The premise, jointly announced earlier this week by Olympus and Panasonic, combines several elements in a way heretofore unknown to digital cameras: a very compact body, a sensor lifted directly from dSLRs, interchangeable lenses, autofocus, and real-time LCD/EVF viewing.
The Four-Thirds consortium evidently looked at their dSLR standard and asked, "What could we do if we dropped the SLR mirror box, pentaprism viewfinder, and 100% telecentric lens requirement, but kept the chip and the lens communications?"
What they could do is thin the camera body by about half and reduce lens-to-chip distance, lens mount diameter, and lens sizes, coining a new system name: Micro Four-Thirds.
The smallest dSLR body is far thicker than the new Micro Four-Thirds standard. Source: four-thirds.org
To place this proposal into context, the smallest Four-Thirds cameras are the smallest and lightest dSLRs ever made: the Olympus E-400, 410, and 420. Yet the Micro Four-Thirds bodies can be less than half the dSLR thickness and likely as not, half the weight. It's not unreasonable to anticipate perhaps six- to eight-ounce bodies and even two- or three-ounce lenses. Equally important, certain body-lens combinations will be pocketable or could at least slip into a small belt case, always at hand. What the photographer-backpacker can expect is dSLR results from a toy-sized camera.
Eliminating the SLR mirror ensures Micro Four-Thirds cameras will be quieter and simpler, and suffer less shutter vibration. Eliminating the optical viewfinder (OVF) means photographers will be relegated to an electronic view finder (EVF) or rear LCD screen, which to date haven't been as easy to use. (Note: zooming rangefinder OVFs exist, but accurate ones are complex and expensive.)
Via an adapter, existing Four-Thirds lenses will work on Micro Four-Thirds bodies, retaining most functions. However, most of the current lenses will dwarf the new cameras.
Micro Four-Thirds bodies will accept existing Four-Thirds SLR lenses via an adapter. Source: four-thirds.org
Changing Chips Alter Design Requirements
Of great importance, if not well understood, is the relaxation of Four-Thirds' rigid telecentric lens standard. CCD imaging chips used in early digicams need light to hit the chip surface at a perpendicular angle, as their photosites sit in depressions that off-angle light can't reach evenly. This creates havoc that the original Four-Thirds standard addressed by demanding system lenses be perpendicular (telecentric). However, newer NMOS chips new used by Olympus and Panasonic don't suffer fatally from angled light, and advanced in-camera processing can address intensity differences that still occur across the frame.
This allows the Micro Four-Thirds rear lens element to sit closer to the chip which, in turn, allows lenses to be smaller. Thus unleashed, camera and lens designers can now employ classic wide angle lens designs unusable in SLRs, create zooms with rear elements that protrude into the camera body, and shrink many lens parts.
Comparison between a Four-Thirds 2x wide angle zoom and an equivalent wide angle full-frame rangefinder prime shows potential size reductions of new standard. Four-Thirds lens is 11-22/2.8 (22-44 equivalent); film lens is 21/2.8. Photo by Rick Dreher.
Other than the system details unveiled this week, we know nothing about actual Micro Four-Thirds cameras-what they look like, how they'll be equipped, what lenses and accessories will be available, when they'll be available, what they'll cost, or how much they'll weigh. We do know they're likely to rely on contrast-detection autofocus rather than phase-detection (as used in dSLRs). Will EVFs be built in or only be a slip-on accessory? We don't know. The new system will allow video-impossible with current dSLRs-and autofocus will likely be contained inside the lens, not the body. We don't know whether image stability is possible and if so, if it will be in-body or lens-based. We also don't know whether Leica and Sigma, current Four-Thirds makers, will issue Micro cameras and lenses. One guarantee: due to "not invented here" syndrome, despite being an open standard, Micro Four-Thirds won't be adopted by big players Canon and Nikon.
Is It Really New?
Only two currently available digital cameras warrant comparison to the Micro Four-Thirds concept: the Leica M8 and the Sigma DP1. The Leica, a classic mechanical rangefinder converted to digital by replacing film with an APS-C chip, uses Leica M-mount lenses dating back to the 1950s and will drain your wallet of about ten thousand dollars once fitted with a couple of lenses. The M8 is significantly larger and heavier than a Micro Four-Thirds camera is likely to be, it also lacks autofocus or, for that matter, any automation other than exposure metering. Far closer in concept, the DP1 is the first compact digicam fitted with an APS-C chip (a rare Foveon chip at that). It has a fixed, prime (non-zoom) lens, and a viewfinder is an optional accessory. It's quite small and light, at about nine ounces, and Ryan Jordan has been putting one through its paces this summer with considerable success. A reasonably complete DP1 kit costs about a thousand dollars. To get an idea of how a Micro Four-Thirds camera might look, take a gander at the DP1 and imagine being able to swap the lens with another anytime you want.
Four-Thirds is an open set of standards that revolve around the Four-Thirds imaging chip that's roughly one-quarter the area of the standard 35mm film frame (18 x 13.5 mm vs. 36 x 24 mm). The vast majority of dSLRs use reduced format chips, and most of those are so-called APS-C chips. Compared to APS-C, Four-Thirds is less wide, slightly less tall, and a bit squarer. In practice, APS-C and Four-Thirds are essentially the same; image differences between cameras using the two arise from chip design and image processing differences, not chip size. By comparison, no compact digicam imaging chip is remotely close in size to Four-Thirds (for example, the 1/2.7" chip used in many compact digicams is 5.3 x 4 mm). So-called full-frame dSLRs do differ considerably, but are not relevant here.