Photographers dream of telephoto lenses. They allow you to get close to faraway subjects with little effort and offer a good chance at capturing detail. No wonder powerful zooms are always a strong selling point for camera buffs. They can be a great tool providing you learn to use them properly.
The first consideration is stability. When you look through powerful binoculars or a telescope, the first thing you notice is how jittery the image is. That’s because every small movement of your hands or fingers is amplified. Time for a tripod or, at the least, a monopod. In a pinch, setting the camera on a table will work - provided it’s a steady table.
This is a necessary inconvenience. The fact that the telephoto lens has such great magnification is, in spite of the challenges, a great asset. By getting in close on distant subjects, you can capture details that often go unnoticed.
Long telephotos are great for photographing wildlife. By staying further away you avoid scaring birds and other small critters, plus the longer lens allows you to keep a safe distance from potentially more dangerous wildlife.
Medium telephoto length is very useful for portraits taken without your subjects noticing you. You’ll get better, more casual snapshots of people who are intimidated by cameras, and you’ll avoid people who tend to overpose.
Telephoto lenses also do a great job of “flattening” perspective. Objects suddenly seem very close to each other, even cluttered at times. A sparse gathering can sometimes look like a crowd, a few tree trunks like a dense forest, or a thinly populated flower bed like a colorful, lush, saturated block of solid color.
Telephotos also have relatively thin depth of field, making it easier to isolate a subject by leaving both the foreground and background out of focus. This is great for capturing a detail, or for portraiture.
Luminosity is important for a telephoto lens. Especially if you want to take action shots or sports. Not only does a more luminous lens afford you the higher shutter speeds you need for stopping action, but it will also help with indoor sporting events. You’ll still need to use high ISO values, because you’ll also like the extra depth of field you get by stopping down slightly.
Of course luminosity comes at a price, especially in the longer telephoto range. Expect to pay quite a bit more for those extra two stops you want.
Stabilized lenses are great. Even with long focal lengths, stabilization will often allow you a couple of stops or more latitude.
Still, you need to be careful. With image sensors capturing more and more fine detail, you need to maintain high speeds to keep all those tiny pixels sharp!
The rule of thumb in the films days was to use a shutter speed number at least as high as the lens focal length. For example, 1/250th of a second for a 200mm lens.
Stabilized lenses allow for reasonable images at lesser speeds. But if you want your images tack sharp, you should still use the highest speed you can manage.