Within the visible spectrum, black and white image analysis is the most effective in blue light. Vision & Control’s Blue Vision series lenses are specially designed for this spectral range and offer maximum definition and the greatest possible depth of focus.
Image definition and depth of focus are two optical parameters that unfortunately counteract each other. The more you reduce a lens, the more blurred the image due to diffraction. However, industrial image processing requires both maximum definition and as much depth of focus as possible. The newly developed “Blue Vision” lens series meets these requirements. To do this, Thuringia-based opticians take advantage of the fact that the intensity of diffraction depends on the wavelength. If a specific lens with an aperture of f / 10 creates an aerated disc with a radius of 8 µm under red light (650 nm), then the disc only has a size of 5.5 µm under blue light (450 nm), which reduces blurring by almost a third. It is therefore logical to think that accurate analysis of images under blue light should be carried out whenever possible: Deep Blue LEDs in particular have an extremely high level of effectiveness.
It is true that it would be false to believe that lenses that have not been color-corrected could be used for monochromatic analysis. Blue LEDs have a total width in the middle of the maximum (FWHM) of 20 nm to 30 nm. This can lead to transverse chromatic aberrations that change the reproduction scale, as well as axial chromatic aberrations that misalign the focus. For example, a non-color-corrected lens with a reproduction scale of 0.2 and a lens field diameter of 15 mm creates a 10 µm fringing effect at the edge of the image if the wavelength varies by 20 nm. Therefore, the image is blurred and additional axial chromatic aberrations also make the center of the image more blurry.
For lenses that cover the entire spectrum of visible light, color correction is complex and particularly prone to errors in the blue light region (450 – 480 nm) of all places. Therefore, the color correction for Blue Vision lenses is specifically set in the blue spectral range at 470 nm. As a result, only extremely small axial chromatic aberrations of less than 10 µm, below the detectability threshold, occur between wavelengths of 450 and 490 nm. The distortion of this lens is less than 1%.
At present, the range consists of four telecentric lenses, each with a lens field diameter of 18 mm and 30 mm. The reproduction scales of the individual models were chosen so as to cover all prevailing sensor sizes. In each case, this produces an image field diagonal of 4.1 mm (1/4″); 6.1 mm (1/3″); 9 mm (1/1.8″) and 11 mm (2/3″).
Suhl developers gave particular importance to a compact design. So the T18 / 0.23 is just a little longer than a conventional endocentric lens. Although the lenses have maintained Vision & Control’s aerodynamic design, the thickness of the tube walls has been designed so that the lenses can withstand harsh industrial use.
All lenses have an adjustable aperture. From aperture f / 8 to f / 11 (depending on model) are limited by diffraction and, as a result, are also suitable for 5 megapixel sensors. For use in extreme conditions, Blue Vision models are also available in shake-proof versions with a fixed aperture and glued lenses.
The T18 series has a lens tube diameter of 28 mm (30.5 mm aperture ring) and can be locked to this size. The T30 series lenses have a thickness of 42mm at the front only, but otherwise have the diameter of the T18 series so there is room for them in the same brackets. Suitable lens mounts are available.
As the Blue Vision series has been specifically optimized for blue light, its lenses are only suitable for red light or even infrared light up to a limit. That’s why Vision & Control developers are already working on a series of lenses for this spectral range.