I've watched the furor over the matter of the "missing" optical viewfinder (OVF) on the Olympus E-P1—not only here but all over the web—with bemused curiosity. Maybe I just understand camera design a bit more thoroughly than the average bear, but, to me, it was a given from the very first that a Micro 4/3 camera wouldn't have an OVF. At least, not a built-in, all-purpose one. Not a surprise.
It's a case of classic opposing design parameters. My standard example of an opposing design parameter is a sailboat hull. You can have a hull that goes fast through the water, or you can have a hull that holds a lot of cargo. But you can't optimize for both at the same time. The more one parameter is optimized, the more the other is compromised. For a given amount of speed you can try to optimize capacity, and for a given amount of capacity you can try to optimize speed, but to say you want both to be optimized at the same time is oxymoronic, like saying you want long hair but you want it really short.
The situation is a little more complicated in the case of an OVF on a camera, because we're looking at more than just two parameters, but we should at least ascribe the problem to its real cause: the trouble is the popularity of zoom lenses.
Once you decide to provide interchangeable lenses, then you must provide a zoom. Photographers functioned well for 7/8ths of the medium's history without zooms to speak of, but now most people want them, and if a company wants to sell cameras then it has to provide a zoom or zooms. And once the decision is made to provide a zoom lens, then any non-TTL (through the lens) OVF is out. It's not just that a good non-TTL zooming optical finder is difficult to implement, and it's not just that any such finder would be large and expensive. The problem is that the physical bulk of lens gets in the way of the finder's view.
Even on a rangefinder Leica, some of the more recent premium primes are large enough to block a significant portion of the view. The picture above is a quick shot taken with a D700 and 28mm of the view through a Leica M7 .58 viewfinder. The gray bars are the framelines (they're brighter to the eye). Despite the "ventilated" lens hood on the 35mm Summilux ASPH lens, the lens blocks the lower right-hand portion of the field of view. (That strange-looking structure in the yard is a "square foot garden," in case you're wondering. I have a bad back, so I built it up in the air. Keeps the durn rabbits out, too.)
Zooms are bigger than prime lenses, even fast premium Leica primes. Big zoom, small camera? A built-in optical finder in a small or even medium-sized non-TTL camera is going to be blocked by the lens.
So the camera's designers have a couple of choices. They can stick to a single-focal-length fixed lens, in which case an OVF makes good sense. They can stick with a set of moderate primes (i.e., no superwides or super-teles), in which case they can still design a built-in OVF (that's the classic rangefinder solution), although it would be considerably more complicated, and compromises start to enter into it. Or they can dispense with the OVF altogether in favor of an electronic viewfinder (EVF) (this is what the Panasonic G1's designers opted for). Or they can dispense with the built-in OVF and provide a clip-on type suited only for one lens of one focal length (the Oympus E-P1 solution, so far).
But all this garment-rending and teeth-gnashing about the E-P1 not having an OVF is just...misguided. Mistaken. Not gettin' it. Just try imagining it—what is it you want? How would it work? What would the problems be? Try imagining it, and you'll see. You want handling like a Porsche or hauling like a semi? You can't have both at once.
The trouble is that the market as a whole demands its zooms. To murder the old saying about having your cake and eating it too, you can't find the view and zoom it too.