Overall handling and operation
Ever since the launch of the D40 back in 2006, Nikon has been making little entry-level cameras that are uncomplicated and easy to use, but with plenty of manual control on offer. The D3100 follows in that tradition, being a generally pleasant camera to shoot with (indeed distinctly more so than most other entry-level DSLRs). The additional controls that have been added to the basic D40 design - the live view switch, movie record button and drive mode lever - are all well-considered and sensibly placed, subtly improving the shooting experience.
In the Auto and scene modes, the camera behaves very much as a point-and-shoot, with very little user intervention required or allowed (you get control over focus and flash modes, but that's about it). For novice users wanting to take a bit more control, the Guide mode offers a friendly-faced way of learning a bit about setting apertures and shutter speeds. Unfortunately though, it makes no attempt to take advantage of live view and show the user the effects of any changes on the picture they're about to take- something that dedicated, full-time live view cameras like the Sony NEXs and Panasonic GF2 do better.
It's on switching to the PASM modes that the D3100 really comes into its own. The basic exposure parameters - shutter speed, aperture, and exposure compensation - are all handled by the well-placed rear thumbwheel in concert with the exposure compensation button, which (as on all Nikons) is placed behind the shutter release for operation by your index finger. This layout makes changing these settings as quick and fluid as on any other camera in this class. We also like Nikon's dedication of the the four-way controller to selecting a focus point manually - combined with the 11-point AF system this makes focusing on off-center subjects a breeze, without having to always focus and recompose for every shot.
The other shooting controls - ISO, white balance, focus mode and the like - are all set from the active control panel on the rear display, which is intuitive and well-implemented, although inevitably a little slower than direct-access buttons. Pressing the 'i' button 'activates' the control panel, and the desired function can then be selected and changed using the four-way controller. A select few options (image size/quality, ISO, white balance and Dynamic Range Optimization) can also be assigned to the Fn button for 'one touch' access. The net affect is to make the camera quick to use, with almost all the major controls at your fingertips - although with one exception.
Specific handling issues
Probably the only real gripe we have regarding the D3100's handling when used in conventional eye-level fashion is to do with setting the ISO. This is a parameter that we think should be easy to change with the camera to your eye, using a button that's easily identified by feel alone, and without having to shift your grip on the camera with either hand. This has become increasingly desirable as higher sensitivities have become more and more useable without huge image quality compromises. But while some other manufacturers have recently made a point of repositioning their ISO controls to make them easier to operate, Nikon's designs have pretty well stood still for the past four or five years.
On the D3100, the only way to change ISO via an external control is to assign it to the 'Fn' button. This is reasonably well-placed for operation by your left thumb with the camera to your eye, but because of its close proximity and identical shape to the flash button, the two are still easily confused when working by feel alone. This means it's all-too-easy to pop the flash up by mistake when you meant to change the sensitivity. We'd be much happier to see ISO operated using the button currently assigned to 'info', which is a function you never need to access with the camera to your eye.
Upgraders from compact cameras should probably also be aware that Nikon's Auto ISO does not behave in the way they might expect. Whereas all other brands program Auto ISO in a fashion that's designed to combat camera shake (or blur from relatively slowly-moving subjects) by automatically increasing the ISO at a shutter speed determined by the focal length of the lens, Nikon's approach uses a single, user-specified minimum shutter speed, which has to be carefully selected for the specific situation and focal length being used. To be fair this method has a real advantage for sports and action work, but it also makes Auto ISO distinctly unsuited to general 'walkaround' use with a zoom lens. Overall we don't think it's particularly well-suited to this class of camera.
To compound all this, the D3100 only ever shows the ISO in the viewfinder when you're changing it, which feels a little dated compared to other recent entry-level models such as the Pentax K-x and Canon Rebels which display it permanently. Indeed, when you have Auto ISO set, you can only ever see the value the camera chose by reviewing the shot after the event. Now that ISO is effectively just another exposure parameter alongside shutter speed and aperture, it would be nice to see Nikon paying more attention to making it easy to control.
The D3100 is overall a pretty fast, responsive camera, and rarely makes you feel like you're waiting for it to do something. Its overall operation in everyday use - changing settings, browsing images in playback and the like - is certainly as quick as it needs to be, which is all you can really ask for. Notably Nikon has fixed one of the biggest irritations with the D3000, i.e. substantially reduced performance with Active D-Lighting enabled, and the D3100 is now to all intents and purposes just as fast whether ADL is turned on or off.
At around 3 fps, continuous shooting is quite respectable without being class-leading - we suspect it will keep the vast majority of users perfectly happy, although if you're looking for a really fast-shooting entry-level camera there are better options available. Autofocus is very much lens dependent, and the 18-55mm kit zoom isn't a speed demon, but again it's likely to satisfy most potential buyers. However it's worth bearing in mind that, like all DSLRs, the D3100 focuses more slowly in Live View mode, although it's nowhere near as excruciatingly hesitant as most of its competitors.
Continuous Shooting and Buffering
We tested the D3100's continuous shooting using a fast Lexar Professional 8Gb 133x SDHC card, with the camera set to manual focus and a shutter speed of 1/500 sec at ISO 400. The camera consistently maintains a 2.9 fps shooting rate regardless of file format, und unlike recent Nikons at this level, turning on Active D-Lighting has little impact on the number of frames you can shoot before filling the buffer. Notably, the burst depth with DRO 'On' has increased dramatically, from the D3000's mere 5 JPEG frames to a very much more useable 20 frames.
The RAW buffer is a quite reasonable 8 frames, even when shooting JPEGs concurrently. Once the buffer is full the camera will continue to shoot sporadically at an average rate of around 1fps when space becomes available again, with occasional pairs of closely-spaced shots.
Even turning on the D3100's 'Auto Distortion Control' feature (which corrects the JPEGs for the lens's barrel or pincushion distortion) has little impact on speed. In JPEG with ADL On too, the camera will still shoot at 3fps for 10 frames, then 'throttle back' to about 1.6 fps and keep on shooting at this reduced rate for at least another 20 frames (which is arguably a more intelligent way of doing things anyway). In RAW + JPEG, Auto Distortion Control has essentially no effect on continuous shooting.
- JPEG (ADL Off): 2.9 fps for 24 frames, then approx 1 fps; 19 seconds to recover.
- JPEG (ADL On): 2.9 fps for 20 frames, then approx 1 fps; 19 seconds to recover.
- JPEG (ADL and ADC On): 2.9 fps for 10 frames, then approx 1.6 fps; 19 seconds to recover.
- RAW: 2.9 fps for 9 frames, then sporadic shooting as buffer clears; 13 seconds to recover.
- RAW + JPEG 2.9 fps for 8 frames, then pairs of frames at ca. 4 second intervals; 23 secs to recover.
Overall this is a perfectly respectable performance, but in no way class-leading. For example the Pentax K-x is substantially faster at almost 5 fps, and the mirrorless Sony NEX-3 and -5 can shoot at 7 fps.
Autofocus speed / accuracy
Like all of Nikon's other entry-level models, the D3100 doesn't have an in-body autofocus motor, which makes focusing performance highly lens dependent. This also means the camera won't focus non-AF-S Nikkor lenses, or third party designs which lack an inbuilt motor; something you need to bear in mind if you choose to expand your lens collection (and which limits your options on the second-hand market). Many of the most popular lenses bought by beginner photographers are now available either from Nikon or third-party makers, however.
As usual for a DSLR the D3100 uses two distinctly different autofocus methods - 'phase detect AF' for normal eye-level shooting, and 'contrast detect AF' when in live view. The former is distinctly faster, substantially because it's what the lenses' AF motor systems are designed for; we've had a lot of experience with it on cameras such as the D3000 and D90, and have found it to be very capable. Indeed while Nikon advises against it, the 3D-tracking mode is pretty effective at tracking moving subjects (a capability unusual in this class). However the contrast-detect method has the advantage of more flexible focus-point placement, and compact camera-like features such as face detection.
With the standard AF-S Nikkor 18-55mm F3.5-5.6 VR kit zoom, the focus speed is perfectly acceptable, but not spectacular (you really need to use a better lens for the true benefits of the D3100's sophisticated AF system to become apparent). It's noticeably faster using 'normal' PDAF than live view CDAF, although the latter is relatively fast compared to many other SLRs, and very accurate. For focusing from infinity to about 2m, we measured acqusition times of about 0.6 sec and 1.2 sec respectively.
AF-F focus mode for Live View / Movies
New to the D3100 is 'AF-F', a continuous autofocus mode for live view and movies that attempts to keep a moving subject in focus (i.e. more or less the same thing as AF-C). When combined with the 'Subject Tracking AF' mode, it will even do so while following the subject as it moves across the frame. This isn't ground-breakingly new stuff - Panasonic G series cameras have been able to do this for a couple of years, for example - but this is the first time it's been implemented on an SLR.
AF-F isn't, in truth, terribly well-implemented when shooting stills using Live View, because it still insists on initiating an entire CDAF cycle when you half-press the shutter to take the shot, and this somewhat defeats the purpose of using subject tracking to speed up focusing. Oddly it does this even when the AE-L button is set to 'AF On', which we'd expect to disable focusing with the shutter button (as it does in all the D3100's other focus modes), so that pressing it immediately grabbed a photo.
AF-F's main practical benefit, then, comes from following a moving subject when shooting movies. But while it can do this to a degree, its relatively slow speed means it doesn't work so well compared to mirrorless cameras which have lenses designed specifically for the purpose. This means movies shot using AF-F with the 18-55mm kit zoom can visibly drift out and and back into focus for a second or so as the system tries to keep track. It's improved by using the AF tracking mode (because the camera has a clearer idea of what it should focus on), but it's not entirely eliminated.
Another problem is that the internal microphone, positioned in the camera's shoulder close to the lens, is perfectly-placed to pick up any noise from the autofocus motor. Often this will be masked by ambient sounds, but in quieter situations the motor can be quite audible on your soundtrack. As there's no facility for connecting an external mic, there's not a lot you can do about this aside from turning sound recording off altogether.