[cjbprime]

My understanding is: 1) More megapixels, 2) a larger sensor (more than twice as large) means more signal-to-noise at each pixel site which means less noise in low light, 3) the Mamiya has far greater dynamic range (around one stop greater, double the amount of light).

[Matsta]

You're correct. What I'm wondering is why they used a 1DX instead of a Sony A7S? The ISO range on the Sony would of probably outdone both Canon and the Mamiya.

Taking photos at ISO 409,600 would be pretty awesome IMO.

[fennecfoxen]

You don't really want photos at ISO 409600 per se, though, you just want photos at the lowest ISO that can get you the necessary depth-of-field for your shot (here extended with tilt-shift lens) at whatever shutter speed avoids being too shaky. And then you want as high of a dynamic range of possible, so you can distinguish the brightest brights from the darkest darks in a single shot.

If you can do that already with the sensitivity you've brought, higher ISO doesn't buy you anything...

[jzwinck]

Why use the Canon 1DX? The photographer has a long-standing and public relationship with Canon.

Why not use the Sony A7S? The photographer uses a Canon 200-400mm f/4 lens, and the nearest Sony equivalent is 70-400mm f/4-5.6, which means at the long end it captures only half as much light, instantly negating any possible ISO range advantage offered by the A7S.