What is SBR or Subject Brightness range? It is the difference in terms of stops between the darkest and brightest part of a scene. Another way to put it is that is the contrast range of a scene.
Determining the SBR is crucial under certain situations. This is because if the SBR is too great, details within the scene will either be too bright or too dark. Typically, the SBR should be 5 stops or less, in order for the details to be retained.
Using Grey cards for light metering is a photography technique.
Typically, light meters are calibrated for mid-tone meter readings. This mid-tone reading is actually 18 % grey. A grey card is simply a piece of card that is 18% grey in colour.
In the absence of midtone in the scene, a grey card can be used to assess and capture the meter reading.
You can do so by simply placing the grey card in front of the subject for it to be used as a midtone.
In the absense of a grey card, the palm can be used as a midtone substitute. However, the palm is usually 1 stop brighter than 18% grey or midtone. Because of that, you will need to adjust (open) the camera’s meter reading by 1 stop.
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