Understanding the Focal Length of Telephoto Lenses in Photography
The focal length of a telephoto lens is a critical component in the world of photography, especially when it comes to capturing distant subjects in detail. These lenses are meticulously designed to magnify distant objects, allowing photographers to isolate their subjects from the background without physically getting closer. However, defining the exact range of focal lengths that constitutes a telephoto lens can be a bit nuanced depending on the sensor or film size. This article will explore these concepts in detail.
Defining Telephoto Lenses
A telephoto lens typically has a focal length ranging from around 70mm to 300mm or more. These lenses are designed to compress the perceived distance and magnify distant subjects, which is incredibly useful in various photographic niches like wildlife, sports, and portrait photography.
Telephoto Range and Crop Factors
One common confusion arises with crop factor lenses. For instance, a 100mm lens on an Olympus camera with a crop factor of x2 will effectively become a 200mm lens, thus extending its telephoto range. This is because the crop factor essentially multiplies the focal length, altering the perceived magnification. Similarly, a lens of 70mm on a full-frame camera might seem relatively wide, but on a crop sensor, the same lens can act like a 70mm telephoto lens.
Lens Zoom and Typical Ranges
These days, photographers often use zoom lenses for telephoto photography. For a full-frame camera, the typical zoom range for a telephoto lens is 70-200mm, with some cheaper lenses stretching to 70-300mm. APS-C cameras usually have a 55-200mm or 55-250mm range. When longer lenses are required, such as for bird, animal, or sports photography, lens lengths like 300mm or 400mm might be used. These longer lenses can be bulky and heavy, hence the preference for mirror lenses or other alternatives.
Absolute Telephoto Focal Lengths
The focal length that is considered telephoto can vary significantly based on the size of the film or sensor. For example, a 50mm lens on a 35mm film frame is considered “normal,” while an 80mm lens on a 35mm frame is considered “telephoto.” However, on an 8x10 frame, a 300mm lens would be considered “normal,” but on a 35mm or smaller sensor, it would be classified as telephoto.
Critical Thresholds
The distinction between a wide angle, normal, and telephoto lens is often based on these critical thresholds. For full-frame digital or 35mm cameras, a 45mm-55mm lens is typically considered “normal,” and anything 60mm and longer is considered telephoto. Conversely, on digital 4/3 systems, a 25mm lens is considered normal, and anything under 20mm is wide-angle, while 30mm and up is telephoto. These distinctions are quite relevant for understanding how different focal lengths interact with various sensor sizes in photography.
Conclusion
Telephoto lenses are incredibly versatile and are used in a wide range of photography situations. Understanding the focal lengths and how they interact with different sensor sizes is key to mastering telephoto photography. From the classic 135mm to the ultra-long 1200mm, telephoto lenses offer photographers a variety of tools to capture the most detailed and nuanced imagery.