While Nikon pushed a series of low-cost and mid-range digital SLRs in the past few years, the D300 hung on at the high-end, $1700 position in the lineup for nearly three years. Now it’s been replaced with the D300S, a modest upgrade that adds the same mediocre 720p video capabilities found on the much less expensive D90, along with dual memory cards, a slightly faster burst rate anda few additional tweaks. Make no mistake: the D300S is a strong performer, with extensive customization options, rugged construction and solid results in our lab tests. When it comes to innovation, though, there’s not much new in this new camera.

Like its predecessor, the D300S is a hefty handful, weighing in at nearly two pounds for the body alone. This substantial size is explained by solid construction, with a magnesium alloy body and extensive weatherproofing.

The D300S offers the same 12.3-megapixel resolution as the D300, and the same excellent 100% viewfinder. The 51-point autofocus system, with 15 cross-type points, also remains the same, which is a good thing: it’s hard to argue with fast and accurate. The 3-inch 921,000-dot LCD is familiar from several Nikon models, but still a welcome feature.

One new feature we really like on the hardware side is the inclusion of both SD card and CompactFlash slots. This provides several benefits. You can have your shots saved to both cards simultaneously, providing instant backup copies for mission-critical assignments. When shooting RAW+JPEG, the two versions of the same shot can be saved to separate cards. And, of course, you can shoot as usual and have more overall capacity at hand without stopping to fish out a new card.

Live View looks good, but it’s not much use when shooting moving subjects. You have your choice of slow contrast-detect focusing or blanking out the Live View display momentarily and using the standard phase-detect autofocus. With either option, though, there’s a long beat between the time you press the shutter and the moment the picture’s taken.

The customization options are as wide and as deep as you could ask for, and groups of settings can be saved in banks to quickly adjust the camera to the task at hand. However, after a few unchanged generations, the button control scheme is starting to feel a bit antique. You have to hold down a button and turn a control dial to change shooting modes, white balance or ISO settings, which is clumsy compared to a simple mode dial. The quick menu is limited to a few shooting controls, and no real effort has been made to make the learning process simpler. To set a custom white balance, for example, you have to hold down the white balance button till an indicator blinks in the monochrome LCD, then take your shot of a white surface. Once you know your way around the camera, much of this becomes second nature, but the learning curve is steep.

Performance (read in-depth performance coverage at DigitalCameraInfo.com)
The Nikon D300S did well overall in our testing, but nothing blew our socks off. The color accuracy is exceptional, and image noise was very low under bright light, and decent in our long-exposure, low-light testing. Resolution results were superior to most tested SLRs, but the Canon 7D, the Nikon’s closest competitor, scored slightly higher, notably when it comes to image sharpness. The dynamic range results were strong at low ISOs, but the ability to maintain detail in high-contrast situations fell off more sharply than most as ISO levels increased. The white balance system accuracy was acceptable but unimpressive. One strong suit of the D300S is the pleasure you feel during continuous shooting; the camera delivered more than 7 frames per second shooting large fine JPEGs.

As to video capability, the D300S maintains the underwhelming 720p, 24fps system introduced in the D90 at the tail end of 2008. Color accuracy and video noise results are fine, but the rolling shutter problem (where the image seems to wobble when you pan quickly) is a continuing problem, image sharpness was sub-par, and the lack of manual controls doesn’t stack up well against the competition.

Comparisons (read in-depth comparisons at DigitalCameraInfo.com)
The main competitor for the Nikon D300S is the recently released Canon 7D. The two cameras carry the same pricetag, at $1699 for the body alone, and have similar size, construction and customization options. The Canon brings 18-megapixel resolution to the party cmopared to 12.3 for the Nikon, but actual image sharpness favors the Canon by just a hair. For video recording it’s no contest: the Canon’s 1080p high-def video, with extensive manual control, is good enough to attract attention from professionals, while the Nikon’s 720p video pales in comparison. In performance testing, the Nikon produced miore accurate color and lower image noise, the Canon won the resolution face-off, had a wider dynamic range and was slightly faster in continuous shooting. We do prefer the Canon control scheme, which is more flexible and intuitive. In the end, though, these are not likely to be the first SLRs anyone buys, and the decision is likely to rest with brand loyalty and lens collection.

The far less expensive Nikon D5000 at $850 including an 18-55mm kit lens, is no match for the D300S when it comes to construction or customization, and the 2.7-inch 230,000-dot LCD lacks the visual sizzle of the D300S display (though the D5000 screen does swivel, a particular advantage when shooting video). In our lab tests, though, the differences between the two 12.3-megapixel cameras were not as wide as you might expect. In fact, the Nikon D5000 posted superior scores in color accuracy, long exposure, white balance and image noise, though its resolution results were distinctly inferior, and the burst  speed is much slower at around 4 shots per second.

The Panasonic GH1 sells for $1500, but that figure includes an impressive 14-140mm lens (equivalent to a 28-280mm in 35mm photography) that allows video shooters to autofocus continuously and silently while shooting, a rarity among still cameras. Even when shooting stills, Panasonic delivers Live View autofocus speed that smokes the competition. the GH1 is a Micro Four Thirds camera, though, not a true SLR, which means you’ll line up shots using either the LCD or an electronic viewfinder. And with a smaller sensor size, we found significantly higher image noise levels than the Nikon produces. Another key Nikon advantage here: the Panasonic’s top burst speed is a so-so 3.13 shots per second.

Finally, on the topic of innovation, the $1050 Sony A550 makes an interesting comparison case. Like all Sony SLRs to date, the A550 lacks any video recording mode at all, a significant ding in the current market. However, Sony uses a dual-imager Live View mode that is as fast as shooting with the optical viewfinder, a major accomplishment. The A550 includes handheld in-camera high dynamic range shooting. a unique capability. And despite a much lower selling price, the 14.2-megapixel camera holds its own in our lab tests, outscoring the Nikon on resolution, dynamic range and white balance while the Nikon has the advantage in color accuracy and a slight edge in image noise, and burst rate speeds are neck and neck. The Nikon D300S, designed for higher-end users, is more solidly built, more customizable, and has a more accurate viewfinder. Still, we do wish Nikon would show some of the ingenuity that Sony displays here.