The advent of large telescopes for remote sensing presents special challenges for optical testing, particularly for
verifying focal plane array alignment. If testing in air, the large well-enclosed telescope cavity can create air stagnation
or thermal gradient effects that can distort the optical wavefront unpredictably, resulting in noisy and inaccurate
measurements. Testing in vacuum presents instrumentation challenges but eliminates the air effects and provides
excellent data. This paper describes the experimental setups and compares through-focus test results for a large remote
sensing telescope when tested in both air and in a vacuum.
MTF testing of optical systems incorporating high-speed time-delay-integrate device (CCD) arrays has typically been a challenging task, more so than area or linear arrays. TDI imaging depends upon the synchronized motion of an image with the clocking of TDI lines. Simulating this motion often requires complicated and very precise mechanical equipment such as a moving belt or rotating drum. An alternative to this mechanical approach involves the use of a flashlamp to freeze the motion of an object during one of the TDI integration stages. This flashlamp method is straightforward and eliminates MTF errors due to velocity mismatch and scan misalignment. This paper describes the approach used to obtain sine wave and knife-edge images for MTF analysis using the flashlamp method. Test data and results for an instrument with a large aperture that is used in R and D for high-resolution space-based imaging is presented.
Illumination characteristics play an important part in machine vision inspection by making certain critical features conspicuous. Frequently, the angle of illumination can be of importance in enhancing the detection of features that have height or depth. The highlights or shadows produced by grazing-incidence illumination produce contrast differences that are easily detected by an appropriate vision system. This paper explores the role of this lighting technique in machine vision applications. Three examples are presented that describe the application of this technique on paper documents. In the first example, grazing-incidence is used to detect the presence of an erased signature on a forged personal check. In the second example, the technique is used to detect the presence of an address label on a piece of mail. In the third example, grazing-incidence is used to verify the impression signature of a financial document.
There is a serious need for a practical system to evaluate the nighttime visibility of existing traffic signs and provide data for making decisions on sign replacement. A mobile system has been developed which can measure the average retroreflectance of sign legend and background from a moving vehicle during daylight hours. This system uses a video camera to acquire sign images a xenon flash as a source of light a personal computer to analyze the sign images and a laser rangefinder to measure the distance to the sign.