Within the visible spectrum, monochromatic image examinations with blue light are the most effective. The lenses in Vision & Control's Blue Vision series are specially designed for this spectral range and deliver maximum sharpness with the greatest possible depth of field.
If a specific lens produces a diffraction disk with a radius of 8 μm at f/10 with red light (650 nm), then with blue light (450 nm) it is only 5.5 micrometres in size, meaning the blur is almost a third smaller. It therefore makes sense to carry out precise image examinations with blue light wherever possible, especially as blue light-emitting diodes (deep blue) have an extremely high degree of efficiency.
However, it would be wrong to use lenses that are not color corrected for such monochromatic examinations. Blue LEDs have a half-width of 20 to 30 nm. This results in both lateral chromatic aberrations, which change the image scale, and longitudinal chromatic aberrations, which shift the focus. For example, a color uncorrected lens with an image scale of 0.2 and an object field diameter of 15 mm produces 10 μm wide color fringes at the edge of the image if the wavelength varies by 20 nm. This makes the image appear washed out and additional longitudinal color errors also make the center of the image blurrier.
The color correction of blue vision lenses is particularly effective in the blue spectral range, at 470 nm. This results in extremely small longitudinal color errors of less than 10 μm between 450 nm and 490 nm, which are below the detection limit. The distortion of these objectives is less than 1%.
The series consists of four telecentric objectives with object field diameters of 18 mm and 30 mm. Particular emphasis was placed on a compact design. Nevertheless, the wall thickness of the tubes is designed so that the lenses can reliably withstand rough industrial use. The Blue Vision lenses are only suitable for use with red or even infrared light to a limited extent. The developers at Vision & Control are therefore also working on a lens series for this spectral range.
