The information here is based on Nikon (Nikkor) lenses, but is generally applicable to other brands as well, especially Canon. (Canon and Nikon track each other's lens developments quite closely, with many lenses having identical specifications, down to the exact focal length and aperture.)
Emphasis is on indoors, available-light (no flash) usage. If photographing with flash or outdoors, the choice of lens is less critical.
For the standard DX focal lengths (18mm to 105mm or 135mm), there are three main types of lenses:
- f3.5-5.6 kit zoom lenses
- f2.8 professional zoom lenses
- f1.4 to f2.8 prime lenses
Kit lenses for Nikon are the 18-55mm f3.5-5.6 (D3000, D3100, D5000, D5100) and 18-105mm (D90, D7000). While cheap, kit lenses are capable of producing high quality photos. Image quality is usually rated as good by reviewers.
- VR image stabilization reduces camera-shake, allows hand-holding down to 1/8 or 1/15 seconds at 18mm.
- Small f3.5-5.6 aperture has large depth of field. Photographer doesn't have to be careful about focus accuracy or depth of field.
- Small and light.
- Cheap. This doesn't just mean affordable, it also means that it's less of a concern if it is lost, broken or stolen.
- Large depth of field makes it hard to throw background out of focus, for portrait photos.
- Small aperture makes it difficult to shoot at high shutter speeds in low light. Shutter speeds of 1/30 to 1/125 seconds are needed to reliably take clear photos of people, to freeze their movement.
- Plastic mounting ring is not as strong as the metal mounts found on more expensive lenses. They break more easily if the lens is knocked.
- Travel, every-day-carry.
- Handheld night photography.
- Indoor photos of people in dim light, unless flash is used.
Professional f2.8 Zooms
For professional photographers using 1.5x crop DX cameras, the standard lens is the 17-55mm f2.8 zoom. (Professionals using 1x crop FX cameras like the D3 and D700, usually use the 24-70mm f2.8 zoom.) For more reach, there's the 70-200mm f2.8.
- Larger aperture compared to the kit lenses. Double the brightness at 18mm, 4x the brightness at 55mm.
- Tough, solid construction, including metal mounting ring.
- No VR for the 17-55mm. The 70-200mm f2.8 is a VR lens.
- Big, heavy, expensive.
- General photography.
- Travel, every-day-carry.
Prime lenses are non-zooms. Except for a narrow focal length range (about 28mm to 85mm), they are significantly bigger, heavier and more expensive than the kit lenses. They can be cheaper and lighter than the f2.8 professional zooms.
- Large aperture. An f1.4 lens is 4x brighter than an f2.8 zoom, an f2 lens is 2x brighter than an f2.8 zoom.
- Tougher than zooms. There's no fragile telescoping lens barrel. The newer lenses are usually IF (internal focusing). This means that there are no moving parts outside the lens barrel aside from the focusing ring, only a single-piece plastic barrel, making the lens more resistant to knocks. It's not just the matter of the cost of replacing a banged-up lens. If you're on vacation somewhere, or trekking in the middle of nowhere, you might not be able to get a replacement.
- Usually but not always, big, heavy and expensive.
- No zoom.
- Portrait photos. The large aperture is used to blur out the background.
- Available-light photography: people and night scenery.
- General photography.
- Single-camera systems. You need two camera bodies otherwise you'll be swapping lenses all the time. Unless you use an intermediate focal length like 24mm or 35mm.
Game-changer: Today's High-ISO DSLRs
Looking at ISO speed:
- ISO 400 was about the highest acceptable for 35mm film. Film with higher ISO speeds were grainy (noisy).
- ISO 1600 was about the highest acceptable for DSLRs of only a few years ago (D300, D80). That's a 2-stop (4x) advantage over ISO 400. Setting the ISO above 1600 created noticeable levels of noise.
- ISO 6400 is about the highest acceptable for current DSLRs (D7000, D5100), looking like an older DSLR at ISO 1600. That's a 2-stop (4x) advantage over ISO 1600, a 4-stop (16x) advantage over ISO 400.
- Has the same or better low-light performance compared to a 35mm film camera with a f1.4 prime lens.
- Has the same or better low-light performance compared to an older DSLR with a 17-55mm f2.8 professional zoom lens.
Lens and Camera Combinations
It's not an "either/or" matter when it comes to choosing which type of lens to use. You could have a combination of kit lens, f2.8 zoom, and prime lenses.
A lens isn't used in isolation. When choosing a lens, you need to look at what other lenses it will be used with. It's also good to consider lenses with overlapping capabilities, so that if one lens fails, you can still finish the job without too much trouble. A kit lens or a 35mm f1.8, is a good backup lens.
Below are some suggested combinations. The factors also change if you have two camera bodies instead of one. Two cameras means you have a backup in case one fails. Since you have a backup camera, make the best use of it by putting a second lens on it and using it as a secondary camera.
Suggested lens combinations for one-camera systems:
- Kit lens for general photography, 35mm f1.8 as backup and for photographing people in dim light.
- 17-55mm f2.8 for general photography, kit lens or 35mm f1.8 as backup.
- 50mm or 85mm prime on first body, 12-24mm f4 wide-angle on second body, kit lens or 35mm f1.8 as backup. This combination allows you to cover a wider focal length range than the 17-55mm f2.8, while giving you more light at the telephoto end.
- 50mm or 85mm prime on first body, kit lens on second body, 35mm f1.8 as backup. Good balance of cost, weight and capability. Good for bright and small rooms.
- 85mm prime on first body, 35mm f1.8 on second body, kit lens as backup. Same combination of lenses as the above, only the kit lens and 35mm f1.8 swap places. Good for dark and large rooms.
- 85mm prime on first body, 17-55mm f2.8 on second body, kit lens or 35mm f1.8 as backup. This is a heavy and expensive combination, but it's a safe choice, using professional lenses on both bodies, with cheaper consumer lenses as backup.
You can get good results with a kit lens and flash (bounced or diffused external flash is best). It's only if you want to take available-light photos indoors, that you need to consider getting an f2.8 zoom or a prime lens.
If you have a new DSLR, boost ISO to 6400 when shooting indoors with a kit lens. See if you like the results. There's probably no need to get another lens, except perhaps the 35mm f1.8 as a backup or as a cheap way to test the prime lens waters.
If you have an older DSLR, it makes more sense to get a new DSLR, than to get a new lens.