First of all, it's important to understand where the Nikon D5100 fits in Nikon's capabilities. It is considered a "high-end enthusiast" D-SLR which means that it shares the same image sensor as the high-end D7000 without some of the higher-end features. If you're like me, very few of the D7000's features justify its extra cost and weight. The Nikon D5100 offers nearly the same image quality as its bigger brother in a less-expensive, smaller package, while adding a few tricks the D7000 doesn't have including an articulating display that helps you frame hard-to-reach spots.
Compared to its lesser-priced but still excellent brother the D3100, the D5100 offers improved image quality, speed, and resolution, along with a higher-resolution articulating display. For me, this is the sweet spot in Nikon's consumer D-SLR offerings.
The 18-55VR (3x) f3.5-f5.6 kit lens provides surprisingly good performance and image quality, although you'll likely outgrow it quickly. I have uploaded a few sample images taken with the D5100 and 18-55VR to show its performance and surprisingly good bokeh (pattern of blurred background) in large-aperture and macro shots.
For lens upgrades that include an AF-S autofocus motor, if you don't mind changing lenses, the Nikon 55-200VR is an outstanding value with excellent image quality, or consider the Nikon 18-105VR (5.8x) lens included with the D7000. If you don't mind some distortion and image softness, the 18-200 VRII (18x) lens may be your perfect "walkabout" lens. For me, I bought the pricey but outstanding Nikon 16-85mm VRII. Don't forget the Nikon AF-S 35mm f1.8 (if you can find it).
Low-light performance is outstanding with this camera, and the level of detail captured by the D5100 is excellent, even at higher ISOs. You're best capturing in RAW or RAW+JPEG mode (three different JPEG compression levels are offered) if you need to go back and fine-tune exposure or other settings after the shot. Nikon also offers "Active D-Lighting" which is a highly effective method for improving dynamic range of a photo to equalize the difference between high and low-light areas of a photo.
Interestingly, the improvement in image quality compared to my D5000 isn't dramatic. Given the incredible improvement I saw when upgrading from my Nikon D60 to the D5000 perhaps I had unrealistic expectations for this new sensor. But in most image settings, even low light, the improvement is noticeable but subtle. That speaks more for the outstanding quality and low-light sensitivity of the D5000 sensor (which is shared with the D90) than it speaks against the D5100. With the D5100 you get higher resolution for improved cropping, and the 14-bit RAW images offer greater dynamic range for more flexibility after the shot is taken.
Speaking of RAW format, as with any new camera, there is a bit of a wait until updates are available for your favorite camera software. As of May 18th, Adobe, Apple, and Nikon have added support for the D5100 RAW files, so you can use Aperture, iPhoto, Nikon View NX2 (v2.1.1 and later), Nikon Capture NX2 (v2.2.7 and later), Lightroom 3 or Photoshop CS5 (via Adobe Camera RAW 6.4 or later). If you use other photo software or another platform, you may want to verify RAW support for the D5100.
Compared to my D5000, Nikon has gone back and addressed most of my concerns on ergonomics and performance:
- camera body is roughly 10% smaller and 10% lighter
- 16.2 megapixel CMOS DX-format image sensor (shared with D7000) captures 14-bit RAW images and offers +1fs greater low-light sensitivity
- ISO 100-6400 range with expansion to 25,600 ISO (D5000 minimum is 200 and expansion to 12,300)
- high resolution (920k pixel) display for greater detail in image previews (although I had to bump up the default brightness one notch for accuracy)
- side-mounted articulating display no longer interferes with tripod (the D5000 display is inconveniently hinged at the bottom)
- dramatically improved (now usable!) LiveView mode with continuous autofocus even in HD video mode (more on that later)
- full HD 1080p movie capture without the "jelly effect", in more standard H.264 mode up to 22 min (D5000 is AVI format 720p up to 5min)
- slightly better control position (LiveView is now a rocker switch on the mode dial, Video Record is just behind and to the left of the shutter release)
- significantly quieter shutter release (plus, a "Quiet Mode" is available although hardly necessary)
- faster performance (4 frames per second)
- SDXC compliant supports higher capacity cards
- remote control sensor on rear now in addition to front-mounted sensor
- improved battery life, and an improved battery release
- battery charger now has built-in collapsable plug instead of requiring separate power cord
- MUCH better eyecap design no longer comes off in my small Nikon camera bag; also an improved diopter (eyeglass) control
- additional in-camera editing capabilities, including ability to trim video
- new "gimmick" special effects: in-camera HDR, selective color, night vision, etc
Let's start with the display - moving the hinge to the side not only makes the articulating display usable with a tripod, it makes the camera body shorter, so that it matches the height of most popular Nikon DX-format lenses and no longer leans forward when set down on a table as the D5000 did. It makes a surprising improvement in shooting comfort also. Nikon has improved the rubberized grip of the body and the thumb rest in the rear, although some have said that the grip is a bit shallow for larger hands. For my average-sized hands it is very comfortable.
The improved control placement is mostly welcome as well. LiveView is now a spring-release rocker on the side of the Mode Dial (VERY handy) and the video record button is also now on the top of the body, in front of the mode dial and behind the shutter release. What I didn't care for is the placement of the rear camera buttons, which now all shift above and to the right of the display to accommodate the left-mount hinge. What I don't like is that the "i" button (used to display and change shooting info) is too far away from the 4-way mode switch, so changing default shooting settings is a bit more of a stretch on my thumb. On playback, the delete button is just to the right of the Zoom buttons, instead of being far away like it should be. I didn't find myself accidentally deleting photos, but I'd rather have had a button closer by that I use more frequently (like the Menu button?)
What has dramatically improved from the D5000 is LiveView performance and HD video capture. Neither are perfect, but compared to my D5000 both are quite usable in the D5100. In LiveView mode, the D5100 tracks faces and subjects quickly and accurately, although still nowhere near fast enough for sports events or that "quick shot" like you might be used to with a compact camera. On my D5100, LiveView autofocus typically took half a second in lower-light conditions, which is no match for the viewfinder, but a huge improvement from the D5000.
Video capture is another notable improvement in the D5100, capturing single videos up to 22 minutes of 1080p HD (if you have the SD card capacity), in H.264 format, with continuous autofocus. Gone is the "jelly effect" of the D5000 when you quickly panned horizontally and the video appeared to bend. In theory, the continuous autofocus sounds like a great improvement for video capture, but in practice I found it slow to react (especially in low-light situations). Too often I found the camera "searching" for the correct focus, even with the (optional) Nikon 35mm F1.8 AF-S lens. It was so distracting that I ended up disabling autofocus and learning how to manually adjust focus as I moved from subject to subject. Also disappointing is that like the D5000, the built-in microphone is monoral. For stereo sound, you must buy the (forthcoming) ME-1 external microphone. Overall, the video capabilities are promising, especially at 1080p, but I am more satisfied with the native 720pHD stereo video captured from my Canon S95.
Rounding out the list of improvements and new features of the D5100 are the new "special effects", including the first in-camera HDR mode for any Nikon D-SLR. In practice, while there may be edge cases for these effects, I am not particularly impressed with any of them, including HDR. First of all, you cannot capture RAW with any of the effects. For HDR, there are further limitations (can only be used in P-S-A-M modes, not auto, no flash, etc). When you can get HDR mode to work, it can only be enabled one shot at a time, and then you have to go back to the menus to turn it on. Luckily, you can assign HDR mode to the Fn menu button. HDR mode takes two quick shots for each shutter press and then combines them in-camera to create a single JPEG. You can specify the exposure difference (Auto, 1EV, 2EV, 3EV) and level of "smoothing" (Low, Normal, High) between the captured images. I took a number of high-contrast shots with HDR enabled and honestly couldn't see a difference, although I'm still going to try. If there is any good news, it's that Nikon has chosen a fairly conservative / realistic HDR algorithm as opposed to an "eye-popping" but over-processed result.
In summary, I'm quite happy with the D5100. It provides the optimal balance of top image quality (even in low light), lightweight and compact (for a D-SLR) body, articulating display (the only D-SLR from Nikon to have this), and HD video (not perfect) that can leverage the outstanding collection of Nikon lenses (understanding that only AF-S lenses will autofocus).
Notable comparison with the higher-end D7000:
- same 16.2megapixel image sensor with 14-bit RAW image capture for outstanding dynamic range, low-light performance, and detail
- ruggedized plastic body lacks weather seal (it's also smaller and lighter weight)
- no builtin focus motor for older lenses (you'll need to buy an AF-S lens if you want autofocus)
- fewer autofocus zones (11 vs 39) and lower-resolution matrix meter
- pentamirror viewfinder (smaller, not as bright, 95% coverage) vs pentaprism viewfinder (100% coverage)
- no flash commander mode (unless you buy an external flash with TTL triggering)
- slower continuous performance (4 vs 6fps)
- 1 SD card slot instead of 2
- no top-mounted LCD display
- fewer dedicated controls for advanced settings (you must use the menu system more frequently)
Notable comparison with the lower-end D3100:
- higher resolution 16.2megapixel sensor with 14-bit depth
- high resolution (920k pixel vs 230k) display, articulating for hard- to-view shots
- higher low-light sensitivity
- faster performance (4fps vs 3fps)
- better battery performance (660 vs 550 images on the same EN-EL14 battery
- slightly larger and heavier body