Meridian® Starfield Mounting Scheme
A Meridian Starfield assembly is a rigid assembly of multiple target projectors that together cover the entire field of view of the DUT by projecting test targets from all desired field angles. Target projectors used in a Starfield assembly may either be of the fixed focus type in which the apparent object distance is factory set, or they may be Focusing Target Projectors, or a combination of both types. Different focal length projectors are available to suit the focal length of the DUT. Each projector contains a microcontroller, factory calibration data, and a unique address making it possible to remotely query and control the brightness of any given field point. All illumination is provided by white LEDs which are driven in a linear manner in order to avoid any flicker issues. A range of color temperature white LEDs is offered, and NIR illuminators are available on request.
The Meridian Starfield mount consists of a thick plate into which precision bores are machined to receive the target projector barrels. This allows for consistent and repeatable testing of field points. When provided with a customer’s camera lens prescription or black box model, Optikos can design unique targets to compensate for high distortion field points for ultra wide FOV cameras.
If the set of field angles required by a customer cannot be satisfied from our library of existing Starfield designs, we will work with the customer to design one specifically tailored to their needs. This includes specifying the mechanical interface, the selection of focal lengths and targets for the projectors, and configuring them so as to minimize the working distance to the DUT. We have developed special software to analyze projector configurations to ensure that there is no vignetting of the target, and to determine the size and shape of the target pattern in the image plane of the DUT.
Measurements may be made with Meridian® Prime software, or may be integrated through library calls with customer software, and include:
- Simultaneous horizontal and vertical MTF measurements at multiple field points in a single frame
- Geometric imaging parameters
- Camera Line of Sight (LOS) tip-tilt relative to camera housing (Requires alignment of DUT nest to Starfield)
- Camera roll angle relative to camera housing (Requires alignment of DUT nest to Starfield)
Starfield assemblies are also increasingly being used by customers in active alignment setups, especially for wide field camera assemblies in which the need to balance the imaging performance across a wide range of field angles frequently requires a more sophisticated approach than simply back illuminating printed targets.
Target projectors in a Starfield assembly are daisy-chained together with a Power+RS-485 bus architecture. Each assembly ships with a control box with power and USB inputs that creates the RS-485 and power connector interface. High reliability Lemo® connectors are used throughout.
Meridian® Arch Mounting Scheme
The primary advantage of the Meridian Arch mounting scheme is that it consists of just two different types of machined plates (one top plate and four identical wings) each of which may be fabricated using a 3-axis CNC milling machine. This makes CAM programming time relatively short and the qualification of the machining program largely unnecessary. All of the positioning accuracy in these plates arises from the planarity of a single surface and the locational accuracy of several dowel pins.
The Arch assembly is a textbook example of exact constraints. It uses the barrel of the center target projector to locate each of four wings that radiate out along the diagonals or the cardinal directions of the field of view. Each wing holds the required number of projectors, each of which is located on the wing by being pulled into the corner established by the plane of the plate and two dowel pins. Tangency to these features and the roundness of the tightly-toleranced projector barrel are sufficient to accurately locate the field angle for each projector. The radial directions of the four wings are set by the locations of dowel pins pressed into the top plate.
The Meridian Arch mount is well suited to customers who require just a few projector assemblies or to those customers who need a test setup for evaluation purposes or production use with the shortest possible delivery time.