Free Sample
The Complete Handbook of Lens Converters
A practical reference for photographers, filmmakers, and optical engineers on selecting, using, and maintaining teleconverters, wide-angle adapters, and macro couplers.
by Alumigogo Books
Chapter 1: Understanding Lens Converters
A lens converter is an optical unit that mounts between the camera body and the lens to change the effective focal length of that lens. It is a simple concept with profound consequences. A 1.4x teleconverter placed behind a 200mm f/4 prime lens turns it into a 280mm f/5.6 optic. A 2x teleconverter makes that same lens a 400mm f/8. The physical length and weight of the combination remain essentially those of the original lens, but the practical reach has changed. For a working photographer who cannot afford an 800mm super-telephoto, the converter is a bridge to that reach. For a cinematographer shooting a documentary, a wide-angle adapter can transform a standard 24-70mm zoom into a 17mm ultrawide for a confined interior. This chapter explains the mechanics of these changes, what actually happens to the light as it passes through the added glass, and why a converter is never optically free.
To understand a converter, you have to stop thinking of it as an accessory. It is an optical system in its own right. When you mount a 1.4x converter, you are placing a set of lenses between the rear element of your main lens and the image sensor or film plane. These added elements intercept the cone of light that the main lens is projecting and expand it before it reaches the sensor. The expansion of the image circle is precisely what produces the effective increase in focal length. The image that lands on