The accuracy of OTF and MTF measurements of aerial cameras and photographs is discussed. Modulations for positions at 40° off axis have to be determined for the wide angle cameras commonly used in photogrammetry. Instead of sinusoidal test patterns, natural edges on the ground can be utilized in practical aerial photography. The particular problems concerning measurements of emulsions are dealt with. The possibility of utilizing photo interpretation results or photogrammetric measurements of ground details as an aid for establishment of a quality criterion for aerial photographs is discussed.
For many years the lens designer has been faced with the realization that the limiting criteria in lens performance could not always be attributed to his capabilities in theoretical design, but more to his ability to take into account the limitations imposed by the mechanical design and the skills and facilities available in manufacture. Modern high performance optical systems do not permit the lens designer the freedom of traditional designs in terms of tolerances and capacity to over design, to compensate for the subsequent loss of performance due to manufacturing techniques. The development of a method of lens element mounting more suited to the requirements of high performance lens systems, is described and analysed.
This paper considers the nature and magnitude of the influence of the spectral bandwidth on the relevant optical quality MTF of a night vision objective as measured during testing and quality control and its relationship to that which is "seen" during applications. The results show that the practical constraints placed on the quality control criteria may lead to MTFs which are widely different from that "seen" during applications. The origins of this difference are also discussed.
There are some kinds of optical and mechanical system for which particular emphasis is placed on obtaining the best possible geometrical accuracy. In the design of accurate mechanical devices the engineer usually has to choose between two different approaches - should he proceed according to so-called 'kinematic principles', or should he rely instead on 'averaging by over-constraint'? The same kind of choice can arise in the design of many types of optical system, and the virtues of the averaging approach are sometimes over-looked. Illustrations of this dual choice are taken partly from early work on the photographic manufacture of gratings and partly from current work on the optical micrometer.
The proposed method allows : the calculation of the optical transfer function without using classical surface smoothing method, the use of simple summation instead of surface integration. Furthermore, with this method, the transfer function can be easily used as a merit function for calculation improvement.
Lasers have increased the use of interferometers for optical testing and have changed the types that are used. Fizeau and Twyman-Green interferometers with classical sources remain useful for testing flats and flat-sided components, but complete systems are now most easily tested by new common-path interfero-meters and a laser source. Surfaces of unusual shapes can be tested by hologram interference.
Monitoring of high-volume lens manufacture for Polaroid Land photography requires an acceptance criterion which is both relevant to picture quality and suitable for automatic testing. In a hardware test based upon the Modulation Transfer Function, the problem is to choose what not to measure, while obtaining enough information about a lens to assign it a useful figure of merit. The predominant defects of manufacture are field tilt, resulting from tilting or decentering of components, and field curvature, from small errors in spacing, thickness, radius, or index. Field tilt and curvature are not "local" defects of the image surface, insofar as they may be removed by a local refocus. We therefore need a test procedure which can (perhaps simultaneously) examine image quality over an extended field, but which is principally called upon to evaluate focus differences. At multiple field locations a single-frequency modulation measurement adequately defines the MTF for the low spatial frequencies of interest, and can be interpreted easily in terms of the root-mean-square blur of the Point Spread Function. We will discuss the logic of 100% lens acceptance testing and two types of instrumentation we have used.
Optics has traditionally been regarded as something of a 'black art', practised by highly skilled operators using appallingly primitive tools and their own subjective judgement. However, this is becoming a thing of the past; modern requirements of high production or extreme accuracy are not consistent with a little understood production line, requiring operators to be trained for 5-10 years: The modern approach is to regard an optical component as a piece of specified material which must be treated in a straight-forward engineering fashion to produce the object on the drawing within specified tolerances and costs. To that end, the production process has been studied in great detail, from material selection through forming to polishing. But there are still anachronisms, in areas such as testing, edging, and final inspection. The whole business of test plating, with its huge stocks of expensive plates, and its risk of damage to the product seems to cry out for a rethink. Requirements of modern lens designs have shown the old methods of centring to be inadequate. Large percentages of product are being reworked or scrapped for lack of objective standards at the inspection stage, and knowledge of what is important, and in what context.
In response to the ever increasing demand on the quality and quantity of optical elements and systems and the economic pressures, there is increased reliance on instrumentation as a means for enhancing quality and productivity. The modern interferometer is ready to be assimilated into routine production and quality control operations. The types of measurements which such an instrument should be capable of performing, as well as its functions and features, are discussed. Specific examples are used to illustrate the utility, versatility and ease of use of a modern interferometer.
The image intensifier (1.1.) tube is used in devices for observation with the eye, the film camera or television camera of objects under poor illumination conditions. The tube is an electrostatically focussed electron lens with a cathode and an anode and between these two possibly one or more electrodes. The tension on the anode is positive with respect to that on the cathode and may vary between 12 kV and 45 kV, depending on the type of tube. The high voltage generator is included in the housing of the tube, or may be designed as a separate unit. The photocathode is a light sensitive layer, coated on the inside of the input window. The anode screen is a green phosphor layer deposited on the inside of the output window.
Infrared photodetectors having electrical outputs directly proportional to the radiant signal power input can be described in terms of specific and well defined parameters. These parameters and the associated measurement techniques are briefly outlined. Methods are suggested for extrapolating and interpolating from standard report data in order to prepare specific engineering information about expected operational detector performances. Some emphasis is placed on calculating a figure)/ v ss which gives a comparison of quantum detector's response to that of a "black" or "gray" detector for a given spectral content of incident radiant flux. The discussion contains information on current state-of-the-art detectors including those fabricated from the pseudobinary alloy semiconductors mercury-cadmium telluride and the lead-tin chalcogenides.
Three examples are given of outstanding electro-optical developments in which Quality Assurance played an important role. The first example is the ACS 1000, which is a sophisticated blood analyzer developed by the Medical Systems Center of Honeywell, Inc. Quality Assurance must be invoked for reliability, repeatability, accuracy, optical resolution, contrast and color fidelity of the TV displayed image as well as dependability of the cell-finding and auto-focus subsystems. The second example is the Laser CRT, which is an electronically scannable semiconductor laser device, produced by the 3M Company. Quality Assurance principles were required to insure excellent resolution and linearity as well as high writing speed. The CdS radiation (515 Dm) is confined to a 0.2 radian symmetric cone emitted from a 25μm spot. Among its applications is that of optically addressing holographic memories. The third example is the Award-Winning "HAT" or Head-Attached Television system, which is the product of Honeywell's Systems and Research Center. The function of HAT is to provide audio-video tape records of surgical procedures as seen from the surgeon's viewpoint and with his oral comments for documentary and teaching purposes. Quality Assurance is required to provide functional performance and to meet surgery standards.
Methods are presented which have been evolved in the authors institute for the development of optical instruments for use in spacecraft, with the aim of demonstrably assuring the quality of a corrplex product in away that can be sensibly implemented in a small scale organisation. Rather than specifying generally applicable organisational checks and controls on the development process, it is attempted to establish for any particular case with administrative type of precision what materially has to be done to establish acceptable confidence in the quality of the product. To this end already the conceptual design is broken dawn into a hierarchy of constituents. Apart from its bookkeeping functions, this breakdown in the structure of its hierarchy is to be regarded as a design for the process of realisation, supplementing the design in its conventional sense which defines the end point of the process. Product- and process design are related and elaboration of the latter can produce corrective feedbacks to the former. It also brings to light the uncertainities that have to be resolved in the development programme before starting to realise the final product. Generally these uncertainities are of the following kinds: a. will components, materials and processes be suitable b. will the concepts be suitable c. will the concepts be compromised or disturbed by system complexities d. will the means and methods to reach and verify quality be suitable. The development programme can be structured to answer such questions. It will consist of several "design stages". Within each stage one or more models will be realised. The models generally can be distinguished into types:
-Evaluation samples. Models without strict configuration and traceabilitycontrol to answer a.
-Development models. Partial models, however to best standards for .the constituent or aspect in question to answer mainly b.
-Engineering models. Models of full complexity but of relaxed quality to answer mainly c and d.
-Qualification models. Models of full complexity and full quality for a dress rehearsel of the complete process.
The breakdown designing the process of realisation then can be repeated for each model. For further clarity the work at each constituent level for each model can be distinguished into: theory, evaluation, design, deliveries, parts manufacture, assembly and test, tools and support equipment. A development programme structured in this way can be evaluated for its own merits and the documented results of the work can be compared to it by an informed person without recourse to a complex organisation.
UK Government policy is to place the maximum responsibility for quality control with Contractors whose quality arrangements meet safeguards required for the cost effective performance of the equipment supplied. The policy of the Directorate of Quality Assurance (Weapons) is to: undertake, in conjunction with other Authorities and using fully trained personnel, its full responsibility for the assessment of those Defence Contractors of its concern take effective measures to ensure that the contractual documents, drawings and specifications define fully the performance and quality levels required support the development of techniques or test equipments which will eliminate or effectively reduce, the subjective element involved in making a judgment of optical performance parameters or visual standards. In order that the British Forces and overseas customers purchasing UK equipment have fall confidence in the quality of military optical devices the credibility of the Directorates specialist quality assurance advice to Project Management must be well founded and maintained. It is our firm belief that this advice must come from staff having a sound basic training in quality engineering who continue to practise full and independent product audit using test equipment which is both comprehensive and maintained at a high standard of effectiveness.
There are many variables in the manufacture of an optical system which affect its final performance. Examples of these are: homogeneity, refractive index and dispersion of transmitting materials, thickness, radii of curvature and surface form of individual elements, relative separation, centration and tilt of assembled components etc. It is usual to exercise some degree of quality control at the different stages in manufacture but except in a few very simple types of system this is not sufficient to ensure that the final complete system will perform adequately. In general it is therefore necessary to carry out some form of testing on the assembled image forming system to check that the quality of the final image is acceptable. This applies equally well to optical as well as electro-optical systems.
The ACOFAM-MATRA is used in the laboratory. New and more simple equipments have to be developed for production testing. A new and simple program of test is proposed for the evaluation of lenses. The principle of the ACOMAT is given and its features are discussed.
The discussion which continually surrounds the subject of nonÃ¢â‚¬â€?functional defects on the surfaces of glass components in optical systems; "cosmetic defects" by British Standards definition would indicate that the problem of adequate specification and assessment of such defects is by no means satisfactorily solved. This particular contribution to the dialogue is in the form of a positive recommendation for a change in the method of specifying such defects in relationship to complete optical systems. The need for such a change arises from the inconsistancies which occur from the use of methods which provide for component assessment only and which attempt to define subjective defects by objective criteria and which have grown from the use of inspection methods more suited to dimensional parameters. I have considered for some time that the general principles of quality control and assurance now being practised allow a method of assessment which is more suited to the subjective nature of the defects under consideration. This presentation of these recommendations at the 1975 International Conference on Quality Assurance in Optics is made to put forward my thoughts in order to determine the extent of support for changes along the lines proposed.
Though measurement of the Modulation Transfer Function (MTF) has become a practical technique for the evaluation of optical systems much useful testing work can still be done with an interferometer, espec-ially in the examination of components. Interferometer tests, which display the wavefront aberrations, can readily be used in the testing of optical components and sub assemblies but can be difficult to set up for testing complete telescopic sighting systems. MTF tests, which give a quantitative measure of the imaging performance of an optical system, can be used for sights, but for MTF to be effective parameters of tests must be carefully defined. Features of the test apparatus and procedures to enhance the reliability, ease of execution and effectiveness of tests are discussed. A simplified MTF test apparatus operating at a single spatial frequency scanning through all azimuths permits the use of concise MTF criteria for specification and quality control purposes; additionally in on-axis tests the dioptre setting of fixed focus eyepieces may be checked and in off-axis tests field curvature and astigmatism evaluated.