As a follow-up to Doug Brown's Exposure Quiz, I photographed two frame-filling images, one white and one black. I used both aperture priority and full auto with no exposure compensation of any kind. The images posted here were shot in the auto mode with a Canon Rbel XTi and the Canon 50mm 1.8 lens; f4.0, 1/4000; ISO 200 in bright sunlight.
The black object is the first image and as you can see, it looks more gray than black and the logo writing is, in reality, dark grey while the welting is more of a light to medium grey, but definitely not white.
Not sure how to post a second image but will see what I can do to get the white object here, also.
Thanks for playing along with my little 'experiment' Katie! It's actually an important lesson in exposure. When you meter a scene, the camera's meter measures reflected light from the scene. The camera is calibrated to define whatever it is that you're metering as the light reflected off of an 18% luminance neutral tone subject. All colors have 18% neutral tones in their tonal range. That means if you meter a white subject, the camera will make it look neutral (in brightness only- we're not talking about color here). The same holds true when you meter an all black subject. The result for white and black subjects is the same; they appear gray. We use exposure compensation to correct for this problem, adding light (or positive exposure compensation) when we meter a white subject to make the whites look white, and subtracting light to make black subjects look appropriately black.
It's a little counter-intuitive, because most photographers are accustomed to dialing in a little negative exposure compensation to keep the whites from getting blown. But in my photo from yesterday, I spot metered a white bird; my spot was completely filled with white. If I hadn't added + EC, my snowy egret would have looked like a gray egret!
Theorectically, if you take a photo of a pure black object and another of a pure white object. basing your exposure on measuring the exposure reading of the reflected light from the objects, the objects in both photos will look the same, i.e., both will appear in 18% grey. But I think in reality, the black will still look darker and the white will look brighter.
Agree with Gail - thank you Katie and Doug! I'm going to go and try this on some swans - if it ever stops raining, that is...:(:(
Doug, will this only work if you spot meter, or does it work for evaluative metering as well?
Regards,
Nicki
Good question Nicki! It works with all types of metering, but you need to understand what portion of the image is being analyzed for each metering mode in your camera. If your swan occupies a small portion of the metered area and the BG is dark, then negative EC is in order to keep the whites from getting blown. In my photo the white of the bird filled the entire area that was being metered.
Exposure homework for Doug
