Exposure Compensation


Last week when we talked about taking advantage of your digital cameras histogram I mentioned “Exposure Compensation” and I wanted to explain more about this.  Most casual photographers with compact digital cameras leave their cameras in “automatic” or “program” modes.  We’ll talk more about these modes in future columns.  How the camera works in these modes is by dividing the scene into sections, and reading the light in each section.  Some cameras will have 20-30 sections, while some advanced cameras like Nikon’s D3 will have 1005 sections.  Some will read the light levels as an aggregate, while the more advanced read the light levels present in the three basic colors of red, green, and blue (RGB).  Obviously the more sections it reads and at the most levels, will yield the most accurate results.

How does this compare to the old fashioned light meter your grandfather used to use with his Kodak Brownie?  Light meters would read an entire scene with just one reading, and this reading would be used to set the cameras exposure manually.  We still use light meters today, but mostly in the studio where we’ll measure the light on the nearest cheek of a model, or the most important part of a product, and then we’ll set the exposure by this reading.

Old light meter       Digital light meter


Digital compact cameras in a way are really more advanced light meters.  Many pros use small digital compacts with manual controls and the LCD display to ascertain the best exposure, and then transfer those setting to their medium and large frame film cameras to get the best exposure possible while not wasting film.


A digital camera in program or automatic mode will read the light in the sections of the frame, and then compare those sections of the frame to a database of such readings to help it determine which type of scene it’s exposing for.  This might be a portrait with the person against a bright or dark background, a landscape, or any number of many possibilities.  Once it’s CPU finds a match in the database closest to the scene it’s metering, then it accesses the best settings stored in it’s programs and makes the adjustments for you.  In other words, each time you press the shutter down halfway to autofocus your camera, it’s reading the light in your scene, by sections, comparing this data to a database of such data, and once finding a match it sets your cameras exposure accordingly.  A camera will normally have from 20,000 to 50,000 and more “scenes” in it’s database for comparison.  All this takes place as fast as you can take pictures, which on the fastest DSLR’s can be up to 11 frames per second.  Quite different from your grandfathers light meter!


Exposure Compensation, often abbreviated “EV” merely alters the settings, increasing or decreasing, from whatever settings your camera set for you in program or automatic mode.  EV is something you must set yourself.  On most cameras once set it stays that way until you change the setting, turn your camera off, or some other way so it’s good to read your cameras instruction manual and know how long it holds the setting.  You’ll also need to read the manual to learn how to set EV values.


What is EV good for?  Even though your cameras automatic mode does its best to give you the best exposure, often it’s off by a significant amount.  EV allows you to correct this for the best exposure.  How do you know how much EV and in which direction (increase/decrease) to set?  Your histogram is the best indicator of exposure, and how much EV you need to achieve a perfect exposure.  A histogram is a photographers best friend.  Learning to read it, and adjust EV, is one of the easiest and most effective ways to improve your photography.


You don’t need to change or set the EV for each picture.  If you’re taking a group of portraits in the same location, then you take a single picture using the automatic settings.  Then you check your histogram.  If the histogram shows you need ½ stop of positive EV, then set in ½ stop of positive EV and take another picture.  Examine your histogram.  If the histogram is now showing perfect exposure, then you can continue to shoot pictures at this scene using that same settings, until the scene changes.  Enthusiasts with DSLR (digital single lens reflex) cameras operating in either program, automatic, aperture priority, or shutter priority, will routinely take a picture, check their histogram, and adjust EV for the best exposure, for almost every scene they encounter.  After a while your eyes will do the metering for you and you’ll know if you’ll be setting in negative or positive EV, and soon you’ll be able to accurate estimate how much EV before you even see the histogram.  This is a very important basic skill I make sure the students in my workshops master, and there’s no reason a casual photographer with a much less expensive camera cannot benefit just as much from the same technique.