The question of what camera lens to use in a given setting and scene or on a particular subject is as old as the DLSR shooter itself. And this is mostly because one’s lens or focal length choice is pegged on a variety of factors including experience, instinct, camera type among a host of other subjective elements.
While some people size up their desired focal lengths based on the range of the subject, other photographers rely on the clarity, lighting, and prevailing weather conditions to determine the minimum full-frame focal length to use. But as you may already know, the focal length refers to the distance from the lens’ optical centre to the digital camera centre when the image is in focus. It is usually measured in millimetres and displayed in the viewfinder as soon as the object comes into focus.
Now, speaking of the viewfinder, there are two main types of lenses as far as the focal length is concerned- the prime and the zoom. Prime lenses come with fixed focal lengths while zoom lenses are typically adjustable. And as for prime lenses, you can expect to find variations such as wide-angle (15 to 28mm), standard (35 to 80 mm), telephoto (80-300mm) and the super telephoto lenses (200-400mm).On the other hand, under the zoom category, there are varieties such as standard to telephoto and the wide-angle to telephoto coverage.
So one may ask, how does the type of lens influence the nature of the image taken?
Well, for starters, contrary to what most people think, it’s the type of object to be photographed that influences the type of lens used, which in turn determines the focal length in question. Everyday objects such as flowers, pets, interior décor, etc., for instance, are best captured using standard lenses. These lenses can accurately replicate the human eye’s optical ability resulting in more realistic images.
Wide-angle lenses, on the other side of the spectrum, are best suited for photographing groups of people, landscapes or even taking selfie photos. Telephotos are used for zooming or enlargening distance objects while super telephoto are mainly used for capturing images of wildlife and birds.
Notably, the above conclusions are drawn from the fact that the appropriate focal length in any setting is given by the Image Size multiplied by the Distance and the result divided by the Object Size. (from elementary science class). Nonetheless, since it is impossible to measure or estimate the exact image and distance size using the naked eye, groups of lenses with different focal lengths were invented to counter this. That’s why you’ll notice that a wide-angle lens has a broader field of view than a standard lens though the latter has a greater focal length.
The bottom line
If you have just started photography recently and haven’t yet mastered the dynamics of calculating image and distance sizes visually, then you will be safer sticking to the above guide or risk blurring out and over-exposing your shots.