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Performance

Note: because of the similarities in AF implementation between the D5100 and the D3100, certain portions of the analysis on this page are adapted from our in-depth review of the Nikon D3100.

Overall Performance

As we'd expect from Nikon's recent low-end DSLRs, the D5100 is quick and responsive in general use. Crucially, unlike the last-generation D5000, the D5100 is now to all intents and purposes just as fast whether Active D-Lighting is turned on or off.

At around 4 fps, continuous shooting is superior to the D3100 (which tops out at 3fps) and is respectable without being class-leading. We suspect it will keep the vast majority of users perfectly happy, but if you're looking for a really fast-shooting sub-$1000 camera there are better options available (like the 6fps Pentax K-r, for example).

As with all Nikon DSLRs that lack an internal AF motor, autofocus speed is very much lens dependent, and the 18-55mm kit zoom isn't a speed demon, and it's likely to satisfy most potential buyers. It's worth bearing in mind that like all DSLRs, the D5100 focuses more slowly in Live View mode, but Nikon deserves credit for improving focus speed in live view significantly over the last-generation. The D5100 just can't compete with the likes of the GH2 for contrast-detection AF speed, but it is significantly faster than the equivalent system in the Canon EOS 1100D/600D, which are painfully slow by comparison.

On the subject of live view, it is worth mentioning that there is approximately a 0.5 second delay between triggering the shutter in live view mode, and image capture. This is inevitable in DSLRs (and 0.5 seconds is comparable to the lag in the EOS 600D and Pentax K-r, for example) but it can cause problems in certain situations, especially when shooting portraits or moving subjects in the Effects mode (where it makes much more sense to shoot in live view).

Continuous Shooting and Buffering

The D5100 is the second camera we've encountered that is supposed to be able to take advantage of the latest SDXC with UHS-I (ultra-high speed) interfaces, the first being the D7000. The D5100's lower shooting rate of 4fps means that our conventional Class 6 SDHC was able to keep up with much of what the camera was able to throw at it but the faster SDXC card was able to improve the 'buffer full' rate by a fraction (around 0.2fps) when shooting Raw files.

The UHS-I standard is designed to allow cards with write speeds of up to 104MB/s, rather than the 45MB/s of the SanDisk Extreme Pro UHS-I we've conducted this test with. Based on this comparison between SDHC and UHS-I SDXC cards, we can't see them offering much benefit to D5100 owners.

Burst of JPEG Large/Fine images

Timing
8 GB SanDisk Extreme Pro
Frame rate 4 fps
Number of frames n/a
Write complete 0.8 sec

Burst of RAW images

Timing
8 GB SanDisk Extreme Pro
Frame rate 4 fps
Number of frames 16
Buffer full rate 1.8 fps (approx)
Write complete 10 sec

Burst of JPEG Large/Fine images

Timing
8 GB SanDisk Extreme Pro
Frame rate 4 fps
Number of frames 10
Buffer full rate 1.8 fps (2 frames in quick succession every 2 seconds)
Write complete 11 sec

The D5100 consistently maintains a 4 fps shooting rate regardless of file format, and unlike some previous-generation Nikon DSLRs, turning on Active D-Lighting has no impact on the number of frames you can shoot before filling the buffer. The D5100's JPEG buffer is effectively unlimited (the camera will stop shooting after 100 frames but another burst of 100 taken immediately afterwards), and the RAW buffer is reasonably impressive too, at 15 frames, dropping to 10 frames 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, in pairs of closely-spaced shots.

Even turning on the D5100's 'Auto Distortion Control' feature (which corrects the JPEGs for the lens's barrel or pincushion distortion) doesn't have a disastrous effect on speed. With the feature turned on, the D5100 can shoot large fine JPEGs continuously at 4fps for a perfectly reasonable 13 frames, before dropping to approximately 2fps.

Frame 1
Frame 2
Frame 3
Frame 4
Frame 5
Frame 6
Frame 7

The D5100's continuous shooting rate of 4fps might not be fast enough to capture the quickest action, but it is perfectly adequate for freezing moderate motion, like this skateboarder.

Autofocus speed / accuracy

As has already been mentioned, like all of Nikon's other entry-level models, the D5100 doesn't have an in-body autofocus motor, which makes focusing performance highly lens dependent. This also means the camera won't focus automatically focus with 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 D5100 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 D3100 and D7000, 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 D5100's 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 acquisition times of about 0.6 sec and 1.2 sec respectively. This is exactly the same performance that we recorded with the D3100.

AF-F focus mode for Live View / Movies

Introduced in the entry-level D3100, AF-F is 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.

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 D5100's other focus modes), so that pressing it immediately grabbed a photo. We'd almost put this down as a glitch in the D3100, and it is a shame to see that the D5100 displays the same (very odd) behavior.

AF-F's main practical benefit 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 will visibly drift out of and back into focus for a second or so as the system tries to keep track. Focus can generally be recovered with a half-press of the shutter button, and things are 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 and/or lens VR system. Often this will be masked by ambient sounds, but in quieter situations the motor can be quite audible on your soundtrack. Fortunately, unlike the D3100, the D5100 offers the provision for an external microphone.

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