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EXCERPT page containing first few paragraphs. 2022-08-15 23:35:34

Pentax 645Z

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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Variants RGB, Red, Green, Blue, Gray Gamma 2.2 available in full article
1922 second exposure (32 minutes)
Pentax 645 + 90mm f/2.8

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