How To Buy a Digital Camera

Digital Cameras Are Not All the Same, from Sensor Size and Pixel Count to Exposure Control

Most of us have taken a photograph at some time during our lives. Some of us have taken many thousands of pictures, but getting a good picture depends on a number of factors, not the least of which is having a camera with us at the time. In choosing a new camera, for most of us the choice is no longer which film camera to buy, but rather which digital camera to buy. It may not even be primarily a camera; many mobile phones and small palm-top computers are capable of good results. The days of a camera on a mobile phone capturing only a basic image with a pixel count under 1 million have long gone. So how can you compare digital cameras in order to decide which one to buy for yourself? Let's explore the factors that influence how a digital camera responds and provides us with an image.

  1. Pixel count – sensor size. Each light-sensitive spot on the image sensor (a photo-site) has dimension – length x width. And all these photo-sites make up a grid, which forms the stored image from light focused on the sensor by the optical system (the lens). Not only do the number of these photo-sites matter, but the physical size and the distance between neighboring photo-sites makes a difference too. In the cheaper ranges cameras, detailed specifications of this nature are rare to find.
  2. Exposure control. Expect this to be an automatic function with little or no manual override allowed. The amount of light reflected by the scene in view makes the image recordable, either on film or a digital sensor. If the variation between the bright and dark areas is too large, the system finds it more difficult or impossible to cope. The sensitive surface can only cope with a limited range of image reflectance (contrast). If contrast is too high, the camera or the photographer must override the normal exposure settings (the amount of light allowed to fall on the sensitive surface to record the image) so that the contrast range is compressed into a range that the system can handle.
  3. Flash. Photographers have to use whatever light is available to record an image, from bright sunlight to night-time shots. Modern cameras usually have a small flash system built in to provide extra light in dark outdoor or indoor conditions. The flash may also fire to lower the contrast found in bright harsh sunlight, adding some fill light to the shadows. Flash tends to be limited in range – so people or subjects more than 3-5 meters (9-16 feet) apart are likely to be very dark in any case. These built-in flash units are intended for indoor domestic use.
  4. Viewfinder or framing system/view screen. The classic solution was an optical viewfinder indicating what will be included in the picture field. Objects outside the viewfinder should not appear. Modern digital cameras have a small LCD (Liquid Crystal Display) view screen to preview and review photos. Using some clever electronics, the view seen by the lens is shown on the screen, and when the button is pressed, the image is 'frozen' and captured or recorded. LCD screens are notoriously difficult to see in bright sunlight. You may have to estimate what will be in the field of view as you press the shutter button to take your masterpiece. One further option is to have an electronic viewfinder system, which has the advantages of optical finders with few of the disadvantages of direct vision systems.
  5. Digital picture storage and file download. The camera is synonymous with film, a silver sensitive optical recording system in use for over 150 years in various evolutions. The digital camera stores a computer readable file of digital, numeric data on a media chip or card in the camera body. Cards are now available in some 7 or 8 different types and variants, and you can only use the appropriate card in a digital camera. Once the picture is captured most users will download the images to a computer for storage, editing, or printing. Some offer a choice of connecting the camera directly to the computer, reading image files from the media card into the computer using a card reader, or moving some images so they can be sent or taken to the local photo-print store to get conventional photographs printed.
  6. Battery life. All this electronic capture system needs power and energy to operate or it fails. If you don't have spare batteries with you, expect to have to stop taking pics when the battery runs low and you then have to swap to a fresh battery, recharge the main cells, or if all else fails – stop taking photos.
  7. Other features.
    • Image stabilization (IS)– Desirable, but unlikely to be fitted on low- to medium-price cameras. Holding a camera with arms outstretched to the front viewing on screen is prone to induce camera shake, the main reason for unsharp photographs.
    • Tripod bush/fitting – Desirable if you want to capture images of landscapes and city-scapes without using flash. Found on more expensive models only – same logic as having IS. Only useful if you have a tripod!
    • External flash control/trigger – The small flash, sometimes a pop-up style, has many limitations starting with low power output, and is aligned close to the optical axis of the lens, thereby making 'red-eye' flash results highly likely.
    • Save images in JPEG and RAW format simultaneously – The optimum picture quality is stored in the file of numbers from the image sensor. To save space in memory or on media cards the manufacturers follow a standard compression formula optimized and specified by the Joint Photographic Experts Group, JPEG (.jpg). This file compression discards some image data, but makes better use of available storage.

      For the best quality, use RAW format, a one-to-one file capture from the photo-sites on the image sensor. This sometimes needs special software to enable editing on your computer. More expensive models may provide dual-save, making RAW and JPEG files of the same photo available for whatever purpose you need. Look out for JPEG 2000, the latest development in JPEG compression algorithms.
    • Zoom (optical and digital) – The lens captures a specific field of view, variable from wide to narrow if it's a zoom. It may not be wide enough or narrow (long) enough. Optical zoom of the lens is unlikely to be more than x5, and more commonly will be x3. This means an object in the picture will appear 3 times closer or five times closer. Digital zoom may produce impressive figures (e.g. x10 or x20), but the enlargement is obtained by throwing the outer pixels away and re-sizing the image based on the central pixels left. You can do this with any computer photo editing program anyway, and you can also do this when asking for prints from your local store.
  8. Cost. Digital cameras have been on sale for over 15 years and they can now produce pictures almost indistinguishable from a conventional silver print at regular print (EN Print) sizes. Spending upwards of $150 will buy a basic, good digital camera, and you never need buy another film as long as you have it. It is equally possible to spend thousands of dollars on the latest top-end cameras with a lens from makers such as Canon, Nikon, and Leica, and with a number of other reputable makers not that far behind.
  9. The lens as a factor in making your decision. You generally get what you pay for. When buying a straightforward digital camera, my only comment is that the lens is probably fine. My personal preference is for a compact design and to save battery power; I opt for a lens with a folder optical path, as this does not have to be telescoped out from the camera body. The folded optical path may be less than ideal, but I find that I use a camera of this design more than my other cameras. The lens quality is great.
In conclusion, there are few limitations to buying and using any digital camera. Logic appears to suggest you need to spend at least $150-$200 at present, but this limit may drop over time. A phone with a built-in camera can be a realistic alternative if you choose your gadget wisely.


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Nice comprehensive article. I've read quite a few how-to's on digicams, and none of them recommend the incredibly obvious: test drive test drive test drive. Get your buns to a real camera store (not Best Buy or it's ilk, but to Ritz or Wolf. Use Google and type "camera store + city or town" to get a list). The trained salespersons in those stores are happy to become your quick tutor. And, you may even buy what they recommend because everyone is competitive these days.

My nickel's worth...

By Murry Shohat

Hi Mary
A very fair comment, but as on-chip sensor arrays have improved, lower prices and more sensor sites, the mobilephone camera is more and more popular, and the results are often more than adequate. But, my main reason for making this point is that a camera is only useful if you have it with you - and I know I don't carry my camera everywhere - but I do regularly have my cell phone with me!

By Rik Whittaker

Hi Rik,
I still don't buy things with multiple functions as they often don't do anything that well..i.e. telephone that is a camera, a voice recorder and an MP player as well...anyway, your tips are very practical and sensible.

By Mary Norton

Hi Ae
A camera with built-in protection above and beyond the normal will cost more and may only be useful if you are likely to subject your camera to harsh environments.
My preference for this was to keep the camera cool and in a separate plastic bag only taking the camera out when taking a photo.
An old timers trick for taking shots in rain was to cover the camera body with a clear plastic bag, fixed in place round the lens so the optical path was clear using a rubber band. It would be essential to prevent condensation building up if in hot humid conditions.
The worry may stop you getting photos, so unless you want to spend lots of 'dosh' on highly protected cameras I guess the best option for many would be a cheap disposable film camera - probably giving as good a photo as you will get from many digital models but being limited to 36 exposures and having to wait for film to be processed.

By Rik Whittaker

thanks for the info. buyers might also want to consider water proof, shock roof, or ready-for-printing features - depending on their needs. i sure would like to know which camera is the best when going to the beach.

By Anonymous