Exposure Compensation

Expo­sure com­pen­sa­tion allows you to increase or decrease the stan­dard expo­sure set by the cam­era. It’s par­tic­u­lar­ly use­ful when pho­tograph­ing over­ly bright or dark sub­jects, high-con­trast scenes, or in sit­u­a­tions with con­sid­er­able back­light­ing, all of which may deceive the camera’s auto-expo­sure pro­gram­ming to set expo­sure val­ues that mis­rep­re­sent what you saw. White sand beach­es and snows­capes present famil­iar scenes in which cam­eras can set erro­neous expo­sure val­ues. Since these scenes fea­ture high-reflectance sur­faces spread even­ly across the frame of your com­po­si­tion, and because the camera’s reflect­ed-light meter sets expo­sure val­ues to ren­der sub­jects as mid­dle grey, the result­ing pic­tures are typ­i­cal­ly under­ex­posed. Expo­sure com­pen­sa­tion is the fix: it lets you use your bet­ter judge­ment and under­stand­ing of the sub­ject to over­ride the camera’s auto-expo­sure pro­gram­ming in sit­u­a­tions where mis­takes are like­ly.

On most cam­eras, expo­sure com­pen­sa­tion is acti­vat­ed by a ded­i­cat­ed but­ton marked by a square icon fea­tur­ing a black on white + (plus) and a white on black – (minus). Press­ing the but­ton and rotat­ing the appro­pri­ate dial will input the desired lev­el of expo­sure com­pen­sa­tion. (The exact pro­ce­dure is cam­era-spe­cif­ic, so check the user’s guide.) The amount of expo­sure com­pen­sa­tion you set is shown by the posi­tion of the expo­sure lev­el indi­ca­tor or by a num­ber, both rep­re­sent­ing units of EV. In gen­er­al, expo­sure com­pen­sa­tion may be set in incre­ments of ⅓ EV, up to a total devi­a­tion of ±2 to ±5 EV (depend­ing on cam­era mod­el).

Regard­less of your select­ed auto-expo­sure or meter­ing mode, by set­ting expo­sure com­pen­sa­tion to +1 EV, you’re instruct­ing the cam­era that it must increase its auto-expo­sure val­ue by one stop (i.e., one-stop over­ex­po­sure com­pared to the camera’s stan­dard). The process works in the oppo­site direc­tion, too; by set­ting expo­sure com­pen­sa­tion to –2 EV, you’re instruct­ing the cam­era to reduce its auto­mat­i­cal­ly deter­mined expo­sure by two stops (i.e., 2-stop under­ex­po­sure com­pared to the camera’s ide­al).

The para­me­ters adjust­ed by expo­sure com­pen­sa­tion cor­re­spond to your select­ed auto-expo­sure mode. On most cam­eras, expo­sure com­pen­sa­tion is only avail­able in the Pro­gram, Shut­ter Pri­or­i­ty, and Aper­ture Pri­or­i­ty auto-expo­sure modes. In Pro­gram mode, expo­sure com­pen­sa­tion is achieved by adjust­ments to both the shut­ter speed and aper­ture. In Shut­ter Pri­or­i­ty mode, expo­sure com­pen­sa­tion is per­formed by changes to the aper­ture. The cam­era will warn you when your desired lev­el of com­pen­sa­tion requires an aper­ture val­ue beyond what the lens can achieve. In Aper­ture Pri­or­i­ty mode, expo­sure com­pen­sa­tion is made by adjust­ments to the shut­ter speed. The cam­era should warn you when your desired lev­el of neg­a­tive com­pen­sa­tion requires a shut­ter speed that is faster than your camera’s capa­bil­i­ty. Expo­sure Com­pen­sa­tion isn’t avail­able in Man­u­al mode because the shut­ter speed, aper­ture, and ISO are deter­mined by the user, and there’s no auto-expo­sure pro­gram to over­ride.

Exposure compensation and metering modes

Expo­sure com­pen­sa­tion requires the abil­i­ty to antic­i­pate when a camera’s auto-expo­sure pro­gram may lead expo­sures astray, and your choice of meter­ing mode can either assist or hin­der this effort. In gen­er­al, there’s greater uncer­tain­ty in pre­dict­ing the degree of expo­sure com­pen­sa­tion a scene requires when your camera’s meter­ing mode is set to some­thing sophis­ti­cat­ed, such as eval­u­a­tive, matrix, or mul­ti-pat­tern meter­ing because it’s hard to deter­mine to which parts of a scene the cam­era will assign greater promi­nence. The amount of expo­sure com­pen­sa­tion a sub­ject requires is more pre­dictable when the camera’s meter is set to aver­age and cen­tre-weight­ed meter­ing. In either of these modes, you can per­form a quick men­tal analy­sis of the tonal vari­a­tions in the scene, and either defo­cus your eyes or squint them to get a sense of the aver­ages your cam­era will pre­fer and then make the nec­es­sary adjust­ments using your bet­ter judg­ment.

Last­ly, spot meter­ing pro­vides the most accu­rate method of set­ting expo­sure com­pen­sa­tion because it allows you to iso­late a sin­gle tone with­in the com­po­si­tion pre­cise­ly and fix com­pen­sa­tion accord­ing to whether you believe that tone should be exposed brighter or dark­er than mid­dle grey, and by how much (if at all).

Exposure compensation and skin tones

The accu­rate rep­re­sen­ta­tion of skin tone and colour has been the pur­suit of pho­tog­ra­phy for many decades, with most (rel­a­tive­ly) mod­ern con­sumer and pro­fes­sion­al films being spe­cial­ly for­mu­lat­ed to pro­vide both accu­rate and pleas­ing results. Por­traits require par­tic­u­lar atten­tion because peo­ple are acute­ly sen­si­tive to notic­ing slight devi­a­tions from a pre­cise rep­re­sen­ta­tion of skin tone and colour. If the inten­tion of your pho­tog­ra­phy is por­traits of peo­ple fea­tured promi­nent­ly in the frame, then you should con­sid­er tak­ing a spot meter read­ing off the subject’s face to deter­mine what degree of expo­sure com­pen­sa­tion suits them. Auto-expo­sure brack­et­ing could be use­ful in such cir­cum­stances. In gen­er­al, indi­vid­u­als with light and pale skin tones ren­der well with +1/2 to +2/3 EV com­pen­sa­tion, and indi­vid­u­als with dark to very dark skin tones present nice­ly with 0 to –2/3 EV com­pen­sa­tion.

Exposure compensation and auto-exposure lock

There will be cir­cum­stances in which you’re tasked with tak­ing pic­tures of mul­ti­ple sub­jects under the same light­ing. How­ev­er, if the scene con­tains a vari­ety of uneven­ly dis­persed tones, either on your sub­jects or their sur­round­ings, the camera’s auto-expo­sure pro­gram­ming may set wild­ly dif­fer­ent expo­sures val­ues between each pic­ture, despite the con­sis­ten­cy of the inci­dent light. Although cor­rect­ly set­ting expo­sure com­pen­sa­tion for each pho­to can accom­plish con­sis­tent and accu­rate results, the amount of com­pen­sa­tion will change between images, and mak­ing these deci­sions will become tedious. For­tu­nate­ly, there’s a more effi­cient way to han­dle such sit­u­a­tions.

Auto-expo­sure lock, or AE lock, is a fea­ture com­mon to many DSLRs and mir­ror­less cam­eras and allows users to lock the camera’s auto-expo­sure val­ues tem­porar­i­ly. AE lock is use­ful in sit­u­a­tions where you plan on tak­ing pic­tures of var­ied com­po­si­tions or sub­jects under the same light­ing con­di­tions, and in cas­es where the area of focus is dif­fer­ent from the expo­sure meter­ing zone. For a detailed overview of your camera’s imple­men­ta­tion of AE lock, refer to its user’s guide. In gen­er­al, the AE lock func­tions in one of two ways on most cam­eras, either as a press and hold but­ton or as a switch. Press­ing and hold­ing the AE lock but­ton locks the expo­sure to the cur­rent­ly dis­played val­ues for the dura­tion the but­ton is pressed. When used as a switch, the expo­sure is locked when the AE lock but­ton is pressed and released when the but­ton is pressed again (or after the cam­era is pow­ered off and on). When AE lock is used in con­junc­tion with expo­sure com­pen­sa­tion, the camera’s stan­dard auto-expo­sure val­ue is locked, but you may still vary the total expo­sure by adjust­ing expo­sure com­pen­sa­tion.