As I wrote in Part I of this post, below, it seems to have become a "forum truism" that the 4/3rds sensor size (13 x 17.3 mm) is woefully inadequate and can't compete with the allegedly more desirable APS-C sensor size (14.8 x 22.2 in Canon cameras). I made the argument that assertions for the superiority of the larger size were dependent on direct, controlled comparisons, and that any differences are actually probably too small in magnitude to reliably detect if people were simply looking at pictures.
Readers commented that not all visible differences can be attributed to sensor size alone—implementation and sensor design have a lot to do with it too.
That's certainly true, and to demonstrate it you only have to look at sensor design and implementation with a time dimension. In the year 2000, Canon introduced the landmark D30 (n.b.: not the 30D, a more recent descendant), a camera that was remarkable for any number of reasons. It was the first all-Canon DSLR, and the first to use a CMOS sensor. At 1.6 pounds it was considered almost amazingly compact and light for a DSLR, and, by the time it was reviewed there, Steve's Digicams said, brightly, "With an estimated street price now less than $2600, D30 sales have been and continue to be brisk!" Michael Reichmann made his bones by famously proclaiming that the D30's image quality matched that of film.
The D30 caused tremendous, almost unprecedented excitement at the time. Photographers had been accustomed to a sleepy, saturated market in which progress came mostly as refinements, and most refinements had to do with convenience for the user (rather than image quality) and more efficient manufacturability for the cameramakers. Slow-evolving companies with little R&D could usefully compete alongside companies that made haste somewhat less lazily. In that context, the pell-mell development of DSLRs for several years surrounding the turn of the Millennium seemed like a continuing succession of revolutionary shocks. (It was, among other things, a lot of fun to watch.)
The D30 had 3.25 megapixels. (The "camera to beat" at the time was the 1999 Nikon D1 at 2.74 megapixels, which Digital Photography Review called "Nikons [sic] answer to Kodak's domination of the professional SLR's [sic] market.") You could buy an IBM microdrive card with as much as 1GB of storage, although they were not cheap. Diagonal edges showed visible jaggies at 100%. Regarding noise, dpreview concluded that "Shooting for the web, smallish prints or a family album and [sic] you could certainly get away with ISO 800." It was considered "very fast" because you could take a shot every 1.5 seconds.
Eight years later, we take for granted factorials of two to four, all in our favor, in terms of megapixels, ISOs, shooting speeds, write times, and prices. 1GB flash cards are so cheap they're sometimes given away. The improvements and capabilities of 4/3rds sensors shadow those of APS-C sensors. Digicam sensors routinely exceed the D30's specs—or most of them—and a 4/3rds camera with the D30's specifications would be laughed off the planet.
You don't know
So, anyway, here are a few common assumptions about sensor sizes, closely paraphrased from actual statements I've encountered: "The days of 4/3rds are numbered. It won't be around in a few years." "All else being equal, bigger is always better." "The whole market is now moving to full-frame." "Every advance in quality and capability that is available in 4/3rds is also available to larger sized sensors, so the larger sensors will always be better."
This amounts to "the conventional wisdom" (CW), and it might be correct. (The CW sometimes is.) But ever since I took a debating class in 8th grade it's been part of the repertoire of my thinking processes, so let me just bring up a few "debating points" that perhaps oppose the CW as set out above. Together these don't constitute a coherent argument; you might rather think of them as "nodules" of evidence, little wet balls of fact and assertion zapped at your pretty blackboard diagrams when you're not looking like spitballs through a straw.
Nodule: You don't know. The future isn't always a linear continuation of the assumptions of the past and the present. Progress is not always overtly logical, even if it follows someone's idea of logic. Ten years from now, 4/3rds might be dead. Also, ten years from now, all cameras might have 4/3rds sensors, from pro DSLRs to pocket digicams—at which point such an evolution will be back-constructed to seem logical and inevitable 'twixt here and then. Not saying I know. But you don't either.
Nodule: Despite the public pining of pontificating pundits such as moi demanding small cameras with large sensors, only one is even on the horizon. Is this because tiny sensors the size of fingernails are simply getting so good that Joe Sixpack and Jill Boxed White Wine don't want or need anything more? Is the manufacturers' strategy simply going to be to keep improving the fingernail-sized sensors until people like me have to shut up?
Richard Man (Imagecraft.com), My Wife, Karisu. Olympus E-3 and 35–100mm ƒ/2 lens, shot wide open.
Nodule: Bigger was better when it came to film, too, but that didn't mean that bigger always won out. In fact, film sizes got smaller and smaller until they fetched up against 35mm (24 x 36 mm), at which point there were several concerted attempts, most led by Kodak, to make the sizes smaller still (110, the disc camera, APS), none of which remained viable more than temporarily. So-called medium- and large-format survived, supported mainly by professionals and a loose confederation of aficionados and artists who together comprised an active but numerically minuscule segment of the overall market.
Nodule: "Post-Bayer," as Thom Hogan likes to call it, is going to change the game completely. Don't think for a second that there aren't engineering teams at Canon, Nikon, and elsewhere working feverishly to figure out how post-Bayer is going to play when it hits the mainstream.
Nodule: The market is moving to full-frame, check...based on three extant cameras (Canon 1Ds, Canon 5D, and Nikon D3) and three more (Canon 5D replacement, Sony "flagship," Nikon's competitor to the 5D) supposedly in the pipeline. These will doubtless exploit a market demand that currently does indeed exist. The Sony Mavicas, which wrote directly to CDs, and the digital "bridge" camera, like the Olympus E-10 and Sony F-717, also exploited markets that existed in their time. Where are they now? There's nothing that says any trend has to continue.
Nodule: Film speed. Lens speed. Film grain. Motor drive speed. Shutter speed. What do these and many other technical specifications of photographic devices have in common? I'll tell you: they were once hotly contested fields of competition between manufacturers that were followed avidly by the market...until they reached "points of sufficiency" when further development just seemed to no longer make sense. (Okay, so maybe film speed never really quite got there). Lenses got to ƒ/1.4 and the market pretty much decided that was plenty; faster lenses exist, but they're mainly curiosities that never sold in anything but very low numbers. The Nikon 8008 had a huge market advantage when it came out, with its spectacular 1/8000th top shutter speed and 1/250th flash sync speed; but when faster shutters than that came along, the market pretty much yawned—when you can already freeze moving helicopter blades, you pretty much don't need shutter speeds faster still.
Okay. Fast forward to now, when high ISOs, capture rates and write speeds, shutter lag, resolution, and dynamic range are hotly contested fields of competition between manufacturers that are followed avidly by the market. Will they be forever? Not likely. Much more likely: all parameters will reach "points of sufficiency" where people just won't need or want more. Where those points will be, I can't say. But there's one thing about it that's probably true....
It's not up to you
Idle speculative follow-up question: Let's say (for the sake of argument) that sensors reach this mythical "sufficiency" in every conceivable parameter the market demands by, oh, say, 2015. Then the manufacturers figure out they can develop sensors with the same performance, but smaller, cheaper, and with higher profit margins. Care to guess what your chances of buying a sensor of any particular size are going to be, if there is no demand for such a sensor in the market as a whole and if the manufacturers don't want to make them?
Upshot: Don't write off 4/3rds, and don't assume anybody knows what cameras or digital capture is going to look like fifteen years from now. If the lessons of the last fifteen years would seem to indicate any one thing, it's that this ain't over yet.