Genie Nano-CL Series™ Additional Reference Information • 95Additional Lens Parameters (application specific)There are other lens parameters that are chosen to meet the needs of the vision application. Theseparameters are independent of the Nano model (assuming that the Lens Mount and Lens SensorSize parameters are correct, as previously covered in this section). A vision system integrator orlens specialist should be consulted when choosing lenses since there is a trade-off between thebest lenses and cost. An abridged list of lens parameters follows – all of which need to be matchedto the application.• Focal Length: Defines the focus point of light from infinity. This parameter is related to theNano mount (C or CS mount). See Genie Nano Specifications — Back Focal Distance.• Field of View: A lens is designed to image objects at some limited distance range, at somepositive or negative magnification. This defines the field of view.• F-Number (aperture): The lens aperture defines the amount of light that can pass. Lensesmay have fixed or variable apertures. Additionally the lens aperture affects Depth of Fieldwhich defines the distance range which is in focus when the lens is focus at some specificdistance.• Image Resolution and Distortion: A general definition of image quality. A lens with poorresolution seems to never be in focus when used to image fine details.• Aberrations (defect, chromatic, spherical): Aberrations are specific types of lens faultsaffecting resolution and distortion. Lens surface defects or glass faults distort all light orspecific colors. Aberrations are typically more visible when imaging fine details.• Spatial Distortions: Describes non-linear lens distortions across the field of view. Suchdistortion limits the accuracy of measurements made with that lens.Optical ConsiderationsThis section provides an overview to illumination, light sources, filters, lens modeling, and lensmagnification. Each of these components contribute to the successful design of an imagingsolution.IlluminationThe amount and wavelengths of light required to capture useful images depend on the particularapplication. Factors include the nature, speed, and spectral characteristics of objects being imaged,exposure times, light source characteristics, environmental and acquisition system specifics, andmore. The Teledyne DALSA Web site, http://mv.dalsa.com/, provides an introduction to thispotentially complicated issue. Click on Knowledge Center and then select Application Notes andTechnology Primers. Review the sections of interest.It is often more important to consider exposure than illumination. The total amount of energy(which is related to the total number of photons reaching the sensor) is more important than therate at which it arrives. For example, 5mJ/cm 2 can be achieved by exposing 5mW/cm 2 for 1ms justthe same as exposing an intensity of 5W/cm 2 for 1ms.
