Both the Arch and Starfield mounting schemes may be designed to accommodate a number of different target projectors. These projectors consist of precision cylindrical barrels that house projection optics, the target reticle, and an illuminator. Each target projector is factory set to the required conjugate and the center of the target reticle is precisely bore-sighted to the outer barrel. Furthermore, targets with inherent orientations, such as crossedge targets, are aligned about the optical axis with respect to an external feature so that the roll angle of the target may be mechanically set when inserting the projector into the mounting assembly.
The illuminators are generally based on surface mount LEDs; either visible monochromatic, white LED, RGB, or infrared monochromatic depending on the customer’s requirements. Each illuminator circuit board includes a microcontroller for setting and monitoring the LED current and for providing a remote serial interface to each illuminator. By assigning a unique node address to each illuminator and daisy-chaining them together, illuminators may be remotely turned on and off at will and the brightness of each of the illuminators can be individually set.
Meridian® Focusing Target Projector (FTP)
The Meridian series of FTPs is a growing collection of miniature target projectors in which the apparent object distance and brightness of the projected target may both be set remotely. Besides their routine use in both Meridian Starfield assemblies and on the Meridian Flex platform, these projectors also find application in standalone test setups.
The FTP provides a convenient means of placing a virtual standard target over a wide range of apparent object distances in a compact space. This functionality enables the test engineer to perform testing over a range of conjugates and to perform through-focus resolution testing of fixed-focus cameras in a compact space. Through-focus data acquired in this manner and which reports the object distance at which the DUT is actually focused can provide important statistical process feedback to active alignment operations.
Focusing Target Projectors are offered in several different focal lengths and with a choice of different color temperature white LED illuminators. All units are factory aligned and calibrated, and all calibration information is stored in the device. The standard target used in the FTPs is an orthogonal “Crossedge Target” but other target geometries are available. Our engineers are always ready to discuss your particular testing requirements and to make appropriate recommendations. In fact, it is generally a good idea to consult with our engineers regarding the applicability of any given projector for a particular testing requirement. By their very nature FTPs are projectors of extended objects, so they may not be diffraction limited across their entire field or over the full aperture. The clear aperture is sized to prevent vignetting at a given distance, but in a test system it is the entrance pupil of the DUT that serves as the system stop. We will assist in selecting an FTP that does not itself contribute significantly to the measured MTF.
The robustness of the FTP design is assured by the incorporation of linear output encoders and special guide assemblies. The patent-pending drive scheme also enables us to achieve a high degree of straightness of travel of the center of projected target.