If you’re looking to buy your first digital SLR, you’re spoilt for choice — or possibly overwhelmed by the options.

In the last few months we’ve seen new entry-level digital SLRs from three of the big names in the camera business — Canon, Nikon and Olympus — and Sony has also entered this market, using camera technology bought in from Konica Minolta.

To be honest, these cameras are more similar than different. All four are aimed primarily at people making the jump from a compact digital camera to an SLR — people who already understand the digital half of the equation and want to upgrade to an SLR to take their photography further. An SLR is more responsive than a compact, allowing you to take photos more quickly; it gives you more control, so you can be more creative; and it’s more flexible, allowing you to change the lens or use accessories such as flashguns and remote controls.

Because these entry-level SLRs are designed for people who are used to pocket-friendly compacts, the manufacturers have kept them small and light. Experienced photographers may scoff, telling you that larger and heavier cameras are easier to handle and hold, but if you’re used to a compact, you won’t want anything too big. If size is absolutely everything, the Olympus E-410 is the smallest and lightest of the cameras featured here.

The Canon EOS 400D Olympus E-410 and Sony Alpha DSLR-A100 both have 10-mega pixel sensors, while the Nikon D40 lags behind with just 6 mega pixels. This is enough for most purposes, including prints up to A4, but it gives you less scope for cropping your images or making poster-size enlargements. Since many top-end compacts now offer 7 or even 10 mega pixels, you might feel behind the times with the D40, although pixels aren’t everything — you’re still getting the benefits of a physically larger sensor and a bigger and better lens, so the D40 will produce better images than a compact.

The Canon EOS 400D and the Nikon D40 both ship with 18-55mm zoom lens, although the 35mm equivalents are slightly different (because the cameras have slightly different sensors), with the Canon lens offering the equivalent of 29-88mm and the Nikon 27-83mm. The Sony Alpha DSLR-A100 comes with an 18-70mm lens, or 27-105mm in 35mm terms and the Olympus E-410 comes in a twin-lens kit with 14-42mm and 40-150mm lenses, or 28-84mm and 80-300mm in 35mm terms.

In the short term, the Sony and Olympus cameras gives you a better zoom range out of the box, but in the long term, Canon and Nikon offer more lenses and other accessories. If you can imagine buying additional lenses in the future — for example, if you might want a telephoto lens for photographing wildlife — go for the Canon 400D or the Nikon D40. Both cameras are compatible with a wide range of lenses, flash guns, remote releases and so on.

What about other features? The Nikon D40 has a beginner-friendly menu system, with sample images that help you choose the right settings. The Sony Alpha DSLR-A100 has built-in image stabilisation for taking pictures in low light (Canon and Nikon offer image stabilisation via special lenses). The Nikon D40 uses SD memory cards, whereas the others take Compact Flash, although the Olympus E-410 also accepts xD memory cards. The Canon EOS 400D, Olympus E-410 and Sony Alpha DSLR-A100 have cleaning modes that vibrate the sensor to shake off dust.

So which is best? As you can see from the scores, it’s a close-run thing, but for our money, the Canon 400D has a slight edge. It costs a little more than the Nikon D40, but the extra mega pixels will keep you happy for longer.

The Nikon D700 offers a boat-load of features previously the exclusive domain of the D3 and D300 cameras and manages to pack it all in a D300-style body with a $2,000 savings added as incentive. Just like someone said: “With a Nikon D300 and Nikon D700 you would have high ISO, long reach, wide angle FX capability, and two semi-pro bodies that share accessories. Nikon is just filling in the gaps between their models so this is a body for everyone. It could also be a great 2nd body for D3 users who want two cameras that are both FX but one which is smaller and lighter”, it’s a new camera Nikon made for people looking for FX in a semi-pro body.

The headline feature of the D700 is of course its full-frame sensor, with the same 8.45-micron pixel pitch and 12-channel data readout from D3. As a result, the D700 has the D3’s renowned image quality at high ISO, but in a smaller, more affordable form factor. Like the D3, ISO ranges from 200 to 6,400, with Lo 1 (100), Hi 1 (12,800), and Hi 2 (25,600). We’ve noted a few differences in overall performance from the D3’s images, however, with a little better control over red saturation, and detail in the JPEGs that resembles what you get from well-processed NEF files from the D3. The D700 also features the same innovative EXPEED high-speed image-processing system, 14-bit A/D conversion and 16-bit processing pipeline to provide the detail and smooth gradation necessary for outstanding print enlargement and reproduction.The D300’s Integrated Dust Reduction made it into the full-frame D700 as well.

Also pulled from the D3 bag of tricks is the same Multi-CAM 3500FX autofocus sensor module featuring 51 AF points, the Virtual Horizon Indicator from the D3 (which is now active in Live View mode as well), the two Live View modes (Handheld and Tripod),the high-resolution 3-inch LCD monitor with tempered glass providing a 170 degree viewing angle.

The Nikon D700 additionally shares a number of features with both the D3 and D300. All three sport a powerful 51-point AF system, a high resolution 3in VGA monitor with Live View, the same 1005-pixel metering system, along with an HDMI port for connection to HDTVs – albeit using a mini-jack on the D700. All three are also very tough, offering resistance to dust and moisture.

Much has also been written about how the D700’s continuous shooting and viewfinder are inferior to the D3, the Nikon D700 offers 5fps continuous shooting compared to the D3’s 9fps,but add the optional MB-D10 battery pack and EN-EL4a battery to the D700 body and this can jump back up to 8fps.

Unlike Canon’s full-frame models you can still use lenses designed for cropped bodies on the D700. Fit a DX lens and you can either shoot in a cropped 5.1 Megapixel mode, or with the full sensor area and resolution – albeit with a reduction in quality beyond the DX frame.

Then, who should buy a D700? It’s for anyone who wants to shoot handheld in low light (at higher ISOs than you would ever consider with a D300, like 6400 ISO). It’s for anyone who really wants the advantage of shooting with a 35mm-sized full-frame sensor, and it’s for anyone who just wants better looking images than they’re getting now with a D300 or lower. So, in short, if you’ve dreamed of a D3 without the D3 pricetag, your dreams have finally come true in the Nikon D700.