Originally posted by rawr The Leica S2 goes up to just 1250 ISO. The Mamiya DM40 only goes to ISO 800. Why such low-ISO headroom?
Surely that restricts these [ridiculously expensive] beasts just to the studio?
IMHO, the "low ISO headroom" leads to confusion and nothing else.
In reality, these "studio" cameras beat every high ISO monster you can come up with. In both noise and dynamic range.
Compare the best of league for MF, FF and APS-C (Phase One P65+, Nikon D3x, Nikon D5000/Pentax K-x) on
DxO (click onto "SNR 18%", and then "Print" in the upper left corner of the chart).
You'll see that what is called ISO 800 on the MF is more like and performs like ISO 400.
You'll see that the MF camera stops at ISO 800 and uses an "extended" setting for ISO 1600 and 3200 where 4 pixels are binned into 1 pixel (Phase One's Sensor+ patent).
You'll see that the Sensor+ patent has no positive effect as is does nothing else as you would do when downsampling to 50% size in postprocessing.
You'll see that push-processing the MF camera to true ISO 6400 (underexpose 2 stops and pushprocess 2 stops) yields the same low light performance as the best FF in its class and considerably better than APS-C can do.
You'll see that the full theoretical advantage of (uncropped) MF over FF (which is 1.4 stops or 4.2 dB) is not delivered. But a fraction of it is.
To summarize: MF cameras have equal or better low light capabilities than Full Frame and better than APS-C. But MF cameras are build to render high pixel count resolutions. This advantage goes away with high ISO settings which is why MF shooters don't typically care about high ISO. So, the ISO stops where it can still beat FF in terms of effective resolution.