Optimized for blue light

Image sharpness and depth of field are two optical parameters that unfortunately work against each other. The more you stop down a lens, the blurrier its image becomes due to increasing diffraction. Nevertheless, industrial image processing demands both: maximum sharpness with the greatest possible depth of field. The newly developed lens series "BlueVISION" meets this demand. Our optics developers take advantage of the fact that the intensity of diffraction depends on the wavelength: if a specific lens at f-stop 10 produces a diffraction disc with a radius of 8 micrometres with red light (650nm), then with blue light (450 nm) it is only 5.5 micrometres in size, which means that the blur is almost a third less. It is therefore obvious to carry out precise image examinations with blue light wherever possible, especially since blue light-emitting diodes (deep blue) have an extremely high degree of efficiency.

Of course, it is a fallacy to believe that lenses that are not colour-corrected can be used for monochromatic examinations. Blue LEDs have a half-width of 20 nanometres to 30 nanometres. This creates both lateral chromatic aberrations, which change the magnification, and longitudinal chromatic aberrations, which shift the focus. For example, an uncorrected lens with a magnification of 0.2 and an object field diameter of 15 millimetres will produce colour fringes 10 micrometres wide at the edge of the image if the wavelength varies by 20 nanometres. This makes the image look washed out and additional longitudinal colour aberrations also make the centre of the image blurrier.

With lenses that cover the entire range of the visible light spectrum, colour correction is complex and particularly error-prone in the blue range (450 nm - 480 nm). The colour correction of the Blue Vision lenses therefore starts especially in the blue spectral range, at 470 nanometres. As a result, only extremely small longitudinal colour errors of less than 10 micrometres occur between 450 nanometres and 490 nanometres, which are below the detection limit. The distortion of these lenses is less than 1%.

The series currently consists of four telecentric objectives each with object field diameters of 18 millimetres as well as 30 millimetres. The image scales of the individual models have been chosen to fully cover all common sensor sizes. This results in field diagonals of 4.1 mm (1/4"); 6.1 mm (1/3"); 9 mm (1/1.8") as well as 11 mm (2/3").

Our lens designers placed special emphasis on a compact design. The TO18/0.23, for example, is only slightly longer than a conventional entocentric lens. Although the lenses have a slim Vision & Control design, the wall thickness of the tubes is still such that the lenses can reliably withstand rough industrial use.

All lenses have an adjustable aperture. From f/8 to f/11 (depending on type) they are diffraction limited and therefore also suitable for 5MP sensors. For use in extreme conditions, Blue Vision models are also available in vibration-resistant versions, with fixed aperture and bonded lenses.

The TO18 series has a tube diameter of 28 millimetres (aperture ring 30.5 millimetres) and can be clamped at this circumference. The TO30 series lenses are only 42 millimetres thick in the front part, but otherwise have the same diameter as the TO18 series, so they fit in the same holders. Corresponding lens holders are available.

Since the BlueVISION series is specially optimised for blue light, its lenses are only conditionally suitable for use with red or even infrared light. Our developers are therefore already working on a lens series for this spectral range.