The Nikon D4S will soon be making its way into the hands of professional photographers who have decided to upgrade to the flagship US$6,500 DSLR on the promise of improved speed and low-light performance over its predecessor, the D4. And if our brief hands-on with the camera at The Photography Show in Birmingham, UK, is anything to go by, it looks like they won't be disappointed.

Picking up the D4S you're instantly reminded how big, heavy, and generally sturdy professional DSLRs are compared to most other cameras. Measuring 160 x 156.5 x 90.5 mm (6.3 x 6.2 x 3.6 in) and weighing 1,350 g (2 lb 15.6 oz) the contrast between it and the likes of the Nikon D800 is massive … let alone smaller DSLRs or mirrorless cameras. But if you're in the market for a D4S, you'll already know this, and are probably used to lugging around a comparably bulky device.

At first glance it appears that the biggest change to the exterior design of the D4S is the addition of that S. However, on closer inspection (and with a side-by-side comparison with a D4) the subtle alterations become apparent. These include the rubber grip on the rear now expanding further across the back of the camera, a change of texture and material for some buttons, and the curves of the grips being slightly tinkered with. Though minor, the changes do seem to improve the ergonomics of the camera, at least to my hands.

With a newly-developed full frame (36 x 23.9 mm) 16.2 megapixel CMOS sensor and Nikon's Expeed 4 image-processing engine, the D4S has ISO settings which border on the ridiculous. It has a native range of ISO 100-25,600, and extended settings offer the equivalent of up to ISO 409,600. While some people argue such numbers are there only for the sake of marketing and that ISO has become the sequel to the megapixel race, there's no disputing that the D4S delivers when it comes to low-light performance.

Though I was only able to shoot in the exhibition hall (and not allowed to take any files home with me for better analysis) I was impressed by what I saw on the back of the camera. The D4S delivered surprisingly noise-free shots up to ISO 25,600. Even in its expanded range it delivered images which would be very usable if you needed to dial the ISO that high to get the shot. Quite frankly, it's mind-boggling to look down and see such big ISO numbers and get usable results.

Autofocus is just as blisteringly fast as you'd expect from a flagship professional camera, and has been improved over the D4 with the addition of a Group AF mode, which uses five AF points (the four surrounding one selected by the user) to improve tracking moving subject. This is especially welcome given that the camera can shoot 11 fps with AF tracking, and both features worked as advertised in my test (using a 24-70 F2.8 lens). That said, admittedly slow-moving trade delegates wandering around an exhibition hall isn't the ideal (or indeed the most rigorous) test of the D4S's ability.

Nikon says it's improved the sharpness, depth and skin tone of images produced by the D4S, but only being able to review images on the rear monitor, I can't say I was able to notice any discernible difference. Equally, I was unable to see what the jump to 60/50 fps Full HD video means for video quality. While my hands-on wasn't anywhere near long enough to test the life of the new battery, I was assured the D4S would go considerably longer on a single charger than the D4, though whether it will live up the standards of the D3S is yet to be seen.

Other updates which look like they could could make a difference to the D4S include the addition of being able to shoot in a small RAW file which allows considerably more images to be stored while retaining a level post-processing control, and the option to change the color of the rear monitor to match your studio monitors or personal preference.

The Nikon D4S appears to be another quality flagship DSLR which has been designed for a very specific market of professional photographers with a need for speed and low light ability. When the specifications for the D4S were released, some people said the improvements didn't go far enough to make it a worthwhile upgrade, but having spent an admittedly brief bit of time with the camera I feel the changes add up to a bigger improvement than they look on paper.

If you need a lightning quick professional camera which can shoot in any condition, the D4S could be the camera for you, especially if you're already a Nikon shooter or yet to invest in any particular system. If you're a Canon user, the question of whether the D4S is worth jumping ship for is another matter, and you'll probably want to see what Canon has to offer next before making that decision anyway.

Product page: Nikon D4S