After more than a century from the introduction of zoom lenses, the selection of the right zoom lens type for a
given specification is still a challenge for the optical designer In the process of lens design, the optical designer is
permanently searching for the best zoom lens structure in order to fulfill the complex balance between weight,
cost and optical performance This is a continuous optimization process and the result is a global optimum The
most important factors influencing zoom lens cost are: the number of spherical and aspherical lenses, the number
of moving groups and lenses and finally the group sensitivity to displacement and tilt Every lens group whether
moving or not inside the zoom lens, has a specific complexity and sensitivity behavior dependent on the zoom
lens type It is not obvious which type of zoom lens will optimally satisfy the required specification This paper
describes the selection process exemplary for a zoom lens with a medium focal length range from 28mm to 80mm
and a quasi constant f-number (FNO) during zooming The lens is used mainly for cinematographic applications
and must be able to maintain best image position for the entire range of object positions during zooming
Alternative solutions with their advantages and disadvantages are shown, analyzed and evaluated

Toward the global optimum in zoom lens design

Relaxation of various restrictions has led to new zoom lens types which include multiple zooming groups and advanced concepts for focusing. New designs can now rival fixed focal length lenses for most applications, and with the use of aspherics can be low cost. Gaussian optics and primary aberrations are used to obtain good starting design types.

Zoom lens principles and types

Reflective optical surfaces offer lower aberrations than the equivalent refractive optical components and they are also free of chromatic aberrations; so the use of reflective surfaces in zoom systems should lead to better performance than the equivalent refractive systems This is clearly a naive view because it ignores the problem of central obstruction and also the very low level of complexity of a reflective zooming group (at least notionally a single surface) On this bases we have exploited the additional complexity that Mangin or back-reflective mirrors offer, showing how a high degree of correction over a modest zoom range may be achieved with remarkably compact constructions

Application of catadioptric mirrors in zoom optical systems

The modern zoom lens for 35 millimeter photography has a focal length range extending from the wide angle to telephoto, potentially replacing several single focal length lenses or zoom lenses of small range as the standard photographic objective. This recent development appears to be the result of a continuous design evolution; each new design widening the range of power change utilized by the particular configuration. When a particular configuration is extended too far, the lens design necessary for aberration correction becomes complex, and a new configuration is developed.

Ellis Betensky

Papers

The Modern Zoom Lens For 35 Millimeter Photography