Optoliner Collimator (OC)
The OC group comprises several types of test pattern projectors that test TV cameras through the cameras' own imaging lenses unlike the standard OCs that project test pattern images directly onto the image sensors after the removal of the cameras imaging lenses. In optical terms, standard OCs are finite conjugate systems, whereas all OCs project images at infinity. A typical test setup sets the imaging lens of the TV camera at infinity. OCs are especially helpful where, for one reason or another, the camera lens is mechanically captive to the TV camera or where its removal is difficult, impractical or impossible. Typical examples are some of the low-end surveillance cameras and almost all gun cameras used on HUDs. OCs find use in permanent test setups where large volumes of TV cameras go through a test cycle to verify camera adjustment and alignment parameters such as image centration, resolution, focus, white balance, color balance, gamma and others.
Davidson Optronics provides two different OC approaches to cover the entire range of camera imaging lenses from wide angle to telephoto. The simpler one-step approach covers the longer focal length camera lenses, while shorter focal lengths require the more elaborate two-step approach.
For comparison purposes, Figure 1 diagrams the operating principle of the standard OC projecting the test pattern image directly onto the camera's image sensor.
The one-step method OC depicted in Figure 2 projects a collimated image into a camera lens having a focal length of 30 mm or more. This method utilizes commercially available 35 mm still camera lenses to project collimated images directly from the standard OC test pattern into the imaging lens and camera. This system employs only the integrating sphere illumination system and the housing for the filters and test pattern holder. An adapter with the proper interface for the lens attachment (usually a bayonet mount) completes the instrument. Mounting any fixed focus or zoom imaging lens renders the one-step OC ready for operation.
The two-step method OC shown in Figure 3 is the approach used for wide angle TV camera lenses having focal lengths of 25 mm and less. A collimated image from a regular lens would cause severe vignetting because it would not be able to fill the entrance pupil of the wide angle camera lens. The wider the angle and the shorter the focal length of the camera lens, the more severe this vignetting would be. The solutions to this dilemma involve the use of a series of lenses whose exit pupils are located outside the physical lens body. Combining such a lens with a standard OC projector creates an effective image collimator. The OC must be positioned very closely to the camera lens such that the projector exit pupil falls inside the camera lens.
Figure 4, which substitutes an eye loupe with the collimating lens and replaces the camera with the human eye provide a simple means of visualizing the underlying principal of this method. Fortunately, if the user already possesses a OC projector, the required collimator attachment can be supplied by Davidson Optronics and field retrofitted by the customer with no additional alignment or calibration required. Focusing (and size adjustment with the "V" models) of the pattern image upon the sensor is achieved through the OC projector focus mechanism.
There are practical limitations to both OC approaches described above. Obviously, OCs are not suitable for extremely wide angle lenses (fish eye lenses). In the one step approach, the collimator focal length is always larger than that of the TV camera lens and therefore, cost may limit the maximum practical focal length of the collimator lens. Even though the two-step approach provides more flexibility in the selection of a suitable combination of OC formats and collimator lens focal lengths, the number of readily available collimator lenses limits the selection. However, Davidson Optronics will design and manufacture custom optics for any unusual application or special customer test setup.
Although the standard OC system's Model K-4000 Multi Purpose Meter and Power Supply may be used with OCs, a simplified power system featuring manual voltage control and a panel meter displaying output voltage is available to supply power to OCs' illumination system. Please see the separate Model K-4010 data sheet.