There are profound differences between digital SLRs and 'compact' or 'prosumer' cameras. It's not just the radically different optical viewing system employed in the SLR design, but the sensor size too. Non-SLRs use sensors the size of a child's fingernail.

The actual imaging area of a 1/1.8-inch sensor (the size usually found in high-end compacts) measures approximately 7.2mm x 5.5mm. The sensor in the average entry-level digital SLR measures around 21mm x 15mm. That's around nine times the area and the reason why even a modest 6- megapixel D-SLR will offer sharper images, less noise and higher ISOs than any 8- megapixel compact.

Pixels, as we keep saying, aren't everything. That's why high-end 'prosumer' compacts have been having a tough time. Once, every keen photographer aspired to one of the cutting-edge 8- megapixel flagships, such as the Sony F828,

Olympus C-8080, Canon PowerShot Pro 1, Nikon CoolPix 8800 or Konica Minolta A200. Now though, you can get a D-SLR for the same money or less. But that's all changed. The Sony DSC-R1 marries a D-SLR size sensor to a prosumer body, offering - we hope - the best of both worlds.

It has a wider zoom range than any D-SLR/kit lens combination, a fixed lens that eliminates sensor dust problems, and yet offers the image quality that only a physically large sensor can provide.

Actually, the Sony goes one better. It uses a brand new 10-megapixel sensor which easily outstrips (in megapixel terms) entry-level DSLRs, even Canon's 8-megapixel EOS 350D. It all sounds too good to be true, doesn't it?

First, let's take a tour through the DSC-R1's feature highlights. You'd have to pay £1,300 for a Nikon D200 to match the Sony's 10-megapixel resolution, and that's for the body only. To beat it, get ready to part with £2,000 for a Canon EOS 5D (body only, again).

And how about that lens? The 24mm wide-angle setting is usefully wider than the 28mm of any SLR's kit lens, while the 120mm longest setting easily outstrips the 90mm or 105mm maximum of its rivals.

Unlike D-SLRs, the DSC-R1 doesn't have a mirror. This means the designers have been able to position the rearmost lens element a mere 2.1mm away from the sensor. The argument is that this enables an optical design which reduces chromatic aberration.

Larger sensors use more power, but the use of a CMOS chip rather than the usual CCD design keeps consumption within manageable bounds. Indeed, you should be able to get 500 shots on a single charge. That's hardly exceptional by D-SLR standards, but it's good for a prosumer model which does, after all, have to power an LCD display as well.

Sony has implemented its usual infoLithium technology to display a constant readout of the battery's (predicted) remaining life, in minutes. It's a nice idea in principle, but different types of usage place different demands on the battery and hence constant re-calculation of how long it will keep running. It's not as useful as it sounds.

Like all prosumer cameras, the DSC-R1 offers digital rather than optical viewing. There's an eyepiece for the camera's 235,000-pixel EVF on the back and a larger 2-inch, 134,000-pixel LCD for composing shots with the camera held away from your eye.

Unusually, this is on the top of the camera rather than the back, though it has a tilt-and-swivel mechanism so that you can view it at practically any angle. And then there's the ISO range. D-SLRs usually stop at ISO 1,600, but the DSC-R1 goes one stop further, to ISO 3,200.

On paper, this camera's specifications, features and value for money look absolutely staggering. But you don't use cameras on paper, you use them in the real world, and the DSC-R1's got to pass this test too.

This is not a pretty camera. It consists principally of that big fat lens, on the back of which is a roughly rectangular 'body' which is dwarfed by the optics. And on the right of this rather diminutive body is an oversized handgrip.

The shape is, at least, quite practical. It handles no worse than the average compact D-SLR, though it's not as wieldy as the excellent Nikon D50/D70s, and that huge lens does give it a somewhat awkward weight distribution.

The startup time isn't bad. Sony quotes a time of just 0.68 seconds. That's good for a non-SLR, though modern SLRs start up so fast there's essentially no delay at all. And it's D-SLRs that the DSC-R1 is up against - there are no prosumer cameras in its price range.

The zoom ring is manual and mechanically linked. You take that for granted on a D-SLR, but it's a welcome change for non-SLR users who are accustomed to the feeble, stodgy reactions of press-button zoom motors.

There's a manual focusing ring too, but here you come up against a fundamental difference between prosumer and D-SLR design, and one that's got nothing to do with megapixels. The electronic viewfinder doesn't have the resolution for manual focusing.

Also, the image doesn't 'snap' in and out of focus, possibly because EVFs don't have the instant reaction of optical systems. The moment you turn the ring, the image is enlarged to aid focusing accuracy, but it's not enough.

This isn't a selling point, it's a cack-handed solution to a problem you shouldn't have. In fact, the best way to focus 'manually' is to use the push-button AF control - the camera focuses as you hold the button in, then retains that focus position when you release it.

Isn't it about time camera makers started using good, high-resolution EVFs? The 235,000 pixels in this one sound a lot, but the image is still gritty and lacking in detail. Konica Minolta experimented with a 1-megapixel EVF in the DiMAGE A1, and it's a shame other makers didn't follow suit.

Of course, you could use the 2.0-inch LCD on the top. You can flip it out and rotate it to compose shots with the camera held out at arms length in front of you, or you can fold it flat and use it to compose shots at waist level. But remember to switch off the EVF's auto-sensor.

With this enabled, the camera automatically switches from the LCD to the EVF if the eyepiece sensor is covered up (usually, by your eye). Hold the camera close to you at waist level, though, and it will have the same effect, annoyingly blanking out the LCD at the very moment you planned to take the shot.

And it's hard to find any logic in the button layout. The ISO button is by the shutter release, the AE lock button's on the back, the metering, bracketing and self-timer buttons are on the back to the far left, while the flash, white balance and focus controls are on the left side of the lens barrel.

You'll remember it all eventually, of course, but until you do you have to check three or four possible locations to find the button you want.

The rear of the camera hosts a secondary control wheel, similar to those on the back of some EOS SLRs. The action's a bit heavy for rapid thumb-spinning, though. In the middle of this is a fiddly joystick for menu navigation.

The DSC-R1 lacks the finesse of the digital SLRs which are its price rivals. Whatever its technical merits, as a camera, it's more awkward and not particularly satisfying to use.

But what are the pictures like? The captions accompanying the sample shots with this review offer more detail on specific characteristics. Broadly, though, it's very good. But it's not a great leap forward.

Interestingly, when you examine its images closely they have the same glassy-smooth look as those of the EOS digital SLRs - which also, of course, use CMOS sensors. Fine detail is good, but it's debatable whether the DSC-R1 can resolve significantly more than the Nikon D50/D70s, say. The files are bigger, but the per-pixel detail's also a little 'woollier'.

The colour and overall colour rendition, though, is very good. The auto white balance produces consistently bright, natural-looking shots and for the most part the multi-pattern metering does a good job without any manual interference. Having said that, any camera in this price bracket can be relied on to do the same.

The only exposure problems encountered in our test boiled down to the controls rather than the camera. Most cameras use a now-standard method for applying EV compensation - you hold down a button and rotate a control wheel. On the Sony, EV compensation is applied simply by turning the control 'dish' on the back.

While you're still getting used to the camera it's all too easy to turn the wrong dial while you're trying to make adjustments or - as in this case - you hand the camera over to someone else to look at, not realising they've turned the dial. The EV compensation is 'sticky'. It still applies after the camera's been shut down and restarted. In this instance, a dozen shots got spoiled before the error was spotted.

The DSC-R1 will probably sell by the truckload because of its resolution, its sensor size, its photographic controls, its zoom range and its price. Technically, it's a fascinating camera, and would make a great talking point for pub gatherings and camera clubs.

As a photographic tool, it's less impressive. Whatever the merits of the sensor and the lens, the electronic viewing system is a major drawback. The design is either 'bold' or 'bizarre', depending on your own aesthetic sensibilities, and the control layout has little to commend it.

The DSC-R1's size, appearance and unique top-mounted LCD will attract plenty of attention, but they don't help you take pictures more effectively.

But the DSC-R1 is encouraging in other respects. Does it mean camera manufacturers will start including big sensors in compacts? If so, we could see another step up in image quality that the current megapixel war seems incapable of providing.

And don't overlook the fact that Sony makes sensors for many other camera manufacturers. Clearly, they now have the ability to produce a large, high-resolution sensor at a mass-market price? Where is this sensor going to appear next, we wonder...?

Via PhotoRadar