The Nikon D3100 is the best entry-level digital SLR currently available. A host of features and excellent image quality sends this camera to the top of the pack. There are some half-baked ideas though, like the difficult full-time AF in video implementation, but this is something that can hopefully be worked out in future iterations.
14.2 megapixel DX-format CMOS sensor
3.0" LCD monitor (230,000 dots)
Image sensor cleaning (sensor shake)
11 AF points (with 3D tracking)
IS0 100-3200 range (12,800 expanded)
HD movies (1080p, 720p or WVGA)
The D3100 is the latest entry-level Nikon DSLR in a line that dates back four years to the D40 and, in arguably the biggest upgrade yet, gains two key features: live view and movie recording. Both of these were starting to look like awkward omissions, and are made possible by the D3100's new 14Mp sensor. Despite this it successfully continues the emphasis on offering unintimidating ease-of-use, with the controls for the new features unusually well-integrated into the body design.
However, while the D3100 represents a specification upgrade over a family of cameras we've generally liked, in some respects it has found itself rather out-paced by the market. When we reviewed the D3000 it was one of the only large sensor cameras that encouraged the novice user to make the most of its capability, and it did so without interfering with more hands-on operation of the camera. However this is becoming increasingly common, particularly with mirror less cameras that more readily replicate the compact-camera user experience while still offering DSLR-standard image quality.
The D3100 offers little to complain about in terms of image quality, and its new 14Mp sensor delivers very good results. High ISO performance is substantially improved over the D3000, to the extent that images shot at sensitivities as high as D3200 are eminently useable (although as is often the case with APS-C cameras, the extended 'Hi' settings equivalent to 6400 and 12800 are distinctly ambitious).
It offers a good amount of highlight dynamic range to prevent bright detail being lost (avoiding washed-out skies for instance) but this is often wasted by its default, 'matrix' metering mode that can overexpose in high-contrast conditions. Sadly the impressive low-shadow noise characteristics of the D7000 (and the other cameras using similar sensors), haven't yet filtered down to cameras in the D3100's class, so the image quality is pretty consistent with its peers.
The entry-level Nikons have always been among our favorites in this class to actually go out and shoot with, and likewise the D3100 is, on the whole, a very pleasant camera to use. The addition of the drive mode lever is a welcome update to the underlying D40 design, and the new live view/movie controls are well-placed and easily to operate. Nikon's trademark dedication of the four-way controller to AF point selection also makes the D3100 probably the best camera in its class for manual selection of off-center autofocus points. This, in turn, makes it easy to make the best of what is one of the most sophisticated AF systems available in this class.
If there's one quibble we have with normal shooting operation, though, it's to do with ISO setting (which is not Nikon's strong point in general). This is a control which we think should be easily changeable with the camera to your eye, which is ever-more important now that high ISOs are eminently more useable than they were just a few years ago. On the D3100 the only way to do this is via the customizable 'Fn' button, which is slightly awkwardly-placed on the left side of the camera, and easily mixed up with the adjacent flash activation button. Also the currently-set ISO is only displayed in the viewfinder when you're changing it (and never at all in Auto ISO) - many other cameras now display it all the time, which is far more useful.
Switch the D3100 into Live View and it soon becomes clear that while there are some things it's very good at, in other respects its behavior is distinctly less than perfect. It has unusually fast live view AF for an SLR, which goes a long way towards making the mode more generally useful for everyday shooting. It's still not as fast and seamless as the mirrorless cameras that are designed specifically for compact-camera style live view usage.
There are also a few odd behavioral quirks in live view and movie mode, with aperture control that can only be described as buggy. For example, the camera won't necessarily shoot videos at the aperture that's displayed on the screen when you press 'record', although it will when shooting stills. The lack of any kind of exposure level indication when using manual mode and live view is also a strange omission. What this means is that the D3100's two key new features simply don't work as well as they should - and crucially not as well as on competing models.
There's no doubt that the D3100 is one of the best entry-level SLRs available, offering very good image quality coupled with speedy operation and straightforward handling - at least for conventional eye-level use. Where it's less strong is in the implementation of the new features that have been added over the D3000, i.e. live view and movie mode. Neither is done badly, per se, and the improvement in CDAF speed is impressive, but they could still be better.
The D3100's guide mode is clearly aimed at attracting customers who have only used compact cameras, which makes the ability to offer a similarly fast live view focus and shooting experience a key consideration. And, while Nikon has done well to produce one of the better DSLRs in this respect (though the full time AF mode falls a little short of making live view use really immediate and fluid), both live view and video are quite simply done better by other cameras, particularly the D3100's mirrorless rivals.
Overall, we'd conclude that the Nikon D3100 is an excellent DSLR but make clear that a DSLR is no longer the only way to gain large sensor image quality at this price. As a result, while the D3100 would have been a stand-out camera 12 months ago, it's now simply a very good one in a market with plenty of equally good and potentially more interesting options.