Outdoor Photography. Chiz Dakin

of this title Jon was fairly sceptical about digital cameras – and with good reason at the time. But things changed pretty rapidly within the next few years. Quality went up, prices came down, and digital rapidly became mainstream. Today we feel fully justified in assuming that the vast majority of our readers use digital cameras.

      Cameras

      The sensor

      The heart of every digital camera is the sensor, the image-forming chip which has taken the place of film. If you believe the hype, all that really matters about a sensor is how many megapixels it has. This is rubbish. Most digital cameras today have more pixels than you need, and there’s a strong argument that some have too many.

      But first, what is a pixel anyway? The word is short (sort of) for ‘picture element’. In essence it’s a coloured dot. Blow up any digital photo big enough on your computer screen and you can see the individual dots of which it’s made. In a 6-megapixel camera, for example, there are (approximately) six million of these individual dots, in an (approximately) 3000 × 2000 pixel array.

      Sunset over hills behind Garden Cove, Campbell Island, Sub-Antarctic New Zealand (Chiz) Bigger pixels are better at holding detail from deep shadows and bright highlights

      Lyth Valley, Cumbria (Jon) It’s much easier to build wide-angle lenses for larger sensors – and without a wide-angle lens (24mm) this dramatic sky would have been lost

      The camera’s processor has to read, record, and subsequently reassemble data from each and every one of these pixel-sites. Actually it has to do even more than that. The individual pixels in almost all cameras only record data of one colour. If you could enlarge an image straight from the sensor, you would see it’s made up of red, green and blue dots of varying brightness. Recompiling these into a genuine full-colour image is a complex process called demosaicing.

      For each shot the camera has a lot of number-crunching to do before it can save a JPEG image file to the memory card. If that number-crunching power doesn’t keep pace, then adding more pixels will make a camera slower.

      There’s another, even more basic, reason why the mere number of pixels is not the only issue. If you have two sensors of the same physical size, one with six megapixels and one with 12, it’s obvious that the individual pixel-sites on the 12mp sensor are going to be smaller; each will only have half the area, which means it can only collect half as much light. This may not matter too much when there’s loads of light around, but that’s not always certain in the great outdoors.

      This indicates that we should be less obsessed with pixel numbers and more concerned with pixel size. Pixel size is determined by the number of pixels and the size of the sensor. However, while the pixel number is plastered all over advertising and packaging, you’ll usually have to dig deeper for any information on sensor size.

      So here it is in a nutshell:

       SLR-type camera: big sensor

       Compact camera: small sensor

       Mobile phone camera: teeny tiny sensor.

      There are variations within each category – for more information, see under ‘camera types’, below – but very crudely, SLR sensors are somewhere in the postage-stamp size bracket. Compact camera sensors are smaller than your smallest fingernail. And cameraphone sensors are so small you can barely see them.

      Even an HD TV screen is only equivalent to about a two (yes, two) megapixel image. So exactly who needs 14 or 16 megapixels?

      To coin a phrase, you can’t change the laws of physics. There are physical limits, set by the wavelength of light among other factors, which mean pixels can’t go on indefinitely getting smaller and smaller. Cameraphones are close to the limit already. Ultimately, the only way to add more pixels will be to use a bigger sensor.

      Alternatively, a bigger sensor allows the use of bigger pixels. Because bigger pixels grab more light they perform much better in lower light levels. This means less need to use flash, which is usually a good thing. But bigger pixels also produce cleaner, less noisy, images at all light levels. They’re also better at holding detail from deep shadows and bright highlights – something else which is often an issue in outdoor photography.

      Of course bigger pixels require bigger sensors, which in turn means bigger cameras and bigger lenses. As far as outdoor enthusiasts are concerned, this is unfortunate. No-one wants to carry extra weight and bulk on the hills. However, there is an extra factor: larger sensors make it much easier to build wide-angle lenses, which are great for all sorts of shots. There’s more on lenses below.

      The image

      Large or small, the sensor is not the only factor determining the quality of the final image. Digital images go through a complex series of processes before you can actually view them, even on the camera’s own screen. This is especially true of those images which are recorded by the camera as JPEG files (extension .jpg).

      The advantage of JPEGs is that they land on the camera’s memory card in a ready-to-use form. You can print them or upload to sites like Flickr right away. But this advantage can also be a disadvantage. Because the image has already been processed by the camera, there’s a lot less room for manoeuvre if you want to do more to it later. You can open it on your computer and make it lighter or darker, make the colours warmer or cooler, and so on, but the fact is that a lot of the original data has already been discarded, leaving a lot less to play with.

      A few cameras still offer the option to record files as TIFF format, but there’s rarely anything to be gained by it and they take up a lot more memory card space than JPEGs.

      Converting them to TIFFs on the computer later could be a good idea, but that’s another story – see Chapter 12.

      If you do like working on your photos on the computer, or if you’re concerned to get the best possible results even (or especially) from tricky shots, then many cameras offer an alternative, known as shooting RAW.

      RAW is a generic term arising from the fact that these image files record the raw data from the camera’s sensor. It’s not an acronym and there’s no clear reason why it’s become customary to write it in capitals. Each camera maker has its own RAW format with its own file label: Nikon’s is .NEF and Canon’s is .CR2 or .CRW, for example.

      Seppo in kayak, Doubtful Sound, New Zealand (Chiz) Portrait mode keeps colours slightly muted, and doesn’t sharpen the image too much

      RAW files require further processing on the computer before you can do anything useful with them. This doesn’t mean that you have to spend ages picking over each image individually, as processing can be semi-automated, but it does mean that you need suitable software.

      For more about software, see Chapter 12; the key point now is that the choice between shooting JPEG for convenience or RAW for ultimate quality and flexibility is a very important one.

      It might seem obvious that you’ll shoot JPEG for an easy life, but it’s not that simple. If you shoot RAW, then getting camera settings right is important. If you shoot JPEG, then getting camera settings right is absolutely vital. And this doesn’t just apply to basic exposure settings. JPEG processing deals with a lot more than whether the image is too light or too dark. It also locks in values such as colour balance and colour saturation. Yes, you can alter these afterwards, but within much tighter limits.

      Let’s take one quick example. Many cameras have a Portrait mode. This will set a fairly small aperture to limit depth of field and concentrate attention on the subject, and shooting RAW or JPEG will make no difference whatsoever to depth of field. However, Portrait mode also