While I was messing around with my camera, I came across an interesting problem in photography. What happens if you take a picture of a white cat in the middle of a snowfield or, for that matter, a black cat in the middle of a coal mine? Well, if you use an automatic camera, you are going to get a rather gray picture. You see, the camera figures that an average exposure of a scene is 18%. This is the middle of a geometric scale between black and white. And who says that your camera’s 18% is really 18%?

The first picture is a white sheet in bright daylight. Or, it is at least what the camera took of it. Adobe Photoshop tells me that the average values for this picture are around 140,140,140.

This time, I stick an 18% gray card in front of the scene and tell to camera to lock onto that value with its meter by using the “AE Lock Feature” (with the FEL button (Flash Exposure Lock)). It got closer, with average values of 230,230,230, but still not in the ballpark.

I finally switched the metering to “spot metering”, metered the scene, and then changed the exposure compensation until the bar was at the top of the graph. It got much closer this time with values around 247,247,247. 8 off. Which is close enough for today’s exercise. Who says the paper was perfectly white anyways?