For a few years now, Iīve had in my collection one very strange lens. I bought it primarily for itīs value as a collectible so, up until now, I havenīt really spent much time playing with it.
Made in 1975, this manual focus Minolta MC Rokkor-X 40-80mm F2.8 lens is one strange puppy. When it was first introduced, no other zoom lens could top its image quality and it really didnīt have much competition until more recent years. This is largely due to its very unique Gearbox design that sought to overcome the problem with zoom lenses that we still face today.
Way back in 1959, the first commercially-available 35mm still camera zoom lens, the Bessematic-mount Zoomar 36-82mm F2.8, was released by Voightlander. Itīs mechanical design would not be unfamiliar to you since the focus and focal length were adjusted via a few round-turns of the lens barrel.
This simple helicoid design remains the only common method manufacturers use to make our lenses zoom in and out and focus. When you twist the zoom/focus ring(s) of a lens, the optics are carried forward or backward through a threaded barrel. This design results in a fixed movement ratio of the optical groups mounted inside that helicoid. The problem with this is every focal length requires a slightly different adjustment of the lens element/group spacing to properly correct aberrations and the fixed ratio of a helicoid cannot provide that kind of variance.
The helicoid is relatively simple, easy to make, and its shape tailors to a fitting physical design of a lens. If a lens were designed to have as few compromises as possible, it might look vastly different from what we see sitting on store shelves. For simplicity though, manufacturers have stuck with the helicoid and instead invested in overcoming its mechanical shortfalls with optical solutions.
Over the years, lens designers, aided by computers, have learned how to improve the optical designs of the zoom lens to work around most of the limitations o ...
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