All about exposure: what it is, how to set it up, exposure compensation and bracketing | Articles | Photo, video, optics

Is the pho­to so dark that you can’t see the mod­el? Or is the whole frame so over­ex­posed, as if you pho­tographed a white sheet of paper? All this means that you have the wrong expo­sure.

Expo­sure in pho­tog­ra­phy is the result of how much light hits the cam­er­a’s sen­sor or film in a giv­en amount of time. If there was lit­tle light, then the pic­ture will be too dark — under­ex­posed, and if there is too much, then the scene will be over­ex­posed, that is, over­ex­posed.

We under­stand what expo­sure is, and find out how to set it up and mea­sure it, as well as what para­me­ters in the cam­era set­tings affect it.

In sim­ple terms, expo­sure is also called bright­ness. If the client says that he needs “brighter” pic­tures, raise the set­tings so that the frame is brighter / pixabay.com

How to set the exposure in the camera in manual mode

In man­u­al mode (M for Man­u­al), the pho­tog­ra­ph­er him­self adjusts the basic cam­era set­tings. Expo­sure is affect­ed by three main para­me­ters:

• diaphragm;
• excerpt;
• ISO.

In the era of film pho­tog­ra­phy, expo­sure was adjust­ed using expo­sure cou­pler — a com­bi­na­tion of aper­ture and shut­ter speed set­tings. There you can not influ­ence the ISO — this is a con­stant val­ue that depends on the para­me­ters of the film.

Diaphragm

A para­me­ter that deter­mines how much light will hit the matrix. The amount of light is reg­u­lat­ed by the degree of open­ing of the so-called aper­ture blades. Denot­ed by the let­ter f and a num­ber. For exam­ple, f/1.8, f/5.6. The small­er this num­ber, the wider the aper­ture is opened and the brighter the pho­to will be.

Aper­ture also affects the sharp­ness and depth of field (DOF) — the zone in which objects are depict­ed clear­ly, with­out blur. The larg­er its num­ber, the more areas of the image will be in sharp­ness. That is why the aper­ture is raised for group por­traits (we wrote a guide for you on how to take a group por­trait).

The small­er the aper­ture num­ber, the more pro­nounced the tank and the blurred back­ground. / Pho­to: Eliz­a­beth Chechevic / instagram.com/chechevic_a

A small aper­ture increas­es the chance that the focus will miss, but it cre­ates a beau­ti­ful blur in the back­ground. The pat­tern of this blur is called bokeh. The shape of the bokeh depends on the design of the lens — the more aper­ture blades, the more round­ed the bokeh pat­tern. You can give it any shape your­self (how to do this, read the text).

Excerpt

Con­trols how long light enters the cam­era. This hap­pens due to the fact that the cam­era shut­ter remains open, allow­ing the pho­to­sen­si­tive ele­ment (matrix, film) to col­lect light.

The shut­ter speed is dis­played using a frac­tion­al num­ber (for exam­ple, 1/125, 1/1000) or a “ sym­bol for sec­onds (for exam­ple, 5“ is 5 sec­onds). The low­er the num­ber, the dark­er the frame will be. The more, the brighter.

If the shut­ter speed is long and the cam­era shut­ter is open for a long time, then any move­ment of the hands in the pic­ture will be dis­played as a blur, fuzzi­ness, the so-called “stir­ring”. The fix is ​​sim­ple — fix the cam­era still with a tri­pod and don’t move it until the shut­ter clos­es.

Long expo­sure blur effect / Pho­to: Eliza­ve­ta Chechevit­sa / instagram.com/chechevic_a

Also, slow shut­ter speeds are used for cre­ative shoot­ing — they cre­ate the effect of move­ment or a trail behind an object, draw with light. In addi­tion, a slow shut­ter speed is indis­pens­able for night shoot­ing, when the cam­era needs to col­lect light for a long time in order to pro­duce a pic­ture.

ISO

Shows the sen­si­tiv­i­ty of the matrix to light. In dig­i­tal cam­eras, this func­tion can be influ­enced, but in the pre-dig­i­tal era, ISO remained unchanged and depend­ed on the speed of the film. Dis­played as an inte­ger — 100, 640, 800, etc. The larg­er the num­ber, the brighter the frame.

Too high an ISO val­ue can reduce the qual­i­ty of the pho­to — noise appears on it. At too high an ISO val­ue, there is so much noise that the pic­ture “crum­bles”. There­fore, there is the con­cept of “work­ing ISO” — the lim­it­ing val­ue of ISO, at which noise does not inter­fere. It depends on the capa­bil­i­ties of the cam­era (and, in gen­er­al, its high cost), and can be either 800 or 6400.

By com­bin­ing all three para­me­ters, you can cor­rect­ly expose the pho­to while main­tain­ing max­i­mum qual­i­ty.

Exposure bracketing

Brack­et­ing, or in oth­er words “fork”, allows you to take sev­er­al iden­ti­cal shots with dif­fer­ent set­tings. For exam­ple, three frames: medi­um bright­ness, dark­er and lighter. The same can be done with white bal­ance to get an aver­age shot, cold­er and warmer.

Why do you need exposure bracketing?

• Get three frames with dif­fer­ent bright­ness if you are not sure about the expo­sure set­tings. As a result, there will be sev­er­al pic­tures to choose from, from which you can select the best one.

• Get sev­er­al frames in order to com­bine them lat­er in a graph­ic edi­tor. This is con­ve­nient if there are areas with strong bright­ness dif­fer­ences in one scene. For exam­ple, when shoot­ing land­scapes. So, in one shot, beau­ti­ful clouds will be vis­i­ble in the sky, but the low­er part of the frame will go into a deep shad­ow, while in anoth­er frame the sky will be com­plete­ly white and tex­ture­less, but the grass will be sat­u­rat­ed and detailed. By com­bin­ing these two shots, you get a per­fect­ly exposed pho­to. This is how you expand the dynam­ic range of the image. This effect is called HDR.

Most cam­eras take three shots with brack­et­ing enabled. Some cam­eras allow you to turn on a set­ting that allows you to take up to ten frames with a change in the set­ting in a cer­tain step / Pho­to: Eliza­ve­ta Chechevit­sa / instagram.com/chechevic_a

How to enable exposure bracketing

• Access the menu or look for the Expo­sure Compensation/AEB func­tion on the cam­era dis­play.

• Use the wheel to set the expo­sure spread. This is how the frames will dif­fer in bright­ness from each oth­er. Click OK.

If you are shoot­ing with Nikon, then hold down the BKT but­ton on the cam­era (not all mod­els have it) and set the expo­sure step using the para­me­ter adjust­ment wheel.

• Take three iden­ti­cal frames. The eas­i­est way to do this is in con­tin­u­ous shoot­ing. For more sta­bil­i­ty, you can mount the cam­era on a tri­pod.

How to adjust exposure in automatic camera modes

If you are a begin­ner who is intim­i­dat­ed by the man­u­al mode, do not be dis­cour­aged. In auto­mat­ic and semi-auto­mat­ic modes, it is pos­si­ble to adjust the expo­sure to achieve the opti­mal result. These are modes Tv or S (shut­ter pri­or­i­ty), Av or A (aper­ture pri­or­i­ty) and P (pro­gram).

As a rule, the cam­era itself deter­mines well how to set the set­tings for opti­mal expo­sure. To do this, it mea­sures the bright­ness of the scene, tak­ing the mid-gray areas as a ref­er­ence. It is believed that such areas reflect about ⅕ of the light that hits it, which is equal to the reflectance of 18% (this infor­ma­tion will be need­ed when talk­ing about gray maps for adjust­ing the expo­sure).

Metering modes

For more accu­rate meter­ing and auto­mat­ic expo­sure com­pen­sa­tion, the cam­era can have up to sev­er­al spe­cial modes. Con­sid­er how they dif­fer and in what sit­u­a­tion which one is bet­ter to use.

Average measurement

Eval­u­ates the entire frame, tak­ing into account the bright­ness of all parts of the pic­ture. It is rare in mod­ern cam­eras.

Evaluative (Canon) or matrix (Nikon) metering

It is also some­times referred to as matrix or mul­ti-zone meter­ing. The frame is divid­ed into sev­er­al zones. In each of them, the cam­era mea­sures the expo­sure and adjusts the bright­ness based on the received data.

Eval­u­a­tive or matrix meter­ing is most con­ve­nient if you shoot in auto­mat­ic modes. It is per­fect for land­scape and archi­tec­ture pho­tog­ra­phy / pixabay.com

Center-weighted or center-weighted average metering

Reads data from the entire scene at once, but the main focus is on the cen­ter of the frame. This is log­i­cal, because, accord­ing to the idea, the main object of the scene is often placed in the cen­ter. A detailed analy­sis of the entire scene, as in the case of eval­u­a­tive meter­ing, does not occur. This allows you to use expo­sure com­pen­sa­tion as well (more on that below), as the cam­era does­n’t make auto­mat­ic adjust­ments. Suit­able for reportage and por­trait shoot­ing.

Spot metering

The bright­ness of only a small area of ​​the frame is mea­sured, and all oth­er areas are ignored. This is usu­al­ly the cen­ter of the frame, although many cam­era man­u­fac­tur­ers allow the user to move the expo­sure meter­ing point to anoth­er area of ​​the frame. Use­ful if you are shoot­ing a sub­ject that con­trasts with the back­ground. For exam­ple, a white object on a black back­ground or vice ver­sa. It also per­forms well in stu­dio shoot­ing with back­light.

Partial metering

A kind of dot mode. Also cov­ers a small point in the frame, but larg­er than with spot meter­ing. If spot meter­ing cap­tures about 5% of the frame, then par­tial meter­ing cap­tures about 15%. Suit­able for por­trait pho­tog­ra­phy.

Prob­lems with auto­mat­ic expo­sure arise when there are a lot of too light or too dark objects in the frame. For exam­ple, when shoot­ing in the snow, wed­ding por­traits of a bride in a white dress or a groom in a black suit. In such cas­es, the cam­era thinks that these black and white areas are actu­al­ly a sign that the scene is either too dark or too light. Then the expo­sure may not be set cor­rect­ly. In such cas­es, you can use the expo­sure com­pen­sa­tion func­tion.

Exposure compensation

Expo­sure com­pen­sa­tion or expo­sure com­pen­sa­tion allows the pho­tog­ra­ph­er to man­u­al­ly force the cam­era to light­en or dark­en the frame. To make a pic­ture brighter, you need a pos­i­tive expo­sure com­pen­sa­tion, and to make it dark­er, you need a neg­a­tive expo­sure com­pen­sa­tion.

How to turn on the exposure compensation mode

• Set the cam­era to one of the modes — P, Av (A), Tv (S).
• Select the set­ting on the dis­play — Expo­sure Compensation/Exposure Brack­et­ing Set.
• Move the label. A neg­a­tive val­ue will make the image dark­er, while a pos­i­tive val­ue will make it brighter.

By default, the expo­sure com­pen­sa­tion in the cam­era is adjust­ed with a cer­tain step. A step is a twofold increase or decrease in the amount of light that enters the matrix or film. For exam­ple, for Canon cam­eras, this is ⅓ steps (that is, ⅓ of a step). This is how much lighter or dark­er the pho­to will be after the adjust­ment is applied. In the cam­era menu, you can inde­pen­dent­ly set this step, that is, the dif­fer­ence between each new select­ed num­ber.

Gray Card Exposure Adjustment

The gray card helps to fine-tune the expo­sure, as well as cor­rect the white bal­ance (details on what it is and how to change it can be found in this text).

With the help of a gray card, the cam­era finds an 18% gray object in the scene and under­stands which area to adjust the expo­sure of the entire scene. / Illus­tra­tion: Ans­gar Koreng / wikimedia.org

• Place the gray card in the scene. The more space it takes, the bet­ter. This will avoid mis­takes.
• Set the cam­era to spot meter­ing mode. This is nec­es­sary so that the cam­era mea­sures the bright­ness of a sep­a­rate area, and not the entire scene.
• Take a mea­sure­ment on the gray map.
• Lock expo­sure. Cam­eras from dif­fer­ent man­u­fac­tur­ers may have dif­fer­ent names for this but­ton or func­tion. For exam­ple, Fuji­film has an AEL / AFL but­ton, Nikon has an A AE‑L / AF‑L but­ton, Canon has an AE but­ton, Sony has AEL.

This is espe­cial­ly use­ful when there is a lot of black or white in the frame, when the cam­era may mis­take these col­ors for gray in too dark or too light scenes.