Introduction

The Nikon Coolpix S640 is an ultra-compact digital camera with a 12 megapixels sensor, a 5X stabilized wide-angle optical zoom lens and a 2.7" LCD. It packs all this in a 0.8" slim body. The optical zoom lens has a versatile range equivalent too 28-140mm. The Nikon S640 has a wide range of ISO sensitivities, from 100 to 6400.

Headline features of the S640 are ultra-fast autofocus system and near-instant shutter-lag. Nikon claims that its autofocus speed rivals DSLR cameras, see further down this review for all the details.

Exposure on the S640 is entirely automatic. Aside from +/- 2 stops of exposure-compensation, exposure is controlled by the camera alone. With a choice of center-weighed or evaluative metering, this camera shows little flexibility.

Suitability

This small ultra-compact distinguishes itself by a wide-angle lens which makes it suitable for photography in close-quarters. Landscape and architecture shots can greatly benefit from a wide-angle lens. The focal-length, being equivalent to 28-140mm in 35mm terms, should render flattering portraits and even more distant things.

While the Nikon S640 is a general purpose point-and-shoot camera, its feature set is rather limited and gives almost no direct controls to the photographer. Custom white-balance and focus-point-selection are the main direct controls. Note that the shutter-speed range goes from 1/1500 to 4s. This is neither quick enough for fast action, nor long enough for night photography.

There is no optical viewfinder on the Nikon S640 but its 2.7" LCD with 230,000 pixels is among the very best on an ultra-compact digital camera. The LCD shows really good outdoor visibility, thanks to an anti-reflection layer which also provides a broad viewing angle. The claims of higher contrast seem to hold true, as this display can show a good dynamic range, similar to that of images captured. This greatly helps judging if exposure is good or not, particularly in the absence of a histogram.

The Nikon Coolpix S640 also records 640x480 30 FPS movies in single-shot or continuous focus modes. It has is a Panorama mode which helps take a sequence of images in any direction, locks exposure and focus and disables all settings including ISO, WB, Flash, EC and drive-mode. The majority of remaining features are standard among this class of cameras. The ones that are not are covered in more detail in the next section. Audio can also be recorded either along-side an image.

Usability

As the S640 is one of the smallest cameras, its size is not without compromise. The build quality is excellent everywhere except for the flimsy but flexible battery-door compartment cover. The tiny rubber bands holding the mini-USB and AC-adapter covers do not look like they can use a lot wear-and-tear. Since this digital camera only recharges via USB, at least the USB cover will get a lot of use. Not only that, the camera is trapped while charging, requiring more care and fiddling if you want to keep more than one charged.

Its nice but its slippery front surface lacks any type of grip. On the rear, a small depression with 4 protruding dots provide the only purchase on the camera. The wrist-strap provides security from accidental falls. A poorly placed tripod socket is found at one end of the camera casing.

The camera is powered by a recessed but easy to use button on the top-panel. Next to it is the shutter-button which has short travel and is quite responsive. All other controls are easily accessible around the combined dial and 4-way controller. The rotating dial is used in record mode to scroll through options. In playback mode, it quickly scrolls through images.

The zoom is operated electronically via a rocker switch surrounding the shutter-release. There are 12 steps to the zoom which is a coarse granularity for a 5X optical zoom lens.

The Camera/Scene/Movie button activates a mode-selection menu. Pressing the shutter does not exit the virtual mode dial, instead the mode or OK button must be pressed. This means that the Nikon Coolpix S640 is not always shooting-priority. The Play button enters playback mode. To exit, either tap the shutter or press the Camera button.

There is an Auto mode which is used for general-type shooting. There are 18 scene modes to choose from, including panorama-assist mode. Two special modes are kept separate: smart portrait and subject tracking. Smile portrait has its own menu items to control skin softening, smile detection and blink-proof. Subject tracking tries to keep a moving subject in focus. The focus mode used for subject tracking is not accessible outside of this mode. The last mode-selection option is movie-mode. Finally, in Auto-Scene mode the camera guesses which scene-mode would be required and takes the shot in that scene-mode

The Menu button obviously activates the current mode's menu. The Delete button works both in Shooting and Playback mode. In Playback mode it affects the image shown. In Camera mode it affects the last picture taken. In both cases, it asks confirmation before deleting the target image.

The central control is the rotating 4-way controller. Each direction is assigned a function in Shooting mode. Up is for Flash-mode. Right is for exposure-compensation. Down is for macro-mode and Left selects the self-timer. A direction button invokes the list of options. To make a selection, either the vertical buttons or rotating dial must be used and the OK button must be pressed.

The 2.7" LCD shows each image after it is taken. There is no way to disable this, so we cannot know if it would be any faster without the image review.

The S640 uses SD or SD-HC memory cards, which are presently the cheapest and most common form of flash memory. Images are numbered in a standard form but the number keeps increasing even after changing the memory card. Not only is this rather annoying, there is also no menu option to reset the counter to zero. Then again, maybe only camera reviewers care about this.

Performance

Overall, the Nikon Coolpix S640 shows a rather good performance for a modern ultra-compact. Although its images show noise from ISO 100, it is very fine and well under control. At ISO 400, medium-sized prints are still possible as only fine details get seriously affected. ISO 800 and 1600 can be used for emergencies.

Nearly every other aspect of image quality is quite good. Colors are natural, if a little subdued, and the automatic white-balance is impressive, even under artificial light. Distortion is low throughout the zoom range, showing only a hint of barrel distortion at wide-angle. The lens is not very sharp but there is good consistency of across the frame. It does show pronounced purple fringing in zones of high contrast though.

The most important feature of the Nikon Coolpix S640 is its autofocus speed. Nikon says it features DSLR-like focusing speeds. It is hard to disagree as DSLRs can be very variable in this regard, depending on the model and lens used. That being said, this digital camera is probably the fastest-focusing ultra-compact to date. It is highly variable though.

At its best, the S640 focuses in under 1/3s. It can do so consistently in good light for typical subject distances. It slows down considerably for macro focusing which can take up to 1s. The downside of this ultra-fast focusing system is that it gives up quickly and more often than any camera reviewed here. Unlike the S610, when the S640 fails to lock focus, it simply gives up, rather than locking the focus incorrectly.

This digital camera is extremely responsive most of the time. The only slow aspect is the shot-to-shot speed of just under 3 seconds. During these 3 seconds, button presses are mostly ignored. Outside of this interval, the S640 responds incredibly fast. Image playback moves at blazing speed. Zooming and scrolling around is also much faster than an most ultra-compacts.

Playback mode is very simple but does include image information and a histogram, just press the OK button while an image is shown fully. When zoom-in, the OK button cancels the zoom.

The continuous shooting is nothing short of useless. At 0.8 FPS it is very slow but the LCD does not even keep up, so shooting a moving subject is nearly impossible. The camera's built-in image stabilization, called VR for Vibration Reduction, is very good. As is macro focusing near wide-angle.

Battery-life is about average by modern standards. The emphasis is on modern because ultra-compacts used to be able to take over 500 shots. Nowadays, 270 shots per charge (CIPA standard) is average.

Conclusion

The Nikon Coolpix S640 is one of many ultra-compact point-and-shoot cameras with a wide-angle lens. This model manages to stand out by its ultra-fast autofocus system, something which is unmatched among such small cameras. This feature makes it more usable for moving subjects than other cameras in its class.

The remaining features are barely minimal and one can find many more capable ultra-compact digital cameras. This is no reason alone to dismiss the S640 as it gives it simplicity and usability. For the target user who rarely jumps into menu system, its basic point-and-shoot feature-set may be all that's needed. In fact, the S640 makes the time between pointing and shooting quite short.

The image quality, without being top-of-class, is very reliable with reasonable noise-levels, good color, very good white-balance and barely any optical distortion. This makes it easy to forgive the purple-fringing and other minor problems listed earlier. The only two weak areas are the occasional failure to lock focus and the long gap required between shots.

Competition wise, the undeniable superior to the S640 is the Fuji Finepix F200 EXR which not only shows the most impressive image quality in its class but also a very complete feature set including manual exposure, a stabilized 5X wide-angle optical zoom and a rather speedy overall performance.

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