Originally posted by MNCurt-K10D From a couple of posts here and there, I've gotten the impression that if I shoot an image of a standard 18% Gray card the resulting histogram should peak at the center if everything is working properly. Can anyone confirm this to be the case, in theory? I'm talking about standard, open-aperture metering with a DA or FA lens. I did a quick-and-dirty check with my FA 50/1.4 and FA 100/3.5, and while the 50/1.4 seemed to deliver centered histograms over a wide range of Av settings, the 100/3.5 seemed to wander around a bit more. Before going any further, I wanted to make sure that in fact a centered histogram is the corrected 'expected' result from a gray card image. I also assume that the metering mode (spot, center weighted or matrix) should not matter if the gray card completely fills the image - again, am I off base on that? Thanks for any input or guidance!
Curt
The peak should be at 110 on the luminous histogram, left of center.
Digital Imaging: Essential Skills - Google Book Search
See p 66. I get tired posting all the same links re: meter calibration.
Re: Using a 113 gray standard in digital photo
Or these:...............
A middle visual gray (L* = 50) has these equivalents:
Reflectance = 18.419%
Density = 0.73474
Pixel value for gamma 2.2 (e.g. Adobe RGB) = 118
Pixel value for gamma 1.8 (e.g. ProPhoto) = 100
A true 18% gray card (18% reflectance) has these equivalents:
L* = 49.496
Density = 0.74473
Pixel value for gamma 2.2 (e.g. Adobe RGB) = 117
....................................
118..110 oh well close enough... it's not 127 (which is the center.... 40 "points" to a stop in the center of the histogram (roughly), edges get more logrithmic so it doesn't work the same way.)
Pixel value for gamma 1.8 (e.g. ProPhoto) = 98