Girl Group Portait Photography

Speed-wise, fast lenses (wide aperture) are preferred, as these allow shallow depth of field (blurring the background), which helps isolate the subject from the background and focus attention on them. This is particularly useful in the field, where one does not have a back drop behind the subject, and the background may be distracting. The details of bokeh in the resulting blur are accordingly also a consideration; some lenses, in particular the "DC" (Defocus Control) types by Nikon, are designed to give the photographer control over this aspect, by providing an additional ring acting only on the quality of the bokeh, without influencing the foreground (hence, these are not soft-focus lenses). However, extremely wide apertures are less frequently used, because they have a very shallow depth of field and thus the subject's face will not be completely in focus. Thus, f/1.8 or f/2 is usually the maximum aperture used; f/1.2 or f/1.4 may be used, but the resulting defocus may be considered a special effect – the eyes will be sharp, but the ears and nose will be soft.
Conversely, in environmental portraits, where the subject is shown in their environment, rather than isolated from it, background blur is less desirable and may be undesirable, and wider angle lenses may be used to show more context.
Finally, soft focus (spherical aberration) is sometimes a desired effect, particularly in glamour photography where the "gauzy" look may be considered flattering. The Canon EF 135mm f/2.8 with Softfocus is an example of a lens designed with a controllable amount of soft focus.
Most often a prime lens will be used, both because the zoom is not necessary for posed shots (and primes are lighter, cheaper, faster, and higher quality), and because zoom lenses can introduce highly unflattering geometric distortion (barrel distortion or pincushion distortion). However, zoom lenses may be used, particularly in candid shots or to encourage creative framing.