Outdoor Photography. Chiz Dakin

stands for Single-Lens Reflex. Digital SLR is often shortened to DSLR. An SLR is built around a mirror, which diverts the image from the lens into the viewfinder during viewing. The characteristic bulge on top is a pentaprism, which is necessary so you can see the image right-way round and right-side up.

      The Nikon D3100, a typical contemporary ‘entry-level’ digital SLR (Jon)

      When you take a shot the mirror flips up out of the way before the shutter opens to expose the sensor (or film) and capture the image.

      It can even be argued that the gap between compact and SLR is wider in the digital age than ever before. A 35mm compact used the same film as an SLR, but digital SLRs have much bigger sensors than most compacts. As we’ve already suggested, this is a very significant difference.

      However, not all SLRs are equal in the sensor size stakes, as the table below shows. The majority of current DSLRs have APS-C (DX) size sensors. These are slightly under half the area of a ‘full-frame’ (FX or FF) sensor, which is the same size as a frame of 35mm film. If the number of pixels is the same, then each pixel on the FX sensor is also twice the size and has twice the light-collecting power. FX size cameras are best for low-light or high-ISO shooting – which can be great for action – and they also give the widest view from any given focal length of lens. However, they are bigger, heavier and (nearly always) more expensive.

      At the other end of the scale, the Four Thirds size sensor has little more than a quarter of the area of FX, but it’s still nearly ten times larger than a typical compact camera sensor. Most manufacturers seem to view the DX format as the best compromise for most users, but Four Thirds systems are certainly worth considering where weight and bulk are really critical. There’s actually not that much difference in the weight of camera bodies, but Four Thirds systems can use smaller and lighter lenses. The main manufacturer of Four Thirds SLRs is Olympus. The only manufacturer to use the Foveon sensor is Sigma.

      Let’s briefly revisit the five key points we identified when looking at compact cameras:

       RAW Shooting Always an option on DSLR.

       Lens range Interchangeable lenses mean a huge range of focal lengths is available. Crucially, SLRs (especially FX format) can give a wider view than any of the other classes.

       Sensor size See table above.

       Speed of response Varies, but even lesser SLRs are better than most compacts.

       Viewfinder An SLR would not be an SLR without a viewfinder, and it will nearly always be better than any compact. Most SLRs now have the option of Live View on the rear screen as well, which makes handling more awkward in most situations but can be handy when shooting at ground level, overhead, or on a tripod. Some SLRs have a fold-out rear screen, which can be an advantage for Live View or movie shooting but is basically a fragile nuisance the rest of the time.

      SLR variants

      The SLR is a brilliant design, but that doesn’t mean there’s no room for improvement. An obvious weakness is that big mirror at the heart of the camera. Every time this flips up it creates noise and vibration. And because the mirror needs room to flip up and down, there’s a large void in the middle of every SLR. This makes cameras bulkier than they would otherwise need to be, and pushes the lens further away from the sensor, which limits some of the options available to lens designers.

      Recently – in 2009 to be precise – we saw the first camera that could be described as an SLR without a mirror. Instead it has an electronic viewfinder which takes its data directly from the imaging sensor. Electronic viewfinders used to be dreadful, but – just like camera-back screens – they’ve improved enormously. They aren’t yet as sharp or as immediate as an SLR finder but they are still getting better.

      As yet the photographic world can’t quite agree what to call these cameras. We rather like Electronic Viewfinder – Interchangeable Lens, which creates the acronym EVIL. However, it hasn’t yet stuck. You’ll also see them called ‘compact system cameras’ or ‘interchangeable lens cameras’. As SLRs are also interchangeable lens cameras, this is not a helpful term.

      Whenever we use the term ‘system camera’ in this book, we are including both conventional SLRs and the variants covered in this section.

      The Olympus PEN E-PL1, one of the new generation of compact system cameras (Photo courtesy of Olympus)

      Panasonic and Olympus produce models using a Four Thirds size sensor. Panasonic’s cameras look more like traditional SLRs, with a viewfinder bulge on top, but are noticeably slimmer from front to back. Olympus’s PEN series are more compact-like and rely solely on the screen image for viewing, unless you splash out on a separate attachable viewfinder.

      Sony’s NEX series cameras use APS-C size sensors – the same as the majority of DSLRs – but in a slim, compact-like body. The large sensor, as we know, has many advantages, but it does mean that lenses can’t be dramatically smaller than regular DSLR lenses. Viewing is screen-only.

      All these cameras promise SLR-like quality and lens choice in a smaller, lighter package. This sounds like a good combination for the outdoor enthusiast, but it’s still early days for this whole class of camera. They definitely merit consideration, but they also demand a thorough, hands-on trial before you splash the cash. This is especially true of models with no viewfinder; even if you’re used to screen viewing on a compact, it’s a different ballgame with the larger, heavier lenses that these cameras use. Using one hand to support underneath the lens is essential, for a start. Also, their continuous Live View means that they will make heavier demands on batteries than a conventional SLR.

      Sony have yet another trick up their sleeve with their SLT (Single Lens Translucent) cameras. These look reassuringly similar to a conventional SLR but have a fixed, translucent mirror inside. This allows most of the light to pass through but reflects around 30% up to an array of focus-detection sensors. This means that, unlike any other SLR or ‘EVIL’ camera, there’s no interruption to focusing from mirror or shutter action. This appears to offer obvious advantages for tracking rapid action in particular. On most cameras focusing in Live View (and when shooting movies) is relatively slow; not on an SLT.

      The SLT viewfinder looks superficially like an SLR, but it is electronic. The cameras are slightly smaller and lighter than comparable SLRs, but the absence of a moving mirror makes them quieter, less prone to camera shake and potentially faster. They retain all the other handling advantages of an SLR and should be much better with long lenses than the ‘EVIL’ type. We can’t help thinking that this technology could be what most of the world’s news and sports photographers, in particular, will be using in a few years time. However, it’s not clear, at this early stage, whether SLT cameras totally live up to the promise.

      CAMERAS: WHAT NEXT?

      Well, here’s the thing. All of these innovations have been rolled out by manufacturers with a relatively small share of the SLR market. Sony may have come from nowhere to third place in this market in a few short years, but the two big beasts – especially in the professional sector – are still Canon and Nikon. And so far, both of the giants have remained resolutely committed to the conventional SLR format. However, it would be extremely surprising if their R&D departments weren’t working on new technologies.

      Camera Setup

      Image quality and size

      ‘Image quality’ principally refers to the RAW/JPEG choice, which we’ve already looked at in some detail. As we’ve seen, this is a pretty basic decision.

      If you shoot JPEG there are usually a couple of extra options: these may be buried in menus but should not be overlooked. Quality settings such as Fine, Normal or Basic refer to the degree of compression applied to the images. More compression