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Basic Metering in Photography

Basic Meter­ing — Grey card metering

Too many pho­tog­ra­phers rely solely on their camera’s built in light meter to deter­mine expo­sure (F-stop, ISO and shut­ter speed com­bi­na­tion). When they look at their dig­i­tal files, or get their prints back from the photo lab (if they still play with film) they won­der why their prints are not all cor­rectly exposed. To under­stand why this hap­pens it is impor­tant to under­stand the basics of meter­ing and how the cam­era sees and processes information.

Cam­era meters, when used cor­rectly, pro­vide proper expo­sure read­ings which yield a full tonal range on the neg­a­tive or dig­i­tal file.  That said, they can­not think on their own. All reflec­tive light meters, includ­ing your camera’s meter are cal­i­brated to give you an aver­age read­ing of 18% grey (mid­dle grey) on EVERY sin­gle shot. They are designed to aver­age out the light­est and dark­est tones under nor­mal shoot­ing con­di­tions. Most of the time this expo­sure method works well since most scenes have a vari­ety of tones from light to dark which aver­age out to 18% grey. The cam­era meter uses this aver­age to give you a read­ing which records the full tonal range of the scene if your cam­era sen­sor (or type of film you are using) can han­dle this range.

18% grey
18% grey (approx.)

But what hap­pens when there isn’t a wide vari­ety of tones for the cam­era meter to aver­age out? The cam­era aver­ages them out any­way to achieve 18% grey.

IF YOU FILL YOUR VIEWFINDER WITH A TOTALLY WHITE WALL, YOUR CAMERA METER WILL TRY TO AVERAGE THE ENTIRE SCENE (ALL WHITE) AND GIVE YOU BACK A READING FOR 18% GREY. The print made from that neg­a­tive will be grey­ish and might well look like this rectangle. 18% grey

IF YOU FILL YOUR VIEWFINDER WITH A TOTALLY BLACK WALL, YOUR CAMERA METER WILL TRY TO AVERAGE THE ENTIRE SCENE (ALL BLACK) AND GIVE YOU BACK A READING FOR 18% GREY. The print made from that neg­a­tive will be grey­ish and might well look like this rectangle. 18% grey

Know­ing this allows us to com­pen­sate as needed for the cam­era meter’s gen­eral read­ings. The fol­low­ing are good rules of thumb.

If the scene or object to be pho­tographed has pri­mar­ily dark tones DECREASE the cam­era meter’s read­ing by 1–2 stops. (e.g.. brown hair-1 stop, black hair-2 stops) e.g.. from F-5.6 to F-11
If the scene or object to be pho­tographed has pri­mar­ily light tones INCREASE the cam­era meter’s read­ing (open up) by 1–2 stops. (E.g.. blond hair+1 stop, white hair+2 stops) e.g.. from F-8 to F-4

One of the eas­i­est ways to get an accu­rate read­ing in ANY sit­u­a­tion is to take the meter read­ing off a grey card. A grey card is a piece of card­board that is the same tone of grey that your cam­era meter is cal­i­brated for!!!. It can be pur­chased in any pro­fes­sional photo store for about 10 dol­lars or less. By using a proper read­ing off a grey card, you are assured that the cam­era meter is giv­ing you the cor­rect aver­age reading.

In the exam­ple above using the white wall, by plac­ing the grey card in the scene and tak­ing the read­ing off that, the cam­era is bas­ing the expo­sure on the aver­age it was cal­i­brated to mea­sure!!! The white wall (lighter than mid grey) will repro­duce as white. If you throw a sack of coal into the scene, it will repro­duce as black since the whole scene is already based on the aver­age which IS the grey card.

In order to take the grey card read­ing, place the grey card in front of the sub­ject with the grey side fac­ing the cam­era. Approach the grey card look­ing through the camera’s viewfinder until only the grey card is vis­i­ble. This is the read­ing you will use. Back up, recom­pose, dial in the grey card read­ing and shoot. You can also use a reflec­tive light meter on the grey card to obtain the same reading.