One may be the loneliest number, but it may also be all you need. Gear is necessary for photography. Gear is a huge part of the fun of photography for many photographers. And having a variety of lenses at our disposal allows us to get shots in all kinds of circumstances. But when you're not out shooting for money, and instead are trying out a slowed-down approach to photography for a personal project, one prime lens may do nicely.
Covering All Angles
An ultrawide to capture all of that architectural masterpiece that unfortunately needs to be shot from just a few feet away to avoid getting unsightly signs, cables, cars, or other buildings in the frame as well. A wide reportage lens to go with the flow and make the viewers of out photos feel as if they were right there with us, as if they could step into the image. A normal or short tele lens for somewhat more environmental portraits, a tele for headshots, long tele lenses for sports, or images of animals. These days, most of us opt for zoom lenses. Be it the holy trinity (different lenses depending on whom you ask and what they shoot, but generally a wide angle zoom, like Nikon's 14–24mm or Canon's 16–35mm, a standard zoom such as the ubiquitous 24–70mm lenses, and a short-to-medium tele lens going from about 70 to 200mm), or just one favorite standard zoom.
I do not want to start one of the age-old zooms vs. primes debates or rail the image quality of any one lens here. The differences between a bad zoom and a good prime are much more a question of implementation than they are one of necessary design decisions. Zooms are great. They pull things closer in fractions of a second when needed, and can let you go wider without stepping back. A standard zoom is a miraculous thing. It is almost essential in today's competitive market for photographers trying to cover things like weddings, fashion, or portraiture. A 24–70mm f/2.8 lens will let you do anything from wide-angle landscape or architecture to portrait with blurred-out background. It's a lens in the truest spirit of "be there" photography, that is, a lens that works so well because you don't have to think about which lens to use. It's on your camera and it lets you focus on getting the shot instead of fiddling with multiple bodies or multiple lenses. It's nice and simple that way.
Much has been written about how zooms make photographers lazy because they do not force you think about composition as much, or because you don't have to figure out if you should step back or forward or change lenses. I find myself very skeptical of such overall condemnations. Laziness is a question of mindset as much as it is one of equipment, and some laziness in one aspect of photography can lead to greater creativity in another. What does ring true, however, is the fact that zooms let you see one scene in many different ways. This may lead you to experiment, trying out if the ultra-wide or the tele angle will make for a better image. The fact that you can zoom will make you zoom. Sometimes, however, the fact that the angle is fixed and that you have to work around that fixed angle, will make for more interesting pictures. To challenge yourself this way, you don't need a whole lot.
Constraining Yourself to One Focal Length
This summer I was on a work-related trip to a somewhat drab industrial town in the middle of Germany. Since photography wasn't going to be the main focus, I brought only my iPhone, a Fuji X100s, and an old Nikon F801-S (also known as the N8008) with a 50mm lens. I hardly pulled out my phone and I left the X100s in the hotel room as I explored. As I walked the streets, I kept cursing my limiting choice of one prime lens. I felt like I could never quite get everything in the picture, or like I could not get quite close enough.
It wasn't until weeks later, when I held the developed photographs and looked at the scans, that I realized I liked almost every single image on the few rolls I had shot. The subject matter wasn't exciting, but nonetheless, I genuinely liked the pictures. Concentrating on one focal length had forced me to cut off frames where I would otherwise have attempted to get everything in. This had forced me to think about how exactly I would do that and still make an image that I felt was worthwhile. I had struggled with the 50mm lens. It's still not my first choice, but since 50mm lenses are so plentiful and cheap, they're worth becoming acquainted with. I had come away from the experiment with the knowledge that while often I might want another lens, I maybe shouldn't always have that choice.
It's Got to Be Perfect(ish)
50mm or its equivalent for other sensor sizes, because of many factors having to do with history and economy, is a very popular focal length today. (Actually, most 50mm lenses tend to be a little shorter than that still, usually around 52 or 53mm). There is, however, another and I would argue more versatile choice: the perfect normal lens.
"Perfect normal" is the focal length equivalent to the sensor or film format's diagonal. For a 24x36 full frame sensor, this would be about 43.3mm. The very first film SLR I ever bought, a Minolta SR-T 100X that sat in a thrift store window, came with a 45mm f/2 normal lens, pretty close to the perfect normal. It was an odd combination. The small lens did not balance well on the heavy metal body of the camera, and the aperture and focusing rings were too small. Yet something struck me: the lens always seemed to be the right one. It was almost never too tight, and almost never too wide. It felt right. It still does. On film, this has become my go-to lens for personal photography. I always come back to it when I want to travel light, but even when I'm close to home and have many lenses and cameras to choose from, I use it frequently.
For full frame shooters, perfect normal lenses are not easy to come by. Pentax used to make a 43mm lens, attempting to get as close as possible to the perfect normal focal length for 35mm film. Nikon once sold a 45mm AI-P lens, not autofocus but still compatible with modern cameras. Unfortunately, it has long been discontinued. Today, the company still makes a 45mm f/2.8 macro tilt-shift lens, but this is highly impractical and overpriced to use as a small normal lens. Apart from that, you have several choices of 50mm lenses (most prominently the f/1.8 and f1.4 G series lenses), but the next wider lens is a 35mm one. Canon makes a 40mm pancake and 50mm normal lenses (f/1.8 and f/1.4), but nothing in between.
APS-C photographers have it easier. There are 28mm lenses to choose from at many price points from a number of manufacturers, from the lowly SLR Magic toy lens for Sony's E-Mount, to the Leica Summilux-M and the Zeiss Otus. There are also several solid options at 30mm, such as Sigma's 30mm f/2.8 E-mount lens, its f/1.4 Art Lens, made in Sony A, Canon, Pentax, and Nikon mounts, as well as Sigma's own mount, or Sony's A-mount macro lens.
Fix Your Zoom
While I like my almost perfect normal lens, you don't need to go for exactly that focal length. You just need something in that range, maybe a bit wider or a bit tighter according to personal preference. You don't need an expensive lens. An old, used one will do. But what if you don't have a prime lens and you don't want to spend your hard-earned money on one, even a cheap one? Here's my modest proposal: use a sliver or two of gaffer tape to temporarily fix your zoom lens to one focal length, something in the normal range. (My preference, of course, would be the "perfect normal" focal length). I have recently done this with an old Nikon 28–105 zoom. Two small pieces of tape now hold it at approximately 43mm.
Make up a personal photo project for which you use only this focal length. Force yourself to see your surroundings as one lens sees them. Do this often, and you will soon get a feeling for images that float around you, almost as if frame lines appeared in the world, projected there by some Matrix-like magic. You will get a feel for your focal length. Go out on another day with your lens fixed to another focal length, and compare how you like using this one, but also assess which one seems to produce better images in your hands. In the end, that is what it's all about, and sometimes a tiny little hack can go a long way.