Rob Gruhl shot this photo with a 12-24mm 'DX' lens geared for small-frame Nikon cameras mounted to a full-frame 'FX' camera, the new D3. The DX lens is designed to shed light only on a small-frame image circle, but the D3 can be set to record on its entire sensor frame. This shot, taken at a focal length of 12mm, shows the portion illuminated with the DX lens.(Credit: Rob Gruhl)
Canon beat Nikon to market by years with a high-end digital SLR whose image sensor is the size of a full frame of 35mm film. But while Nikon may have been late to the party with its new D3, I think it employed a much smarter approach to a lens compatibility issue.
One of the chief merits of single-lens reflex (SLR) cameras is their ability to accommodate multiple lenses, letting photographers adapt the same camera body to shoot everything from faraway birds to the confined quarters of a small house. It's annoying that one company's lenses generally don't work on another company's camera bodies, but it's even more annoying when a single company's products are incompatible, and the full-frame trend in higher-end cameras has put the spotlight on the issue.
Here's the background. The vast majority of digital SLRs sold today use smaller image sensors measuring roughly 24x16mm that are much less expensive to manufacture than full-frame 36x24mm sensors. Canon and Nikon both have made lenses specifically for these smaller sensors; Canon's small-frame lenses bear the EF-S label and Nikon's are called DX.
One big reason to make small-frame lenses is that wide-angle lenses need to be reworked for small sensors. For example, you need to use a 10mm lens on a small-frame Canon camera such as an EOS 40D to get the same field of view as a 16mm lens on a full-frame camera model such as an EOS 5D. Another big reason is that lenses for smaller sensors can be made smaller and lighter.
For many folks with digital SLRs, having a separate line of lenses for small-frame cameras isn't a big deal. They'll buy a lower-end, small-frame camera, and if they buy a later model, there's a good chance it'll be another small-frame model and their lenses will work fine. But for photographers upgrading to a full-frame camera, the lens compatibility issue rears its ugly head.
Canon shooters can't use small-frame EF-S lenses on full-frame cameras. Full-frame cameras physically can only accommodate EF lenses. Nikon, though, permits its small-frame DX lenses to be mounted on its full-frame FX cameras.
Nikon's approach isn't all smooth sailing. DX lenses are designed to shine light only a small sensor, so by default, a full-frame camera will use only the central portion of the larger sensor, meaning that many pixels are wasted. On the 12.1-megapixel D3, you only get a 5.1 megapixel image. And if you do enable the full sensor to work, in many situations light will only fall on the central pixels anyway, leaving a clear record of the lens' smaller image circle. (The DX-on-FX photo by D3 owner Rob Gruhl above illustrates the effect.)
Nikon's strategy meant that lens compatibility is a bigger issue for professional-level photographers. Its first full-frame camera, the $5,000 D3, has only just hit the market in recent weeks. That means pro-level photographers who wanted to go digital had to invest in small-frame lenses for earlier pro-level SLR such as Nikon's D2Xs. Perhaps from this point forward, a new D3 owner will only buy full-frame lenses, but many already have invested in expensive lenses.
In addition to the relatively inexpensive "kit" lenses that ship with lower-end SLRs, Nikon DX models include a $900 12-24mm f/4 wide-angle zoom, a $1,200 17-55mm f/2.8, a $600 10.5mm f/2.8mm fisheye, and a $700 image-stabilized 18-200mm f/3.5-5.6 super-zoom that's the company's best-selling lens ever.
Canon, on the other hand, introduced full-frame cameras many years earlier--2002 with the EOS-1Ds--meaning pros weren't as far along in their transition from film to digital and hadn't necessarily invested in a lot of EF-S lenses.
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