Tolerancing plans range in complexity from those in which all parameters are investigated, documented, and controlled to those that rely solely on whatever quality of optics, mechanical parts, and assemblies is present. The level of complexity desired depends not only on technical considerations but also on cost, schedule, etc. An outline is presented which is applicable not only to the more complex tolerancing plans but also to more modest efforts. The various activities and documents of the complete tolerancing plan are described and illustrated with a view toward clarifying their functions. The outline together with the activities and documents should provide a point of departure for establishing an effective tolerancing plan in a given situation.
This paper describes a Computer Image Simulation System (CISS) developed by EIKONIX. The system produces imagery from simulated visible and infra-red optical systems using either film or solid-state detectors. The CISS has been used to formulate and evaluate specifications for several remote sensing systems. Our experience has shown that computer modeling can be an important tool for producing an effective and efficient system design. The EIKONIX CISS consists of six basic components each of which simulates an aspect of the imaging process: scene generation facility; atmospheric model; collection system model detector model; data channel model; and soft and hardcopy display facility. Together these components provide "end-to-end" simulation of an optical system and its product. The purpose of this paper is to describe the components of our system and to illustrate its use.
The cost of Far Infrared Optics used in Night Vision Thermal Imaging Systems is an appreciable percentage of the total system cost. Testing and specification of these optical components can either increase or decrease the final cost of the system. The choice of test equipment and procedures as well as specification of unassembled elements are large factors in the cost of finished optical components. Through an understanding of the appropriate specification and a judicious choice of testing, quality Far Infrared Optics can be fabricated at reasonable cost.
The objectives of the engineers and procurement organizations are identical: "Get me the best part for the best price and on the best schedule." Implicit in this statement is the need for early com-munication among the engineer, procurement organization and the manufacturer. Inevitably, the discussions will center on specifications of components, subassemblies or total systems. The specification of optical components is frequently difficult to relate directly to the total system performance. Significant difficulties also arise with component specifications which may be subjective, and cannot be easily quantized for their effect on the performance of the system. In addition, the subjective specification for optical components or subsystems may have the greatest impact on cost and schedule, as well as being a determining factor for being able to successfully enter into high-rate production fabrication. It is not intended that the engineer should compromise system performance for simplicity of fabrication. However, it must be understood that the "best part" may not be necessary to achieve the desired goal.
Specifications establish tolerances which influence yield of component parts manufacture and tolerances applied to components affect the yield of final assemblies to specific specifications. A simple illustration is presented to demonstrate a technique for evaluating the relationship between specification and component tolerances.
A 1024 x 1024 pixel image digitizer has been developed that provides high speed electro-optical scanning of image transparencies. The system consists of a linear diode array mounted on a stepping motor assembly to produce a 1024 x 1024 pixel array. An optical system projects image transparencies onto the detector at variable scales. One design utilizes a 5:1 zoom lens with 1.0x and 2.4x channels for selection of image sample spacing from 1.3 to 16µm. Another optical design utilizes projection optics to enable sample spacing above 16µm.
Virtually all optical systems have some possible interpretation as a visual optical system. Often though, a detector such as a vidicon or photographic film intercedes to record the image. In such cases several quantitative methods have been devised to specify the required aberration content and fabrication tolerances for the optics used in such systems. Direct visual systems are the oldest of optical systems, but generally lack a good quantitative basis for tolerance specification. This condition has been accepted because the human eye is a remarkably adaptive organ, which will accept imagery that appears to be unacceptable by many of the accepted quantitative measures. On the other hand, the eye is bothered by such defects as scratches, digs and other cosmetic errors that are not consequential to many other optical systems.
This paper presents a cursory discussion of the visual optical system, its principal characteristics and the means by which they may be specified. A typical visual system will be discussed in detail, illustrating the required breakdown of its specification into two major areas, basic optical characteristics and system image quality. Consideration of the test procedures that will be precipitated by an unduly comprehensive specification leads to a discussion of those characteristics requiring actual testing vs. those that may be adequately proven by design calculations and documentation.
In choosing the proper technique for testing the optical figure of a high-performance aspheric mirror, it is appropriate to prepare a complete error budget for the test and to analyze the individual elements thereof to ensure that the measurement uncertainty is within acceptable limits. Such an error budget has been defined for the Hindle Shell test of a convex hyperboloidal secondary mirror for a hypothetical high-performance Cassegrain telescope system. A residual figure error of λ/80 rms at λ = 0.6328 μm is assigned to this mirror. This paper establishes the rationale for the error budget and develops specifications for the test system and equipment components. The importance of measuring and subtracting the error contributions of the test set-up and of data processing to remove certain systematic errors is pointed out.
The University of Dayton Research Institute has developed a system for the automated reduction of straight-line and circular fringe patterns. The system was designed for the Air Force Weapons Laboratory at Kirtland Air Force Base and is composed of three major hardware components: an automated pattern processor (ZAPP); a computer-controlled television-based digitizer (EyeCom); and a PDP-11/34 minicomputer. The ZAPP scans straight-line fringe patterns, displays the fringe center coordinates, and computes the peak-to-valley and RMS wavefront. The computer processes the fringe coordinates for wavefront analysis. When fully operational, the EyeCom will digitize circular fringe patterns, and then the fringe-acquisition program will manipulate the data to provide appropriate inputs for wavefront analysis. Outputs of the computer analysis are wavefront deviation, Seidel aberrations, Zernike coefficients, diffraction intensity spread function, Strehl ratio, optical transfer function, and geometric spot diagrams.
The designer of a reflective system must make some fundamental decisions regarding performance, environment, weight, component interfaces and cost, which ultimately affect procurement and manufacturing specifications. From the conception of system philosophy, scope and performance criteria, each component must be analyzed for function, integrity and manufacturability, and each phase of processing defined, in order to insure design requirements.
The surfaces of diamond machined optics are described in terms of the spatial frequency of the errors. Certain of these errors which are unique to diamond machined optics, such as, the highly correlated errors due to tool advance and the error due to machine centering uncertainty, are discussed in detail. The imaging effects of the errors are derived. A framework for specifying diamond machined optics, based on the imaging effects is presented.
Two additions to the popular "Metal Mirror Selection Guide" are proposed. To aid in specifying metal mirrors, some common terms and uses must be resolved. Mirror surface finish, contour, and outline shape, as well as aspect ratio, all affect both prices and quality. Part one definitizes these issues. Proper mounts for metal optics present a seemingly impossible design problem. Common design faults and their affects on optics present severe obstacles to proper system function. A well proven approach - called dual interfacing, has proven to be unusually effective in correcting these problems. Part two of this paper discusses and illustrates the problem as well as the working solution.
With the development of new, high precision optics production machinery there is a need to re-examine tolerancing of cosmetic standards, physical dimensions and optical performance. This paper will deal with some of the tolerancing trade-offs developed at Plummer Precision Optics, which have proven successful in reducing manufacturing costs without adversely affecting optical performance.
Plastic optics have come a long way since the first lens was injection molded many years ago; in fact today, the replacement of conventional optical components seems to be one of the least exciting aspects of polymer optics. Like waveguide optics, holographic optics, and coherent optics, plastic optics offers freedoms and options simply not available in conventional glass optics. This is not to say that plastic is not well suited to substituting for glass in many ordinary applications. The real virtues of plastic become clear, however, when one takes advantage of the medium to produce a totally unconventional component. Fig. 1 depicts a precision polygon having internal facets - a part whose manufacture is not possible using conventional glassworking techniques.
The effects of cosmetic defects such as scratches and digs as well as surface cleanliness are seen as increased veiling glare. Veiling glare lowers the contrast transfer function of camera objectives. Simplifying assumptions allow this effect to be estimated. Experimental data indicate that surface quality standards required for cosmetic reasons are higher than might be imposed for the purpose of maintaining image quality.
The measurement of the scattering characteristics of coatings and surfaces has not kept pace with the development of the software tools used to analyze stray light in an optical system. The use and importance of such measurements is emphasized by the use of a parametric analysis performed on the Spacelab Two telescope. The basic measurement of the BRDF need not be costly nor time consuming, but it is made clear that the data should be extensive enough to properly define the scattering function, not just a single profile of the function. The current forms of presentation used to define the stray light performance of optical systems are discussed. In most cases it is one of these definitions that is used to set the specification on the performance of a sensor. The definitions are all based on the point source transmittance of the system. When a broad source transmittance is used to define a specification many factors external to the system are involved and these mask the propagation characteristics of the sensor, and therefore make improvements more difficult.
At the present time there is no specification that is generally accepted by the optical community which can be used to specify optical scatter. In this paper the general content of such a specification is proposed. A first step is the choice of a suitable calibration standard for scatter. It is proposed that a calibrated set of SiC mirrors be used for this purpose because these mirrors are hard, durable and can be fabricated with a surface microirregularity down to 10Å rms. Two methods are proposed for measuring optical scatter: 1) Total Integrated Scatter (TIS); and 2) Bidirectional Reflection-Distribution Function (BRDF). It is important to consider both methods. TIS is simple to measure and can be used to calculate surface microirregularity. On the other hand BRDF gives scatter a function of evident angle. The major points of the proposed scatter specification are outlined, taking into account that scatter can be defined either by TIS or BRDF.
Standards for optical surface quality are suggested to address two distinct problems: (1) the cosmetic appearance of the optical component and (2) its functional performance in an optical system. For the first problem, a series of standard scratches with appropriately defined profiles is suggested, so that the visual appearance of the standard scratch matches the appearance of scratches produced by normal optical polishing. For the second problem, we suggest a measurement of total integrated scattering, which can be related quantitatively to the rms height of surface microirregularities. The scattering from scratches of differ-ent sizes can also be made quantitative. Angular scattering is too dependent on surface properties to permit it to be a useful standard. However, total integrated scattering is useful for approximately predicting the relative amounts of light scattered at a given angle by surfaces having different roughnesses.
This paper is a report on a conference, Standards for Scattering from Optical Surfaces, that was held February 6 and 7, 1979, at the National Bureau of Standards in Boulder, Colorado. Approximately 50 scientists attended and heard a dozen invited papers and a panel discussion. The visitors agreed, among other things, that national physical standards are needed. There was also general agreement that NBS should consider providing measurement services (such as well characterized surfaces) based on a state-of-the-art facility for precision scattering measurements and calibrations.
The requirements for high performance thermal imaging electro-optical systems have stimulated the need for concomitant quality of optical materials. One material, germanium, is extensively used in thermal imaging systems and has become the dominant material for the optical components of such systems. Optical grade germanium specifications do not exist in the Government-Industry complex and each lens system designer must independently specify the germanium characteristic and performance requirements. This paper briefly describes several performance characteristics of germanium which are based on a Government-Industry coordinated survey.
RAYTRAN infrared materials are formed by the chemical vapor deposition process which produces materials of unique characteristics and properties. This specification establishes optical and physical property requirements for polycrystalline zinc selenide and zinc sulfide made by this process.
This paper deals with physical, environmental, and some spectral requirements of thin film coatings of optical materials as found in MIL-C-675A MIL-C-00675B, MIL-0-13830A, MIL-C-13508C, MIL-C-14806A, MIL-C-48497- MIL-F-48616, and MIL-STD-810C.
I see that, according to the program, I am scheduled to deliver what is billed as "The Keynote Address". Normally, I would assume that the syllable "key" in keynote rather implies an operation analagous to the opening of a door, or perhaps providing a guide, to the program delights which are to follow.
Specifications are the communications link between customer and manufacturer. The lens manufacturing industry has voiced a need for a reference containing definitions of optical terms commonly used to write specifications. Such a dictionary is being compiled under the auspices of the American National Standards Institute.
In the practice of engineering, standards affect the communication of ideas and descriptions of items. Standards can be individually set, contractually defined, or set by industrial and professional organizations. This paper presents the role that the American National Standards Institute plays in developing an optical drawing practice standard.