Metering a High Contrast Scene

8/11/2019 Metering a High Contrast Scene

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Scenario 3: metering a high-contrast scene

On page 2, I wrote that there is some combination of shutter speed, aperture size, and imager ISO

that will perfectly expose a grey card in a given amount of light. Thats grey cards. In the realworld there is no such guarantee. !ig " is a perfect example of a high#contrast scene, which

cannotbe perfectly exposed because no current imager can handle the extremes of brightness itincorporates.

High-contrast$ %hen the extremes of brightness in a scene exceeds the capabilities of yourimager there is no ideal exposure and &uite possibly no usable exposure.

!ig ". '2#(2

)otice first that where sunbeams fall on the grass the imager *colour neg film in this case+ hasbeen totally over#exposed, turning the grass white. rass blades are fairly shiny and so act as a

mirror to reflect the intense sunlight into the lens of the camera. This is called specular glareand

is even more of a problem with water, glass, and chrome. Specular glare can sometimes be toneddown to a limited degree by using a polarizer, but otherwise it plays havoc with light meters. -ut

specular glare is not the main problem for metering this scene. bout half of the scene is

extremely bright and the other half of the scene is correspondingly very dar/.
http://daystarvisions.com/Pix/2000-2001ls/42-12.jpg


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!ig (0. Same image showing *+ spot readings and *-+ centre#weighted average reading

t first blush, center#weighted loo/s ideal. One problem is that *as anyone with an older camera

learns from painful experience+ even though the sun and specular glare represent only an off#centre fraction of the scene they will s/ew the reading dramatically toward under#exposure. %e

could use an incident meter but do we read light in the shadows or in the sun1 %e could use aspot meter to read off the grass but where1 )otice that a spot reading off the sun or the

specular glare of the grass will go right off scale. The grass in shadow and the grass in sunlightgive different readings. n evaluative meter will li/ely give a usable reading *probably (23 th+ but

not necessarily the setting you want.

second problem with centre#weighted and incident in high#contrast situations is that therereally is no middle#point or ideal exposure to target for. 4ou will have to sacrifice some

highlights and5or some shadow detail. It really comes down to a matter of 6udgement 7 do you

try to minimize the amount of over#exposure of the lawn, which can be ugly1 Or do you try to

/eep from seriously underexposing the houses and other detail in the shadows1 nd, in fact, if

you are using slide film or shooting 89:s with a digital camera, you dont even try for thisscene 7 any exposure that will /eep the direct sun and specular glare from washing out the entire

frame will result in nothing but in/ blac/ness in the rest of the scene$

!ig ((. Same scene, wrong imager

Slide film or JPEG digital$ the only solution would be to use a tripod and exposure brac/et the

scene by two stops under and over then combine the resulting frames digitallyto merge theproperly exposed bright areas from one frame and the properly exposed shadow areas from

another. This is only do#able if there is no breeze or other sub6ect motion.

Slide and digital photographers have two other tools in their belts to handle high contrast$ neutral

density graduated *); grad+ filters and fill#flash. *)either would have helped to capture !ig ".+

iven neg film or a digital camera with good dynamic range, we can rescue this scene with

careful use of a spot meter.


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(. =eter the brightest area you want to retain detail

2. =eter the dar/est area you want to retain detail

>. If the difference between them does not exceed the dynamic range of your imager, use the

middle value between the two? otherwise choose whether you wish to sacrifice the

highlights or the shadows.

!namic range$ simply means the total range of brightnesses in a scene that an imager canhandle between its blac/ point of total under#exposure and its white point of total over#exposure.

The dynamic range handling@ of neg film varies but is rarely less than " stops. The dynamic

range handling of a digital camera depends upon the physical size of each pixel. s I write this, atypical 9S#sized imager dSAB has about C or " stops, while with digital 89: capture assume D

stops. Slide film has 3 stops ;B *a few exceptions weigh in at 3E stops+. stops is probably a safe assumption for a

dSAB.

Aets put the recipe to use on the scene in !ig ". %e already /now we have no hope of saving the

specular glare areas that go off scale. The rest of the readings range from a brightest of (5(000thsec to a dar/est of (5C thsec, which is G stops. If we are using neg film or shooting raw in digital

we can simply use the median value, about (5"0thsec, but we would do better to do some faster

frames as well in hopes that one would give usable dar/ areas with minimal burn#out. If we areusing slide film, as we see from !ig ((, theres not much hope short of digitally combining

exposures. Still, our best bet for a single frame with slide film would be to drop down 2E stopsfrom our highest reading *(5(000+ for something between (5230 and (5(23, and let the shadowsfall where they may. In practice this means$

Spot-metering recipe " (shortcut for slide#digital in high-contrast light):

(. =eter the brightest area you want to retain detail

2. Set exposure to that value minus the imagers highlight latitude *#2E stops for slide, often

#> stops for digital raw+

>. 9ress shutter release.

!or more detail about recipe 2, including how to determine your cameras highlight latitude for

step 2, see Huic/, ccurate


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@ 9urists distinguish between the dynamic range of the scene and the exposure latitude of the

imager. :xposure latitude is how much of the scenes dynamic range the imager can capture.

=ostly you will hear the term dynamic range being used to cover both concepts.

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Metering a High Contrast Scene