Early telephoto lenses such as these produced by H. Dallmeyer were expensive and specialised until the popularisation of SLR cameras in the 1960s enabled much more widespread usage.
38 : Telephoto lens
1891
Early telephoto lenses such as these produced by H. Dallmeyer were expensive and specialised until the popularisation of SLR cameras in the 1960s enabled much more widespread usage.
The rapid expansion of photography in the 20th century meant that specimen hunting and the field skills learnt for the stalking of game and trophies could gradually be adapted to the less harmful observation of birds and the shooting of images. The post-war acquisitive hobbies of listing and twitching could also be said to have partly replaced trophy hunting.
But even birders with the best field skills are still only able to get face-to-face with their quarry very rarely, and it was the evolution of magnifying lenses that enabled feather-by-feather details to be captured forever by photographers.
The principles of the telephoto lens were initially theorised in Johannes Kepler’s Dioptrice (1611), but became more fully realised in 1834 when military mathematician Peter Barlow created a prototype. Perhaps the first true and practical model was developed by Thomas Dallmeyer in 1891, though a few other engineers made similar lenses almost simultaneously. Their use remained specialised until the 1960s, when the popularisation of single lens reflex (SLR) cameras brought them within the reach and ability of press and sports photographers, as well as bird photographers.
The lenses needed to photograph birds up close can be divided into three broad types: telephoto, in which the length of the actual lens is shorter than the focal length (the distance over which light rays converge into a focus point within the lens tube); zoom, in which the focal length is varied to allow close-up or more distant shots; and long-focus, which has but one internal lens element and needs a long body to allow the light rays to coalesce on the focal point (these remaining at a single length and therefore a single magnification). This last lens type has become less frequently used by hobbyist birders in favour of the flexibility that can be gained from telephoto and, especially, zoom lenses.
The overall effect of both is magnification of the image, like having a telescope attached to a camera, a set-up now literally possible with digiscoping (see pages 190–191). A telephoto lens is constructed from more than one lens, unlike a fixed focal length camera lens, allowing truncation of the focal length within a shorter lens body by changing the angle of the light rays’ paths onto smaller lenses.
The focal length of a zoom lens can be varied either parfocally, by sustaining focus as the lens zooms in and out, or varifocally, meaning refocusing is needed as the focal length changes. Zooms were first developed in telescopes, being described in 1834, but the first use in a camera was documented in 1902 by the US Patents Office, registered to Clile Allen. First manufactured in 40-120 mm format in 1932 for cinema film cameras, zoom lenses only came into mass production for still cameras in 1959, and again were popularised during the 1960s for the more affordable SLRs.
The elusiveness and/or distance of birds in the field has meant that such lenses have become a real boon, and it is now common to see birders as well as photographers carrying them alongside a multitude of other gadgetry. The days when birders would throw ‘bins’ and book in a bag and go birding are long gone, it seems, as indeed are the days when a sketch and a description would confirm a difficult identification or record – now only a photo will do.