In any portrait, you should be wary of what is the 'first point of contact.' I'm talking about what body part is closest to the camera. I'm talking about the subject's body...
Cameras Are 2D
Because cameras create images that are 2D, our 3D bodies are flattened in an photograph. Unlike our eyes that can sense depth - a picture, however, does not give a sense of distance. In an image, we may actually think someone's feet are four inches long... Unless you're in Japan during the 19th century. If you are, then that's weird if you're reading this blog post because of your likely death that happened a while ago.
Closest = Biggest
So, with portraits, we must be careful about what body parts are nearest. We need to understand that what is closest to the camera will appear largest.
If you're not wanting to enlarge someone's knees, don't pose her so her knees are closest to the camera. What's happened with her knees can also happen with thighs, calves, feet, arms, shoulders, hands, backs and butts. I've NEVER had that request..."Hey Eric, could you please make my hips look bigger than they are?" Again, the problem is that the camera is creating images that are 2D. So, we must be very selective in what is closest to the camera.
Fixing Enlarged Body Parts
The fix is to ensure that there isn't any body part that is significantly closer to the camera than another body part. Or, if you have to choose which body parts are furthest from the camera - choose body parts that most of us want to be smaller: hips, butt, stomach, thighs...my super large biceps. These are body parts that look good when they're smaller.
The safest body part to make closest to the camera is the FACE. As humans, we know that bodies come in all shapes and sizes. So, our subconscious brains judge someone's body size by the size of the face. This is why it's a safe bet to ensure that the face is the first point of contact.
Keep Everything Same Distance
Another good way to ensure that you're not distorting parts of someone's body is to make sure that there isn't one part that's much closer to the camera than the rest of the body.
Being Close Makes Distortion Worse
When you're close to your subject, it's very hard to not distort anything. Imagine that your subject is two inches away from your lens. If his nose sticks out one inch from his face, technically, the nose is 50% closer to the camera than his face. It's significantly closer. This means that it would be distorted and would appear much larger than it really is.
If, instead, your subject was twenty feet from the lens, that one inch nose is .4% closer to the camera. .4% isn't significantly different. So, his nose will NOT be distorted in that image. While this is an exaggerated example, the concept is important. Understand that, if you are close to your subject, any body part that is closer will be enlarged. The moral of the story here is, if you're worried about distorting your subject, get farther away and zoom in. Even if your subject's knees are pointed right at the camera, the distortion will be minimized because, as a percentage, her knees won't be significantly closer to the camera than the rest of her body