OK, first I have to tell you how this photo came to be. My cat is always finding new and interesting places to sleep and it takes me a while to discover them. But recently she would disappear inside the house for a few hours and then come back with her butt and tail all wet. Then, by chance, I found out where she'd been hanging out: she had started sleeping in the bathroom sink, which had a slow drip, which explained the wetness. Turns out she likes the hot water dripping on her!
I was originally going to call this posting "Keep Your Sinks Clean" because after I had shot a few frames of her (she's a very cooperative cat when it comes to photography) I noticed that the sink needed cleaning! So I had to use Photoshop to "clone away" a few dirt spots. But she still sleeps there and I want more photos of her in the sink, so now I keep the sink spotless.
But let's return to photography tips! Because the bathroom is white and there is a big mirror behind the cat, the on-camera flash was getting fooled into underexposing the shots. The camera saw all of that bright light bouncing back and thought (rightfully so) that there was more light than there really was (especially on the cat) and so it as shutting off the flash before it had enough light. The way that TTL (though-the-lens) flash works is that when you take a flash picture, the camera measures the amount of flash actually passing through the lens and hitting the sensor. If the subject is very bright, it shuts it off before the camera actually does have enough light. In this case it was causing the sink to come out gray, not white, and the cat was far too dark.
Remember, all cameras are programmed to produce subjects of a medium gray. So even if you're photographing a white sink, the camera wants to make it gray. Normally, with average-colored subjects, the camera creates a good exposure. But with subjects like a bright beach or white snow--or a white sink--the camera gets fooled.
The solution? If you're using a flash around a very bright background, use your exposure-compensation feature to add an extra stop or stop-and-a-half (experiment to see which works better) of light. I added 1.3 stops of compensation to this shot and it kept the sink white and the cat was almost perfectly exposed. I did have to lighten the cat a bit during editing, but no where near as much as I would have without the compensation.
So, today's lesson: use exposure compensation with flash in bright surroundings--and keep the sink clean!