I responded to a post today in an interesting forum discussion about the new Pentax 645D “medium format” (or, as I prefer to call it, “mini MF” format) digital camera. This is a potentially game-changing camera. I has a 33mm x 44mm 40MP sensor and a body-only price of under $10,000. Its cost is far below that of competing mini MF bodies and a fraction of the cost of recent larger MF systems – and the price isn’t much above that of the high end full frame DSLR systems. While larger is not always better, for some types of photographers this puts a level and type of digital camera performance within reach.

In the discussion forum thread I referred to above, a writer had suggested that the 1.7x size differential between the Pentax 645D and full frame DSLRs would not be significant. In a sense he is right – it will not be significant to most photographers, and I surely cannot imagine why anyone would get one in order to make family photos to post on the web. However, I thought I’d share what I wrote concerning why I think that this might be significant for at least some photographers. My response (slightly edited) follows:

Photosite density is rarely the limiting factor when it comes to maximum print size from DSLR originals. As [the other poster] points out, “technique” stuff tends to be much more critical. Enlargement limits are more likely the result of stuff like camera movement, slight mis-focus, lens issues, etc.

I disagree that the size difference between the 24mm x 36mm full frame DSLR sensor and the 33mm x 44mm “mini MF” sensor isn’t significant. There are several reasons I feel this is the case:

1. From my point of view, the place where “stuff” starts to come apart more easily in a large print from FF DSLRs is in the 24″ x 36″ range or so. I feel that 30″ x 40″ is seriously pushing it for FF DSLRs, though I admit that this is somewhat subjective. However, the 33mm x 44mm 40MP sensor should make this size more realistic – and 30 x 40″ is a sort of standard large print size. (If you don’t print that large, well this isn’t a concern…)
2. To argue that the 1.7x difference between FF and mini MF is not significant would mean also arguing that the 1.6x difference between APS-C and FF is not significant. While I would agree that it isn’t significant for may users who don’t shoot carefully and don’t print large, if your goal is large prints then these are significant differences.
3. Looked at another way, the 33 x 44 sensor size is very close to being two 24 x 36 sensors combined. A very rough way to think about this is that in terms of image to sensor size relationships, you are almost comparing the area of an edge-to-edge 13″ x 19″ print from a 21MP fill frame camera to the area of two 12″ x 18″ 20 MP prints side by side. Or, it is better than stitching a large image from two 21 MP FF exposures.

It is certainly true that the “real MF” digital backs with their considerably larger areas can produce even better results. But let’s take that another step. A good number of former LF (4×5) film photographers have now moved to MF digital systems – but only after convincing themselves (and some are very hard to convince!) that they get results from MF digital that are equivalent to what they were getting from 4×5. Quite a few other photographers have come to believe that FF DSLR images are, in many important ways, equivalent to MF film images. So it is reasonable to expect that the larger 33 x 44 “mini MF” system might be capable of results that are, in many important ways, equivalent to something between MF and 4×5 film quality.

Again, that is not going to be significant to all photographers, and there are practical downsides to the larger formats, too. But I’m encouraged and excited by developments like the Pentax camera – even though it isn’t quite yet what I want, it has the potential to be a game-changer in a bunch of ways.

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