A prime lens is one that has a fixed focal length whereas a zoom lens has a variable focal length. Zoom lenses are popular for the flexibility they afford in different shooting situations, but a prime lens is sometimes the better option. For example, prime lenses almost always have a faster f-stop and this allows them to perform better in low light. Low light situations are one of the most challenging for photographers to work in, so having a prime lens at hand can save the day. Prime lenses are also useful when there are several light sources in the shooting area, such as different lighting fixtures in a dark room. Prime lenses also afford a shallower depth of field and are easier to handle due to their smaller size and weight. Such lenses can require a bit of flexibility without a zoom function but the end results are well worth it, especially in demanding low light situations. With a zoom lens it is easy to "move" the image closer or farther away by turning the lens, with a prime lens you have to "move" your body closer or farther away.

I (Michele) just got a new Nikon D7100 (love it!!!) and bought the 85mm 1:8 prime lens.  My daughter had her graduation breakfast and mass yesterday, and as you can see, I got fabulous results with it. I have always used zoom lenses, and Oliver convinced me to try this lens.  I had to move my body in and out to get closer and farther away, but I love the lens, even inside the dark gym I got great results.  Consider trying a prime lens to add to your collection.