Focal lengths in portraits

DIFFERENT FOCAL LENGTHS
Here we've shot the same picture using increasing focal lengths to show what happens and how to avoid the problems. One thing to note when shooting digitally, is that the effective focal length of the lens is extended because the middle part of the lens image (unless using a specific digital lens) is captured, and that is effectively further away in the scene being captured. Thus the standard 50mm portrait lens, on a digital camera, gives a field of view and reach of a 75mm lens.

Shooting at 25mm
The prime reason for using a wide angle lens is when there isn't much room so you need the wide angle lens to get the subject into the shot. The problem then is one of massive distortion of the image. This shot was taken at 25mm and results in the head bulging and becoming larger, while foreshortening the rest of the image. It is highly unflattering - look at the horizontal stripes on the top.

The solution is to move back and use a longer lens, but if that really isn't possible, then there is a partial solution. Instead of standing at normal height and shooting at the head, bend down and focus on the midriff. This will elongate the head, but at least it won't bulge and the picture will appear more natural. It isn't great, but it's better than shooting it from head height.

Shoot at 50mm
The human eye is reckoned to have a roughly equivalent field of view as a 50mm lens, hence its use as a portrait lens. This will hugely reduce the amount of distortion in the picture, but if you are quite close to the subject, or part of their body is in front of the torso, then you will still get distortion. It's a big improvement on the last shot mind but the lines on the top still curve, it's still a little top heavy.

Shoot at 75mm
Of course, if you put a 50mm portrait lens on a digital camera then you get a 75mm effective focal length which is the case here. Now the body isn't distorted and looks far more natural. The lines on the top are much straighter. Again though, if close to the subject, or an arm is extended, then that will distort. If the subject is relatively flat to the camera, then this is fine.

Shoot at 150mm
If you want the subject to move around, have parts of the body nearer the camera, then you need to go for a longer lens. It's no co-incidence that a lot of top portrait pros swear by using a longer lens, up to 200mm. The other result of using a fairly long lens is that the field of view narrows right down, so it will exclude more of the background. It also results in a shallower depth-of-field at the same aperture, which is very much worth having if shooting on location. Certainly at this focal length, there won't be any distortion, but you will need twice the amount of room.

Shoot at 300mm
The primary reason for going longer is to get a close up shot of the head and shoulders, without any distortion. It will also ensure that the background, even with an aperture of f/9 which was used here, immediately goes out of focus even if its only a meter behind the subject.

CREATIVE EFFECT
Now, once you understand what a wide angle lens, that short focal length, is going to do to your pictures, you can begin to exploit it for creative effect. The first trick is to deliberately move part of the subject close to the lens, which will cause it to appear massively larger. That's what we've done in the first shot, getting the subject to raise a hand in a stop sign. The hand now appears larger than her head! The classic use for the wide angle lens is to stand on a chair and get above the subject. Now the distortion makes them look like they are a rocket zooming up. Anything at the top of the image will be huge, leading down to a pair of tiny feet.

More flattering uses of the wide angle effect include elongating the legs. Get the subject to sit down, and point the legs diagonally towards the camera. They will now appear much longer, though remember to try to point the toes or you'll get a big shot of dirty soles. Equally, if you adopt a low position, get the subject to place one leg in front of the other and shoot upwards, the legs will appear longer in comparison to the torso and head. The only disadvantage of this is that some subjects don't look good if you are shooting from beneath chin level.

PUTTING IT INTO PRACTICE
Here are three shots showing the principles in action, starting with using a 50mm lens, giving an effective 75mm focal length, at close quarters.