People and Place. Project 1. Ex. 7. Focal Length and Character.

The effect on the image, if discernable, is not due to the use of different focal length lenses but due to the perspective change brought about by the varying distance of camera to subject.
To maintain a constant image size the focal length of the lens must change if the subject to camera distance changes.

A long focal length will in theory compress the features of the subject whereas a short focal length - a wide angle- lens will exaggerate the perspective and create usually an unwanted distortion. For a head portrait this does not pose a problem until you are uncomfortably close to the subject. In a full length shot the problem of distortion can be more acute. If the subject is sitting or gesturing the subject will have greater depth and the photographer must ensure that the limbs involved do not appear enlarged or distorted by choosing an adequate distance from the camera.
In practice the use of a particular lens will depend at least on one or more of the following issues:                
1)  The space available in the 'studio'. (I would prefer to mount the camera - usually limited by the room size- as far away from the model as possible. If you had the privilige of using a professional model, this wouldn't be a problem.)

2)  The size of the subject - head or full length.
3)  The amount of background you wished to include.
In my examples I have used a manequin head. It has all the features necessary to demonstrate the changes caused by variations in camera to subject distance. Sam - that's her name - is bit short of hair but doesn't figdet. The camera height was set to the centre point of the face and I tried to ensure that both sides of the face were equally in view as the camera was moved towards and away from it.
In my opinion there is little significant change in the image until the distance is approx. 1/2metre (36mm lens equiv. 35 mm film). Here the image change is not due only to change in perspective but also because the camera is so close to the subject that the lens can't see the ears.
Commencing with top image and working down:

1)  Distance 3. 0 metres.  300mm equiv. lens.  Apart from the jaw line

     the face is rectangular.

2)  Distance 2.0 metres.  150 mm equiv. lens.  The face is assumming

     more ovality.

3)  Distance 1.0 metre.   80mm equiv. lens.   Slight triangulation of the

     cheek to jaw. Lip shape subtle change.

4)  Distance 0.5 metre.   40 mm equiv. lens.  Further triangulation of

     jaw to cheek line. Narrowing of forehead. The lip expression has

     changed into a slight smile.