18% or 12% ?
Q. Why are gray cards still 18% gray whilst meters and camera meters
TTL are 12%’ish gray.
Light meters and in camera meters are calibrated at the factory using ANSI standards.
The standard has always been for a "luminance" value that is roughly
equivalent to the reflectance of 12% gray
18% gray value comes from the print world. On printed material, it’s been stated
that the half way point between black and white reflects 18% of the light, it
has been used for printing and darkroom and continues to be designed for that
this is approximately 1/2 stop difference. If you fill the frame of the
camera with a gray card, that is evenly lit and use the cameras metering
it will not be an accurate 18% gray it will be a 12% so if you are
digital you should shoot one frame of the card and notice that the has a spike
that is slightly to the left of middle, you would need to adjust a 1/2 stop
to get the histogram to be correct in center.
The mass public has been brainwashed into thinking that 18% gray was the correct
exposure setting for film, slides are designed for 12% as cameras are designed
for the same, but through years of market and a lack of real attention to detail
the two have become intertwined and have continued to be a misconception.
I hear that camera companies have stated that they use 18% but the technicians
calibrate it to the correct 12% so even in camera companies own literature they
have made the same mistake, some companies have not stated that and some have
corrected it and some do not list it at all. So that may not be the case
in any specific user manual.