Extra note on calibrating lightmeters

Something a lot of people struggle with when calibrating the light meter is the calibration… on this blog I have a special selection on light meters (check it out :-)).
When I teach my students to calibrate the meter to the camera I always use an 18% gray card and shoot this in a as flat as possible light situation and make sure that in the workflow I use the values for this card are 128.128.128

 

Here is where the confusion starts.
Some cameras are calibrated different, cameras use reflective metering and are set in values between 12-18% gray. Meaning that some cameras will yield different exposures, which can be compensated. A lot of this has to do with the gamma curves and different colorspaces. For example when we look at LAB a gamma curve of around 2.47 will Yield a 128.128.128 value, but mostly gammas of 1.8 and 2.2 are used in colorspaces like sRGB and ProPhotoRGB.

 

So how do I get to the 128.128.128 values….
Well what you have to remember is that we’re not looking at the way the meter works, the camera works etc. We’re trying to get perfect exposures for the workflow we are using. In other words in MY opinion when I shoot an 18% graycard with my meter, in my workflow, in the colorspace I use, the values should be rendered as 128.128.128

 

This is all we do while calibrating the meter to the camera/ISO/lens combination.

 

I’ve used this technique for many years now and get my exposures within perfect every time, when I calibrate to the technical 119.119.119 or even 110.110.110 the exposures are off and I have to use the exposure slider in Photoshop in every shot. in fact that is also not a surprise because we are now not taking into account the settings in our RAW developer, our workflow etc.

 

It can be incredibly confusing but if we just forget all the technical data and all the voodoo surrounding it, and just look at what should 18% gray be rendered at, I feel that it should be 128.128.128 in my FINAL image.

 

Seeing the fact that even in that aspect there is a huge difference in opinions only shows how open for discussion this topic can be, I always tell people “do what works for you” for me making sure the 18% gray card renders 128.128.128 in my FINAL image makes my exposures spot on in every situation.

 

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