In the measurement world there is a trade-off between the distance from the sensor and the accuracy of the measurement. This is caused due to the numerical aperture of the sensor’s objective lens. The numerical aperture, or NA , is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. The calculation is NA=n∙sinθ, where n is the index of refraction of the medium in which the lens is working (1.00 for air), and θ is the maximal half-angle of the cone of light that can enter or exit the lens.
In many fields the F-number (also written as f# or f/) is used instead, which describes the ratio of the lens’s focal length to the aperture diameter: f#=f/D
Put more simply, a lower f# denotes a greater aperture opening which allows more light to reach the image sensor. The f# cannot be smaller than 1.0 since the lens’s aperture diameter cannot be smaller than its focal length. The more light it collects the more information it receives, thus increasing the accuracy and precision of the measurement.
So if the objective lens aperture is a set diameter (and it usually is), and one needs a greater clearance distance from the sensor, it would be at the expense of the measurement accuracy. It’s a lot easier to change the focal length of the objective lens alone, rather than redesigning all the mechanics and optics of the sensor to create a larger lens aperture. This is also why more accurate sensors are much larger and bulkier than other sensors – mainly, due to the larger diameter of the collecting objective lens.
Optimet has overcome this challenge and created a new line of ConoPoint-HD sensors. Optimet’s unique Conoscopic Holography technology enables preserving the same focal length along with increased accuracy. But, due to laws of physics it has to come at the expense of depth of field, in our case – measurement range.
Another feature of the HD sensors is the small spot size which enables measuring with higher lateral resolution. As known, Nyquist’s law states that the sampling resolution cannot be smaller than half the spot size which is used for measurement.
If your application requires increased precision along with large standoff and higher lateral resolution the CP-10HD sensor is just for you.
|25mm lens||Standard sensor||HD sensor|
|Min. Lateral Resolution||14µ||6µ|
|Geometry||Hard Geometry, 3D objects||Micro mechanics, flat surfaces|
|Materials||Diffusive||Diffusive & Shiny|