If you have an SLR or dSLR camera then chances are, you are wondering which lens to buy, which working focal length to invest in. Well in case you haven’t figured it out yet, the answer is simple (in the sense of choosing your focal length), get what you need for the things you like shooting the most. And please don’t ask about “how X zoom” the lens has, as that is just a marketing trick and means nothing about the lens really. A 70-200mm zoom lens is less useful than a 24mm fixed length if what you like shooting is street scenes, and like wise a 600mm lens is more useful than a 17-85mm zoom lens if you like shooting wild life. If you are still confusing the wide and narrow focal lengths, think of it like this: The higher the mm number, the further away you’ll see. The smaller the number, the closer you’ll be able to see (This is just a way of thinking about it if you are confused, the mm rating means something else in reality!). 200mm is narrower than 24mm because it translates into an angle of view; with a 200mm lens having a narrower view cone than the 24mm.
Another thing that a lens’s focal length changes is the perspective, or how things look. People keep saying that you need a 40-50mm lens. The reason behind it might stem from the fact that it was the lens being given away with cameras most often back when film SLR cameras started popping out or that lenses in that focal range are closer to the human eye in terms of perspective distortion, or rather the lack of it. What do I mean with that is that lenses outside that range tend to change how things look depending on how much wider or narrower the focal length is when compared to the 40-50 range. Check out the old stone olive press.
The reason is that the wider the lens, the closer you can get your subject. But the closer you get, the closer some elements of your subject get to the lens, while the things further away don’t, or at least not in any significant distance. Remember those scenes in comedies where the teacher points at a pupil and the view from the pupil is distorted with the teacher’s finger almost touching the kid’s nose, an elongated arm like a bridge and the teacher almost in the back of the frame? That is what you get when you use a really wide lens and have a subject that is really really close to it. If you go narrower than the 40-50mm range into let’s say 200+, then you get the exact opposite effect. Things get squashed and they lose their extreme depth.
So, remember that when you want to take some portraits. Don’t put up your ultra wide lens and go close to them or they will start complaining about their nose looking like Rudolf. Use a narrower range, like let’s say 70-80 and just take a few steps back if you are too close. (On the other hand, if you are going to take pics of some kids with a sense of humor, you might want to use that ultra wide to make for some wacky perspective.)