The difficulty in getting maximum quality out of the Pentax 645D sensor is accurate focus. To that end, I acquired (at no small expense) the Zeiss Victory 3X loupe, Zeiss part number 522012, with the hope that the 3X magnification would solve the focus accuracy issue for manual focusing. You might be able to find a used Pentax 2X magnifier, but I deem 3X barely enough, so good luck.
Of course, any camera with a Live View feature is inherently superior for focus accuracy, yet a CCD-sensor camera cannot offer Live View. There is no substitute for Live View, and it’s high time medium format digital cut the crap, dropped CCD, and designed cameras with Live View so that the claimed resolution can actually be delivered.
To use the loupe, first focus it on the ground glass; it’s enough magnification that the fine concentric rings etched into the ground glass can be seen when focused; these cannot be seen with the naked eye. I focused the loupe on these etched marks. I also tried focusing it on the black guide lines, I observed no difference in my results. The point is that the loupe is not to be focused on the subject, but on the groundglass.
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