing documents, photos/paintings, plants, small animals etc. The combination of a zoom lens and macro mode can be particularly useful, the extent of the zoom may be limited when in macro mode. In addition to the ability to zoom in and out, some cameras allow you to attach specialist converters known as tele-photo (which zoom in) and wide-angle (which zoom out) converters in order to extend the zoom functions of the camera. These converters usually clip onto the outside of the camera and require no other functions to operate them. A few higher end cameras known as SLR cameras also feature completely interchangeable lenses which can be swapped in and out to suit the users needs, most digital SLR cameras can use the same lenses as their film based SLR counterparts.
Batteries
The vast majority of digital cameras run on AA or AAA batteries and a few higher end cameras run on special internal batteries which must be charged with the supplied charger in a similar way to a laptop or camcorder. There are advantages and disadvantages to both types, cameras which use AA or AAA batteries usually take fewer photos on a single set of batteries than a camera with an internal battery will take on a single charge. However they offer the advantage of being easy to replace, whereas if you run out of battery using an internal battery and have no spare you are unlikely to be able to recharge your camera without having mains power and a charger available to you. A few very cheap cameras actually use the battery to power their memory which is storing your photos, on such cameras if the battery is removed or goes dead then all photos on the camera are lost.
LCD screen and Viewfinder
Most digital cameras feature an LCD screen on the back of the camera which can be used as a viewfinder, to review pictures after they have been taken and to display settings for the camera. Most cheaper cameras also feature a traditional viewfinder which is simply a lens that the user can look through. Some more expensive cameras actually have a very small LCD display in the viewfinder known as an EVF (Electronic Viewfinder), the advantage of this is that it displays the exact image the camera will take whereas a traditional viewfinder is slightly offset from the main lens and displays a slightly different image, an EVF also allows the camera to display other information in the viewfinder. The main disadvantage of an EVF is that it increases the amount of battery power needed to take a picture and EVF displays tend to be very low resolution making it difficult to see the image which is to be taken properly. A few cheaper digital cameras feature no LCD at all and thus there is no way to see the photo which has just been taken. Such cameras do usually feature a small monochrome display which tells the user how many more pictures the camera can take or which mode it is in, be careful as these displays are often described as LCD displays and some buyers are fooled into buying such cameras thinking they will be able to see the photos they've taken on the screen only to find it just displays a couple of numbers.
Memory
Most digital cameras store photos on a removable memory card, the capacities of these cameras are measured in megabytes in the same way that hard disks and RAM in a PC are. One megabyte refers to the ability to store 1 million bytes, each byte is simply a number between 0 and 255 which can be used to represent any kind of data. Typically digital cameras will get between 2 and 4 images per megabyte (exact figures are usually published in a camera's manual or advertising material) and most cameras tend to include memory cards of between 64 and 256 megabytes. The use of removable cards means you can replace the card when it is full (cards are erasable and rewritable) or upgrade cards to increase capacity. A few cameras do not use such cards and store all photos on internal memory which cannot be upgraded or replaced and some cameras feature both (very useful if you happen to forget your memory card!).
The contents of memory cards can be copied to a PC either by connecting the camera to a PC or by placing the card in a specialist reader attached to a PC. It maybe desirable to use a specialist reader as copying off the camera requires the camera to be turned on and this will drain the camera's batteries 1. Some PCs are now shipping with such card readers built in, it is also possible to read some types of memory card in a laptop PC via a specialist converter and the laptop's PCMCIA slot.
Unfortunately there are several common types of memory card and different camera manufacturers tend to use different types. The table below outlines some of the common card types. It can be useful to choose a camera with a card type that is used by other manufacturers and other portable devices such as PDAs or phones as should you upgrade your camera and have several cards you may want to keep using those cards. Converters do exist to convert some types of cards to others but many of these don't work in digital cameras as they are larger than the card alone and most digital cameras have a small door over the memory card which must be closed in order to take pictures.
Card Type
Dimensions (height, width, thickness
Relative Cost
Capacity
Manufacturers using
Other Notes
Compact Flash
4.3 x 3.6 x 0.5 cm for microdrive and 4.3 x 3.6 x 0.33 cm for compact flash
Cheap
2 megabytes to 8 gigabytes
Most Canon cameras and most high end cameras from other manufacturers. A few smaller manufacturers.
Microdrives are miniature hard disks which are the same size and shape as a compact flash card, but not all compact flash readers can use them.
MMC (multimedia card) and SD (Secure Digital)
3.2x2.4x0.14 cm
Medium
up to 4 gigabytes
Most popular format in digital cameras today. Used by the vast majority of manufacturers.
Secure digital and Multimedia cards are the same size and shape. But Secure Digital offers the ability to encrypt the cards contents, most digital cameras don't make use of this feature and it doesn't matter which type of card you buy.
RS MMC and Mini SD
1.8x2.4x0.14 cm
High
Mainly phone manufacturers.
Physically smaller versions of the MMC and SD card. Used by phones and other small devices as SD and MMC were considered to large.
Smart Media
4.5x3.7x0.08 cm
Medium
up to 128 megabytes
Mainly used in older FujiFilm cameras.
Replaced by the xD card.
xD
2.5x2x.17 cm
Medium
up to 1 gigabyte
Mainly used in newer FujiFilm cameras.
Memory Stick
5x2.1x.28 cm
3.1x2.0x0.16 cm for memory stick duo.
High
Mainly used by Sony devices.
Several variants of the memory stick exist, the most common being the Memory Stick Duo which is being used in a number of camera phones. Very few camera manufacturers other than Sony use Memory Stick for their cameras.
Flash
Most digital cameras will include a flash for shooting at close range in dark conditions. It is common for cameras to offer several different flash modes, these usually include an automatic mode where the amount of light available determines if the flash goes off, a forced mode where the flash always goes off and an anti-red eye mode which makes the flash go off twice in order to reduce the effect of seeing people with red eyes from the flash reflection. Some higher end cameras allow external flashes to be connected, this can be useful if you need a flash brighter than the one included on the camera or if you want to connect the camera to multiple flashes.
Video Recording
Increasingly digital cameras are offering the ability to record short video clips, however the quality of these videos varies dramatically. Most cameras use a system known as Motion JPEG (or MJPEG) to record videos, JPEG is the system used in most cameras to record still images and motion JPEG works simply by recording a sequence of JPEG stills very quickly and storing them in a single file. This is quite a simplistic method and results in very large video files, most digital video systems such as DVD are based on a system known as MPEG which only stores the differences between each frame and results in much smaller files than MJPEG. A few cameras are now starting to use MPEG technology, but these are still quite rare. If your camera does create MJPEG videos then you may wish to obtain software to convert them to other formats such as MPEG. Some cameras are only able to record short video clips as instead of writing the video to the memory card as they record it, they use a small internal memory and then record to the memory card once the internal memory is full. This is done as some cameras can't write to the memory card fast enough to store the video (or the memory card itself isn't fast enough), the result is that many cameras are limited to taking only a few seconds of video at a time even if the memory card can hold more. Even if a camera doesn't have this limit you are likely to find that video recording fills up your memory card very quickly, a typical camera can often fill a 256 megabyte memory card in 4 minutes. An additional limitation on many cameras is that they don't record any sound with the video. There are two key numbers which will normally be given to describe a cameras video functions, these are its frame rate (or FPS) which specifies the number of frames a the camera can record in a given second and the other is its resolution which specifies the number of pixels the video is recorded at. A typical VHS or DVD video is at either 25 or 30 frames per second (depending on if your in Europe or the USA) while many digital cameras only record at 10 or 15 frames per second which results in very jerky video. Video resolution is usually either 160x120, 320x240 or 640x480 pixels, 640x480 is nearing DVD resolution while 320x240 is comparable to a VHS recording and 160x120 is very low quality.
Despite its limitations the ability to record short video clips on a digital camera can be very useful at times, but most digital cameras are not yet at the point where they can replace camcorders and anyone wanting to take large quantities of video should consider buying a camcorder as well. However the quality of video taken by digital cameras is improving and it is likely that over the next few years we will see MPEG video become standard allowing hours rather than minutes of video to fit on a normal memory card. At the opposite end of the scale most camcorders are now introducing the ability to take stills and it is becoming increasingly hard to tell what is a still camera and what is a video camera.
Manual Settings
Most digital cameras offer the user a choice of automatic and manual modes. Under automatic modes all settings are automatically chosen and this will suit most people most of the time. There are times at which the automatic mode makes an incorrect decision or the user may want to override it to obtain a particular effect (such as taking a silhouette or trying to change the way motion appears). The number of options which the user can control vary from camera to camera, the most basic cameras tend to only allow the user to control settings such as the white balance which determines how which can affect the general colour of the image depending on the light. A common problem is that when in low light digital cameras can automatically select a white balance setting for indoor lighting and this can give the image a very blue tint, by manually setting the white balance this can be avoided. Some more advanced cameras allow the user to set other settings such as the shutter speed, this refers to the amount of time the camera's shutter remains open and controls how much light hits the light sensor. This setting can be especially useful at night as shutter times of several seconds can allow the user to take photos over several seconds in order to allow enough light to arrive in the camera for an image to become visible. Another feature commonly found in more expensive cameras is the ability to simulate different film speeds (known as ISO or ASA speeds), these values are intended to correspond to different types of film used in traditional cameras in order to make them easier to understand to people familiar with film cameras. Most digital (and film) cameras will by default operate at 160 or 200 ISO which is fine for everyday daylight/outdoor photography or indoor photography with a flash. Higher end cameras will support speeds of 400 ISO and sometimes even 800 and 1600 ISO, these modes are particularly useful for indoor photography without a flash and this can be useful in museums and old buildings which are poorly lit and do not allow flash photography.
Figure 1: Photo taken using a shutter time of 1/10th of a second and 1/2 of a second. Note how much more detail is visible in the 1/2 second shot.
Figure 2: An example of a similar shot taken on an fairly low end Kodak CX6200 (left) using fully automatic mode (using ISO 200) compared with a high end Fuji S602 (right) using manual mode and ISO 800. Also note how the Kodak image has a blue tint caused by the automatic mode choosing the wrong white balance settings.
Software
Most digital cameras will include a CD with some software on it. This usually includes drivers to allow Windows and sometimes Mac PCs to connect to the camera however most cameras will actually work with Windows XP and Mac OSX without any extra drivers. It is also quite common to find photo editing software supplied on the CD although this software is often in the form of 30 day trials or ``lite'' versions of products which are missing some of the features of their full versions. Some (generally more expensive cameras) will include full versions of the software and even those that supply lite versions may be sufficient for most users. The most popular photo editing program is Adobe Photoshop and this includes some very complex editing features and is often used by professional photo editors, many digital cameras include either trial versions of Photoshop or Photoshop SE (starter edition) a reduced functionality version. Should a camera not include any suitable software don't worry, there are plenty of free programs available on the internet. One such program is known as the GIMP (GNU Image Manipulation Program) and is a free alternative to Photoshop and offers most of the basic and some of the advanced functions of Photoshop.
The average user will probably only end up using a small fraction of the functions offered by most photo editing software. The most commonly used feature will probably be the ability to rotate images so that photos taken when holding the camera vertically can be corrected so that they appear the right way up on the screen. Other common functions include the ability to crop an image so that only part of the image is seen, this can be useful for removing unwanted parts of the image such as peoples heads, cars etc another useful function is the ability to enhance an image to make details which were not visible before appear, it is possible with some cameras to bring out details of images taken in low light so that more detail appears.
Footnotes
...1
A few cameras can actually power themselves off the PC, but most don't.
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