If you are still unsure about getting the correct exposure, there is a cheap but very effective device called an 18% grey card that can limit your frustration, if used correctly.
When light falls upon a certain object; if the object is too dark your camera or meter will automatically give you an over-exposed reading. This also happens when we take a reading from something that is too
bright - the meter gives us an under-exposed reading.
We need to find a mid-tone object for our meters to read the proper exposure.
Sometimes if we are taking pictures in a high contract scene a mid-tone object is impossible to find. 18 % grey is the mid-tone between pure white and pure black.
An 18% grey card will record the exact light that will touch any object. Start by placing the grey card where you are going to take your reading, point your camera or light meter at the grey card - your meter should read the exact light that falls upon the card.
These cards can be used for all types of photography. If you are taking a portrait place the grey card beside the subjects’ face. This will give you an exact reading and help to capture perfect skin tones.
We don’t need to understand the full science of how this works, but knowing a little doesn’t hurt. All light-meters are calibrated to produce an exposure of 18% The grey card reflects the exact same reading.
This card only costs a few Euro, and most decent camera stores should sell them. The 18% grey card should become an important part of your equipment. The grey card can be used if you shoot with digital or film cameras, and whether you use black and white or colour film.