Although Canon describes its newest high-end digital camera as a lightweight, compact SLR, it’s talking in the light of professional cameras. In usual terms, the body is large and very hefty.

The plastic body of the Labs-winning 350D gives way to solid magnesium alloy, bringing the weight of the 5D’s body alone to almost 900g with the battery. Add the kind of lens that will do the sensor justice -- we used a Canon f/4 L 24-70mm in testing -- and you’ve got a camera weighing 2kg or more.

The headline specification of the 5D is the brand-new CMOS image sensor. Not only does this boast 12.8 megapixels, it’s also a full-frame device, being the same size as a 35mm film negative at 36 x 24mm in comparison to the much smaller, roughly APS-sized sensor of most digital SLRs (approximately 25 x 17mm). This immediately puts the 5D in a class of its own, being by far the cheapest full-frame digital SLR on the market at around half the cost of Canon’s own EOS-1Ds Mk II. A larger sensor can resolve more detail as well as tending to produce lower noise, but it’s the primary reason for the 5D’s price tag.

Other specifications are improved over the A-Listed EOS 350D too, although none are major. You do get proper 3.5 percent spot-metering capability, artificially missing from the lower-end Canon digital SLRs, in addition to the standard 8 percent partial spot. Shutter speed extends down to 1/8,000th of a second too, although this is only useful for minimum depth of field in bright conditions for creative purposes. Burst frame rate is still only 3fps -- the same rating as the 350D and slower than the EOS 20D -- although the burst buffer is far larger, with capacity for around 17 RAW frames and 60 JPEGs. In addition, the camera’s ISO sensitivity can be extended up to ISO 3,200. Shots at this sensitivity suffer from the occasional hot pixel and pronounced noise, but the noise is very much akin to chemical film grain and isn’t terribly distracting.

The 5D takes CompactFlash memory, and to get the most out of the camera when shooting in RAW mode you’ll need to make a significant investment in storage. RAW files average around 12MB each, so even a 1GB card will give you only 80 shots -- a 2GB card is the minimum you’ll need for a day of shooting unburdened with worries of full-card messages, especially if you’re taking advantage of the automatic exposure bracketing.

In use, it’s the fantastically large image in the viewfinder that strikes you most. The larger sensor means a larger mirror and a much bigger, clearer preview image, making it far easier to predict how your shots will come out and improving the chances of getting the focus bang-on if you’re doing it manually.

Looking at the results, the 5D excels in its ability to catch the nuance and subtleties of light. The breathing space of the larger sensor seems to make it more sensitive to catching the feel of being there; up the ISO sensitivity in low-light indoor situations and the increased noise levels are easy to ignore against the gorgeous quality of shade the 5D manages to capture, with pretty much the same degree of finesse as film. It isn’t completely cut and dry though. While no-one’s going to sniff at a megapixel rating over the dozen mark, in many instances the absolute need for it is questionable. At lower ISO settings you’ll be hard-pushed to see the improvement in detail reproduction over an 8-megapixel model when printing at standard sizes of A4 and below, but conversely, if you’re a landscape photographer, there still isn’t quite the level of detail that will make you think about moving from a slow 35mm emulsion or medium format.

And there are also areas where the dominance of the 5D isn’t total, relative to its cheaper brethren. We prefer the 350D’s top-mounted on/off switch; it’s far easier to flick on than the lever-like affair mounted almost flush with the back of the 5D’s body. The 350D’s smaller size makes it unobtrusive and easier to keep with you at all times too. Swift operation is easy with the 350D, but try pressing the exposure lock button on the 5D while composing a shot and you could find you need to shift your hand position to support the altered balance of the camera. In addition, it’s impossible for most hands to reach the ISO/drive or AF mode/white-balance buttons one-handed at the same time as turning the adjustment dial. Consequently, it’s a two-step process: you press the button on top and then have six seconds during which you can re-assume a normal grip, rotate either the index-finger dial or rear-mounted rotating wheel to make the adjustment you want, and reframe the shot. It all adds up to the potential for missing photos you might have captured with a leaner device.

Make no mistake -- the 5D is a fantastic camera. However, it isn’t an unqualified success. Many professionals will be drawn toward either the higher resolution or faster burst rates of more expensive models, while enthusiastic amateurs will have to cope with the weight and unwieldy handling of a ‘professionalised’ tool. It’s entirely possible to spend $1300 on Canon’s own 350D, partner it with a decent lens and be just as happy; and your hard disk won’t fill up as quickly either.