Understanding the sensitivity of optical systems thoroughly can lead to improved tolerancing and compensation. An examination into a complex sensitivity analysis is shown. This analysis is used to improve the overall tolerancing and compensation of an optical system. We have developed a tool to facilitate this method of sensitivity analysis. An example of a novel compensation method is presented.
Manufactured system performance analysis routines are built into several optical design software programs. These programs have limited abilities to change the probability distribution function of the tolerances. At Corning Incorporated, Advanced Optics, in-house analysis software is used which allows the distribution function of different tolerances to be customized. These simulation tools are capable of accurately modeling the distribution functions from the internal optical fabrication capabilities of Corning. This case study demonstrates the change in performance outcomes due to distribution functions and the importance of knowing the manufacturing distribution functions of the optical fabrication house used.
The manner in which an optical system is toleranced and compensated greatly affects the cost to build it. By having a detailed understanding of different tolerance and compensation methods, the end user can decide on the balance of cost and performance. A detailed phased approach Monte Carlo analysis can be used to demonstrate the tradeoffs between cost and performance. In complex high performance optical systems, performance is fine-tuned by making adjustments to the optical systems after they are initially built. This process enables the overall best system performance, without the need for fabricating components to stringent tolerance levels that often can be outside of a fabricator’s manufacturing capabilities. A good performance simulation of as built performance can interrogate different steps of the fabrication and build process. Such a simulation may aid the evaluation of whether the measured parameters are within the acceptable range of system performance at that stage of the build process. Finding errors before an optical system progresses further into the build process saves both time and money. Having the appropriate tolerances and compensation strategy tied to a specific performance level will optimize the overall product cost.
The tolerancing of lens systems has become more complex as system performance requirements tighten. The tolerancing of just the center thicknesses, surface radii, and surface irregularity are no longer sufficient for optical elements. This paper focuses on a new method to tolerance optical surfaces. There have been many papers written about different methods to tolerance optical surfaces which look to limit the artifacts left by different fabrication processes. The method proposed in this paper focuses on tolerancing to meet system performance, not the fight against the surface fingerprint of a particular fabrication process.
A thermal imaging zoom system has been developed for the mid wave infrared band with greater than 30X zoom range.
The zoom system provides continuous changes in the field of view from the narrow field of view to the wide field of
view. Athermalization was also a key feature included in the design. An active thermal compensation approach is being
used to cover a broad thermal range. A preloaded rail approach is used to maintain boresight and vibration requirements.
The final optical layout and mechanical design resulted in a system suitable for tactical and other harsh environments.
The current design is very compact for the extremely large zoom range but, the lens layout also provides adequate space
for folding. In this way the zoom system can be easily configured for applications with compact space claims such as
small turrets or gimbals. The fundamental optical design has also been found to be capable of accommodating different
camera formats (focal plane array size and F number).
Multiple fields of view are achieved by two methods. The system can have optical groups that flip in and out to change
the field of view, and/or optical groups that move axially to change the field of view. For flip in systems, the fields of
view are discreet and they may have greatly different fields of view. A zoom system can have a continuous change in
the field of view, but is often limited in the field of view range that can be achieved. Corning Incorporated has
developed a thermal imaging zoom system with greater than 30X zoom range. With a solid fundamental design and
appropriate selection of moving group focal lengths, the zoom system provides continuous changes in the field of view
from the narrow field of view to the wide field of view. Corning accomplished this result in a short package with just
two moving groups. The system is for the MWIR band.
A person lacking training in optical design programs may perform tasks using the design program's power. This paper addresses how API, with Windows Component Object Model, allows a person lacking understanding of the operation of the design program to run optical sensitivity routines.
The metrology community traditionally used fixed telecentric lenses to do optical measurement. The need to investigate varying fields of view led to the use of several fixed magnification lenses; this approach eventually yielded to zoom lenses. The majority of zoom lenses are designed to hold one set of conjugates constant, usually the object and the image. Such zoom lenses typically have the entrance pupil internal to the zoom groups; thus varying in position during zooming. By placing a stop external to the zoom groups, a constant entrance pupil position can be achieved. This idea can be extended to a telecentric stop position, and hence a telecentric zoom lens.