The camera’s built in light meter will give us accurate reading most of the time unless we are exposed to “extreme” light conditions like snow or other highly reflective material like metal in the frame.
These elements can easily fool the camera’s light meter and it is much better to use a gray or white card or even an external light meter to get a more accurate reading.
So here is a tip of what to do if you happen not to have any of those and will get you a reliable white/gray card that you will leave at home.
All you need is to get your hands on a gray/white only once and meter the palm of your hand.
1. Meter your gray card: Let’s suppose that the when metering on the gray card you camera reading is ISO 100, f/4, 1/60
2. Meter the palm of your hand: And make sure to meter the palm, i.e. interior, of your hand. Let’s suppose that the camera’s reading is ISO 100, f/4, 1/100
3. Calculate the exposure compensation: It is easy to notice that there is a 2/3 f-stop difference between the two readings.
Now that you have “calibrated” your palm any time you need it just meter of the palm of your hand and dial in the correct Exposure Compensation calculated in step 3.