In the first three parts of the lens purchasing guide I focused on standard zoom lenses, which tend to be the most popular among consumers and pros alike. There are other options though, especially if you need "faster" lenses, but don't have money for pro quality lenses such as the Nikon Canon 24-70mm F2.8 lenses. As the title of this section indicates I'll be discussing prime lenses, and why you should consider using them.
Why should I consider "Prime" lenses?
Prime lenses tend to have a few advantages over zoom lenses, although not all of these advantages are true in ever case. Historically the most sold lens for any SLR system would be a 50mm F1.8 prime lens. Part of the reason behind that popularity was/is the low cost of these lenses. In the case of Nikon and Canon, their respective 50mm F1.8 lenses are the cheapest lenses in their lineups. The other reason that 50mm lenses give us a closer view of what we normally see with the human eye (peripheral vision aside).
Another advantage of some prime lenses is size and weight. There is a big difference between holding a 24mm F2.8 prime and using a 24-70mm F2.8, not to mention that storing primes in your bag is a lot easier. Then again you look at Nikon's new 24mm F1.4G and you start to notice that it isn't very light or small. That brings up the next point, prime lenses don't have to be small, light or cheap though, just look at the price of a 400mm+ telephoto lens, or the previously mentioned 24mm F1.4G Nikkor and you'll be hard pressed to find one that would fit those descriptions! On the other hand many of the old prime lenses from Nikon and Canon are low weight and can fit in your pocket. The great part of these smaller prime lenses being pocketable is that you can carry two or three of them (one on camera, two in jacket pockets), so that you can change to the focal length you need in short order.
Prime lenses make you think about your composition, because there is no zoom ring to grab to change what you see. The zoom ring for a prime lens is your legs! The good news is that prime lenses either perform as well as or much better than many zoom lenses, in most cases. In recent years lens manufactures have worked hard to get zoom lenses to match or exceed the quality of some prime lenses. For an example compare the quality of a Nikon or Canon wide angel prime (24mm or 28mm) and you'll notice that the companies 24-70mm lenses often out perform those primes.
What Prime Lenses Should I Consider?
That depends on what you like to photograph, so you need to make choices based on your needs, just as you would with a zoom lens.
A Normal Lens:
On a Crop Sensor Camera: On a crop sensor camera a 35mm-30mm (1.5x Nikon, Pentax, Sony), 30-28mm (1.6x Canon) or 25mm (2x 4/3s) prime will come close to the coverage given by a 50mm lens on a 35mm SLR, so if you are looking for a "normal" lens consider one of those lenses.
On a Full Frame (35mm Camera): On a full frame camera a 50mm lens will be normal so there is no need to look at different focal lengths to get the coverage. You just need to pick what aperture of 50mm lens that you desire or need. The most common versions are 50mm F1.8, F1.4 and then the expensive F1.2. Unless you shoot with nature light indoors a lot the need for an F1.2 lens is somewhat limited, although it is important to note that the wider the aperture the sooner the lens gets sharp at other wide apertures. In most cases 50mm F1.4 lenses are going to be sharper at F2 than the lens that start at F1.8.
Wide Angel Primes:
This is the area that becomes troublesome, because of the current crop of auto focus wide angel primes very few of them give image quality as modern zoom lenses. For example, the Nikon 14-24mm F2.8G, trumps all of the wide angel primes that Nikon has made in the last 50 years! Canon and Pentax's wide angel primes do have a bit more performance than Nikon's, but still fall behind the 14-24mm Nikkor, based on every test that I have seen. Of course the prime lenses win in terms of size and wight. The only lens that comes close to or could be better than the 14-24mm F2.8 Nikkor would be the Nikon 24mm F1.4G, which is faster, but also $400 Cdn more and not much lighter or smaller either!
Some of the older manual focus primes made by Nikon and Canon are good, although not as good as the mentioned Nikon zoom. The nice thing about the older manual focus primes is that they are generally very inexpensive, but can only be found in used condition. In the case of Canon users you would need to get an FD to EF adapter, since Canon switched lens mounts when they introduced auto focus cameras.
Common wide angel primes are 20mm, 24mm, 28mm and 35mm, but there are also wider angel lenses and fisheye lenses. These ultra wide angel lenses (14mm, 16mm, 18mm) tend to be very expensive, even used because they were not produced in large numbers. Fisheye lenses (some as wide as 10mm or even 8mm) were designed for underwater photography, to counter act the bending of light underwater, but many photographers have found use for these lenses above the water line. Through modern software like Gimp and Adobe Photoshop you can correct the fisheye effect to create ultra wide angel views for all encompassing landscape shots or architectural photography. The problem is that when you use the distortion correct you lose detail on the corrected areas, which can be problematic in the types of photography that people might want to use these lenses.
Telephoto Prime Lenses:
To start off, none of these lenses are cheap or light weight other than 85mm F1.8 lenses which are the smallest and lightest of the bunch. Once you step up to a 85mm F1.4 lens the size and weight increases and then you move onto 105mm and longer lenses, which are going to cost $1000 or more. When it comes to long telephoto lenses you will sometimes have a choice between fast F2.8 lenses (up to 400mm) and F4 or F5.6 versions. The smaller aperture lenses have the advantage of being smaller, lighter and less expensive, but a 400mm F4 lens is still going to cost around $4000-5000 Cdn dollars! Canon does offer a 400mm F5.6 lens that is price around $1400 so if you need a lot of reach and don't have a lot of cash that is an option. Of course another possibility is to get a 300mm F4 lens and use teleconverters to achieve the same or greater focal lengths, although the cost is about the same so if you shoot with Canon and do not need the IS of the 300mm F4L or don't want to lose image quality to a teleconverter then consider the longer lens. For a Nikon shooter looking for a 400mm F5.6 the 300mm F4 AF-S with a 1.4x TC is the only way to come close to that. With a 1.4x the 300mm lens becomes a 420mm lens, so it is a little bit longer in fact. If you have more money than you could use a 200mm F2.8 lens with a 2x TC to get a similar focal length with an aperture of F4.8. That doesn't seem like a big difference, but you gain half a stop of light, which depending on your subject could mean the difference between getting the shot or not!
Once you get to super telephoto lenses (500mm or longer) the prices get insane, with lenses such as the Nikon 600mm F4 VR costing around $9500 Cdn! If you can afford it you could attach a 1.4x TC and have a 840mm F5.6 VR lens! Use the combo on a crop sensor body and you'll have a 1260mm field of view! Of course a lens like that will have to be shot from a tripod as the lenses can weigh over 10 pounds, which could never be held steady enough by hand for a sharp image. Canon's longest lens is the 800mm F5.6L, which would give a similar field of view and likely better image quality since it does not require a teleconverter. Most photographers that I have seen who own these big lenses carry them in a rolling cart, because they cause fatigue after a short time of carrying them by hand.
If you shoot macro photos of bugs or other small creatures then you would want to look at a 105mm F2.8 or if possible a 200mm macro lens. Of course these lenses will set you back $800-2000, so you might not be able to start out with such lenses.
Prime lenses do have some advantages over some zoom lenses, but they might not be right for you. They can be a cheap alternative to getting a fast standard zoom, but once you get into the ultra wide angel or telephoto prime lenses the prices can get high or even extremely high! A 24mm F2.8 lens could be very small, light and discrete, but a 800mm F5.6 will stick out like a sore thumb and weigh a lot! As with any other camera gear, try the lens out if you can before you buy it. If you are not sure what to get there are lens rental services, which would give you a chance to try out a lens before you buy. Another advantage of lens rentals is that may be able to rent a lens that is out of reach for you financially.