Over at pentaxforums.com, there's been a lot of chatter about when Pentax is going to release a full-frame body to compete with Nikon and Canon. With Nikon set to release its second full-frame camera very soon (the D700) and at a price (around $3000) that sounds more like a new computer than a new car, this chatter is likely to increase. To some posters, a Pentax full-frame camera seems necessary, as in, "without it, Pentax will die." To others, it seems inevitable, as in, "Pentax will do it just because everybody else is doing it." To a third group, well, the future is harder to read, in part because the advantages of a full-frame sensor are less obvious, especially in the long-run. I'm in this third group.
Which brings me to an excellent article entitled "Is full frame the coming thing?," by Mike Johnston of the Online Photographer, one of my favorite photographic blogs. I recommend the article. It's not often that you get this much honesty and intelligence on the same web page, and for free.
I have only one comment to add. It seems to me that the main advantage of full-frame sensors is that they produce photos that have less digital noise, especially at higher ISOs. Shallower depth of field isn't an advantage, as far as I can tell, since with an APS-C sensor like the ones in my Pentax DSLRS, I can already get paper-thin depth of field if I want, simply by opening up to f/2.8 or something like that. Back when I was still using a Canon PowerShot S3 IS, I did find it difficult to achieve selective focus. But with my Pentax DSLRs, the problem is seldom too much depth of field: it's too much noise.
Now, what if there's more than one way to reduce noise? There does in fact appear to be more than one way. The Pentax K20D is far less noisy then its predecessor, the K10D. Given identical shooting conditions, the K20D at ISO 1600 produces a photo that's about as noisy as a photo taken at ISO 800 on the K10D. How was this achieved? Well, the sensor in the K20D is a CMOS sensor, and apparently Samsung (the maker of the sensor) managed to design it so that it's simply less noisy. Different and better type of sensor, but same size.
It's pretty clear to me that there are some physical constraints here. Mike Johnston asks, if full frame is better, then why not something even larger? The answer of course is both financial and, sooner or later, physical. Perhaps we'd be taking better photos if we all carried huge large-format boxes around, but obviously, it's awkward to use that sort of camera - one that requires a tripod - for much besides landscapes and formal portraits. A camera has to be small enough to be portable, and large enough to support the necessary controls.
Personally I hope full-frame is a fad. I don't know what my own future will bring, but for every daydream I have about getting a Nikon D3 (or D700), I have an offsetting daydream about getting an Olympus DSLR with its smaller 4/3 sensor and its 2x crop factor.