How many pixels are enough? That's the question that's most often asked by photographers contemplating the purchase of a digital camera. And can you ever have too many?

While resolution is an issue of considerable interest to amateurs, for professionals it can be a matter of success or failure. Photography is an increasingly competitive business, and if your rivals can produce better quality images, they're more likely to get the job than you - it's as simple as that.

This is less of an issue in wedding and portrait work, where many customers seem happy with the results they get from six to eight megapixel cameras, but when it comes to advertising and stock photography the ultimate file size can be extremely important.

Many professionals make sales through picture libraries as a way of supplementing the income they earn from commissioned work. But over the last couple of years stock agencies have become more demanding and discriminating when it comes to accepting images that have been captured digitally. Most, such as Alamy (www.alamy.com), for example, now insist that files be 48Mb and over without interpolation.

It may be a remarkable coincidence, but the ultimate file size you get from the Mark II version of Canon's EOS 1Ds is 47.5Mb, which is within a whisker of that magic figure. This means that for an investment of £6,000 - not an outrageous sum when you consider that a single image could easily return that in a year - the door could be opened to a lucrative career as a stock photographer.

High quality

In the studio, meanwhile, this incredible resolution means you can now match the quality of a 6x7cm film camera with a 35mm-style digital SLR.

But it's not only Canon's new 16.7 megapixel resolution that makes it a significant development. There's also the fact that it uses a CMOS sensor that's capable of producing images with little of the noise or chromatic aberration (fringing) issues that have dogged some other high-end digital SLRs such as the Kodak Pro14/n.

Add to that the full-frame capture you get from the 24x36mm sensor and you can see why the 1Ds Mark II is such a tempting proposition for professionals in all areas. Not only does this mean that your wideangles really are wide-angled, but there's no lens magnification to narrow the field of view.

Whether the 1DS Mk II will appeal to amateurs affluent enough to buy this is another matter entirely. This is a camera built without compromise. For a start, it's big and heavy; tipping the scales at over 2kg with a typical zoom lens and memory card.

Some 320g of that, the bottom 3cm of the camera, is accounted for by the battery, which is a heavy-duty cell that's good for 1,200 shots before it needs recharging. While it adds significantly to the weight, it's well worth it to know you're not going to run out of juice at a crucial moment when you're on location.

The EOS 1Ds Mark II is also stuffed to the gunnels with just about every advanced feature you could imagine. However, this makes it potentially complicated and confusing for those whose requirements are not so demanding.

For anyone wanting a '35mm' SLR with the ultimate current pixel count, Canon's update of its flagship model is in a class of its own. The increase from the 11.1 million pixels of the original EOS 1Ds to the 16.7 million pixels of the Mark II version places it fully at the front of the pack.