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Pentax 645Z: Long Exposures
Very long exposures have traditionally been difficult for medium format cameras, so how does the 645Z perform?
1922 seconds (32 minutes)
Adobe Camera Raw 8.6 (250): ACR settings.
This 1922 seconds exposure (32 minutes) used a 6-stop neutral density filter which tends to deliver yellowish color; the color balance has been seasoned to taste. The image has been pushed by +0.4 stops on top of that very long exposure!
As the RawDigger histogram shows, the blue channel was somewhat underexposed, and the image could have accepted another 1/3 stop or so (see the green channel histogram). The warm light and warm filtration led to the blue-channel underexposure, and this does lead to some shadow noise, but it’s very hard to spot unless one converts into sRGB or AdobeRGB—not a great idea—see Wide Gamut Colorspace Reduces Noise, Avoids Posterization). The noise is almost invisible in ProPhotoRGB.
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Pentax 645 + 90mm f/2.8