still ask if they can use old 35mm-film lenses on new DSLRs. The answer is yes you can, but you probably won’t want to. Why? Because digital sensors handle light differently than film. Designed-for-digital lenses focus light differently to better register on the image sensor, and digital-specific coatings maximize color and sharpness. Plus, newer lenses often are sharper than old ones—and that’s increasingly important with high-res sensors.
Choosing the perfect lens means more than just buying the newest models, though. Fit a lens to your personal style and the things you photograph most often, as well as the features and budget that meet your needs. You don’t have to buy the most expensive glass to make the best lens choice. You just have to understand which features will provide what you’re looking for.
The focal length of a lens is the first thing most photographers look at when considering a lens. It’s the most apt broad definition of what a lens does—and that’s providing a field of view that’s normal, wide or telephoto. Normal lenses approximate the human eye, somewhere in the 40-60mm range. Wide-angles are shorter than 40mm (and most often somewhere in the 20s), while telephotos are 70mm or longer.
Wide-angle lenses are great for cramped spaces or to make landscapes look even more vast. Short telephotos (in the 80-150mm area) are great portrait lenses, while longer glass (200mm, 300mm, 600mm, even 800mm) is ideal for getting close-ups of small and distant subjects, like sports and wildlife. Telephotos compress a scene greatly in the opposite way that wide-angles expand a view.
All of these measurements are given in 35mm-film-equivalent terms. When working with sensors smaller than full frame, focal lengths will behave proportionally longer. Some lenses are designed exclusively for small APS or Four Thirds formats and will work only with those particular cameras. To make comparing lenses easier, though, manufacturers often refer to focal lengths in standard 35mm-equivalent terms.
If a lens is a fixed focal length—35mm, 50mm or 100mm, for instance—it’s known as a prime lens. If a lens covers a range of focal lengths, like 28-70mm, it’s a zoom. Choosing primes or zooms is largely a matter of personal preference. Would you like one lens that covers the range of three primes in order to travel light or work quickly? If you want one lens to do it all, an extreme zoom that covers everything from wide-angle to telephoto could be perfect. Or if you want a handful of lenses that are fast and do one thing really well, consider purchasing primes.