Ray,
good thoughts, with one small disagreement
If the cameras being compared are different formats, then of course aperture, shutter speed and/or ISO should be different.
They should be chosen for each camera as though that were the only camera being used to take the best possible shot of the scene.[a href=\"index.php?act=findpost&pid=159811\"][{POST_SNAPBACK}][/a]
That is the essence of it, and acceptance of this might solve many holy wars between formats. But there is one exception about ISO speed because of this observation:
If the shutter speed is not the same, it doesn't necessarily matter provided both cameras are on a tripod and provided there's no movement in the subject.[a href=\"index.php?act=findpost&pid=159811\"][{POST_SNAPBACK}][/a]
And that means that ISO speed can be the same in this situation, which is probably rather common in medium format work. Or to be precise, ISO speed can be at the optimal value for each camera, which is maybe 50 for ZD, 100 for the E-3.
Of course I expect the Mamiya ZD system to do better in this situation, while the E-3 probably does far better in many hand-held situations, where it can use far lower ISO speed due to in-body IS and such.
For me the most interesting question is
how much better the medium format system is on its natural turf of being able to work at optimal, low ISO speed. I expect better resolution and dynamic range, but for example
- How big do prints have to be before resolution differences are visible and significant?
- How high does the Subject Brightness Range have to be before the DR advantage of the larger format shows a benefit? (Probably most scenes do not have a wide enough SBR for DR considerations to be relevant at low ISO speeds, but of course some scenes do.)
P. S. Quentin: on the subject of DR and SBR, have you tried the E-3's "Auto Gradation", for handling high SBR scenes automatically during in-camera JPEG output? It may be just a lazy alternative to proper tone curve adjustment in RAW conversion, but I am lazy enough sometimes to value good options for getting ready to use JPEGs from the camera.