Mounting Individual Lenses

• Published in: Mounting Optics in Optical Instruments p. 1
• Main Author: Yoder Paul R. Jr
• Format: Book Chapter
• Language: English
• Published: SPIE 2008; SPIE Press
• Edition: 2nd Edition
• Subjects: Geometric & Physical Optics; Optics & Photonics
• ISBN: 9780819471291; 0819471291
• DOI: 10.1117/3.785236.ch3

In this chapter, we consider several techniques for mounting individual lenses in optical instruments. These techniques are most applicable to optics with apertures in the range of approximately 0.25 to 16 in. (6 to 406 mm). Although most of the discussions deal with glass lenses interfaced with metal mountings, the same principles are generally applicable to lenses made of optical crystals and plastics. Numerous examples are included to illustrate the use of given design equations. Our first topic deals with estimation of the appropriate axial preload applied to the lens at assembly so that it is held firmly against the mechanical interfaces under all expected adverse environments, including combined extreme temperature and acceleration—the latter directed along any of three orthogonal axes. In order to define this preload, we need to know the weight of the optic. Therefore, standard equations and numerical examples are given for calculating this parameter. We also present equations for locating the lens's center of gravity. The discussion of lens mounting designs begins with inexpensive, lower-precision techniques. Designs with threaded retaining rings and with compliant ring flanges are considered next. Then we describe the common types of glass-to-metal interfaces: sharp corner, tangential, toroidal, spherical, and flat and step bevels. The chapter continues with descriptions of ways to mount lenses and nonsymmetrically shaped optics in elastomeric supports and on flexures. It concludes with brief considerations of mountings for plastic lenses. The all-important subject of aligning the lens in its mount is considered in Chapt. 12. The total axial force (preload), , in pounds, which should be exerted on the lens by any means of constraint to hold it in place against its mechanical reference surface, may be calculated as the product of lens weight and the worst case axial acceleration. Theoretically, the latter term is the vector sum of the axial components of all the maximum anticipated externally applied accelerations, such as those due to constant acceleration, random vibration (3σ), amplified resonant vibration (sinusoidal), acoustic loading, and shock. For simplicity, frequency effects are ignored, the accelerations are expressed as a multiple of ambient gravity, and friction and moments imposed at the interfaces are neglected. Because all types of external accelerations do not generally occur simultaneously, the summation does not need to be taken literally. If is a single-valued, worst-case number, then If the lens weight is expressed in kilograms, Eq. (3.1) must include a multiplicative factor of 9.807 to convert units. The preload is then in newtons (N). The subscript “ ” indicates that this preload is associated with the axial motion of the optic.