Ok, so you have this wonderful dog with wonderful white fur like snow or the black cat shining like a jewelry piece. Naturally you want to make beautiful pictures of your pet. But every time you try this, it results in very dark or very bright pictures which are far from being pleasing to the eye. So what is the reason behind it and how can you prevent it?
Your camera has evaluative metering as a default setting. So it measures the whole scene and tries to create an 18 % gray over the entire image. When your black dog or cat is making the large portion of your image, your camera will think it is too dark and will try to compensate it by making the scene much brighter. In the case of a white animal, the whole situation is vice versa and you get very dark images.
If you are using an automatic mode like shutter or aperture priority, try spot metering over the fur of your animal and adjust your exposure with exposure compensation. But the best way to take control of the situation is using the manual mode while spot metering over the fur and adjusting your aperture value or shutter speed.
Try one of these methods and hopefully you will get nice shots of your pet.
Deniz L.