Originally posted by Parallax This is completely subjective on my part, but in my mind medium format has always been anything on a roll that's bigger than 35mm. I've always considered sheet film to be large format.
Even though the same roll is used, it's probably better to think of the different formats by the systems they are loaded in. Technically, yes, a 645 Mamiya, a 6x6 Hasselblad and 6x7 Pentax are all MF, but the way they are used and their output can't really be compared apples-to-apples.
Originally posted by i83N So as pentax finally making FF can we hope for true MF sensor in 645 line? If I recal it 645D and Z sensor (especially D) are just two apc-s sensors put together side by side and true MF is two FF sensors side by side.
Depends on the camera in question, but full-frame (645) MF is considered to be around 40.5 x 56mm. Even if we were to put two 35mm sensors side-by-side, we would "only" have 36x48mm, which is quite a bit smaller. And of course it's not as simple as putting anything "side-by-side", the Sony 51MP sensor is a completely original design that likely doesn't even borrow from the D800 since the pixel pitch is different. Sony does have to use mask stitching to achieve a sensor of this size and resolution, all while maintaining the small production process required for high DR, so it's not easy to manufacture even as it is.
There are only a few companies in the world that actually make computer chips, so Pentax is wholly dependent on Sony (or others) for whether or not anything bigger will come out, but how prepared Pentax is to bet on something another company may or may not do is out the scope of our knowing. For now we can only speculate, but it does seem that Pentax isn't writing the possibility off entirely, since the 645Z is exactly the same size as the D, which is the same size as what a film Pentax would be... unless they plan on putting out a full 645 sensor version, there is no reason why they should have kept the camera this large if they only ever expected to utilize a crop sensor.