Pricing. Available from mid-April 2011, the Nikon D5100 retails for a suggested price of US$799.95 body only, or US$899.95 for the body and 18-55mm VR lens.
Compared to: - "For a limited time only..." As dealers clear their shelves to make way for the new EOS-50D, prices on the have plummeted recently, bringing the cost of the 40D down to that of the D90, or even a bit below. (As of this writing in mid-October, 2008, the 40D was available body-only online for as little as $900, almost a hundred dollars less than the D90.) Relative to the 40D, the Nikon D90 offers its HD movie recording capability, contrast-detect autofocus in Live View mode, a couple of extra megapixels, one stop higher maximum ISO, the snazzy viewfinder with on-demand gridlines, its extensive in-camera RAW file processing, the automatic CA correction, and the direct, in-camera support for Nikon's wireless lighting system. On its side of the ledger, though, the EOS-40D offers faster continuous-mode shooting, at 6-6.4 frames/second, depending on the shooting mode, vs 4.5 for the D90. The also has 14-bit internal processing, a PC-type sync terminal for connecting to external flash systems, and full-capability RAW processing software included in the box. The D90 still sports more features, but the 40D's higher continuous-mode shooting speed and 14-bit processing might sway some users in its favor. A closer contest than that with the XSi, but the scales still seem to tip toward the D90. If you find the a compelling bargain, though, our advice is to move fast, as the 40Ds remaining in the market are likely to sell through quickly.
Storage and battery. The Nikon D5100 stores images on an SD/SDHC/SDXC memory card, and is compatible with Eye-Fi cards for wireless connectivity via WiFi. It uses an EN-EL14 lithium-ion battery pack, rated for 660 shots on a charge with 50% of shots using the flash (CIPA rating). No vertical battery grip is available for the Nikon D5100.
Compared to: - The is priced quite a bit below the D90, but in making the Canon/Nikon choice, many people will likely consider it, as it's the closest Canon model on the low side of the D90's price. In this case, though, "closest" means a good $500 or so less expensive than the D90, comparing prices for the kits including lenses. Body-only, as this is being written in mid-October, 2008, the XSi is selling for about $350 less than the D90. (The D60 is the Nikon model closest in price to the XSi.) The XSi and D90 have essentially the same resolution and both have Live View features, but the similarities pretty much end there. Most obviously, the D90 has movie capability. The D90 also shoots faster in continuous mode (4.5 vs 3 frames/second), and goes dramatically higher in ISO (light sensitivity) rating, to a maximum of 6,400 vs 1,600 for the XSi. Then there's the automatic correction for chromatic aberration. Minor details include a significantly higher resolution LCD screen, viewfinder with LCD-based grid that can be turned on and off, extensive in-camera RAW file processing, and direct support for Nikon's wireless flash system. The D90's kit lens also has a significantly longer zoom range. In its favor, the offers a live histogram display in its Live View mode and has 14-bit RAW files and internal processing, which can provide smoother tonal transitions, particularly when processing images from RAW files with heavy exposure adjustment. It also comes with more capable RAW-processing software at no added cost. Any way you slice it though, the D90 delivers dramatically more capability, albeit at a considerably higher price.