

Achromat with a crown glass and a flint glass lens

Technical Information

An achromat with a positive refractive power consists of a convex crown glass lens with low dispersion (color splitting) and a concave flint glass lens with a high dispersion.



Comparison of the wavelength-dependent focal width change of a single lens and an achromat

The lenses are matched such that the variation of the focus position of the overall system is minimized for two selected wavelengths. A modern chromatic (color) correction of the focus position is calculated for the Fraunhofer lines C’ (479.9914 nm) and F’ (643.8469 nm). The remaining variation of the focus position (secondary spectrum), e.g. to the e-line (546.074 nm), is typically below 0.1% of the focal length.

In addition, the spherical aberration can be minimized by suitable geometry and material selections. LINOS achromats are especially well corrected against spherical aberration and are therefore very good for monochrome applications for optimum focusing and/or collimating with minimum wave front deformation, e.g. of laser light.

In the design of the LINOS achromats special attention was paid to the coma correction close to the axis (observance of the Abbe's sine conditions). This type of correction makes the system insensitive to slight tilting. This way, small, extended objects can be mapped very well.

Achromats are optimized for imaging remote objects. Therefore, they achieve their best imaging performance with light incidence parallel to the axis (e.g. focusing collimated laser radiation). Achromats are asymmetric; therefore one must observe a correct alignment in the beam path. Typically, the more strongly curved surface faces the parallel light.

All LINOS achromats are laser-centered and therefore have an excellent alignment of the center of curvature (optical axis) to the edge of the achromat. In combination with high demands on the surface shape, this ensures a constant high imaging quality. This optical imaging performance is subject of strict quality control. Typical wave front deformations are in a range between Lambda/4 and Lambda/10.



Poly- and mono- chromatic MTF curve for achromat with f = 200 mm / Ø 31.5 mm

The modulation transfer function (MTF) illustrates the high imaging quality. This type of graph shows the resolution capacity in dependence of the resolution of the object or image structure (also see the chapter "Technical Information on Optics ". The resolution is usually close to the theoretical diffraction limit.



Monochro- matic MTF curve for achromat with f=200 mm / Ø = 31.5 mm



Polychro- matic achromat with f=120 mm / Ø 25.4 mm



ARB2 Broadband- anti-reflective coating for VIS, Transmission for 450-700 nm > 99 %

LINOS achromats are available with two different coatings.

Both coatings are hard and scratchproof anti-reflex coatings.

Besides the ARB2 VIS for the visible spectral range, the selection of all microbench-compatible elements was supplemented with the ARB2 NIR for applications in the near infrared spectrum.

Please refer to the transmission diagrams for the characteristics of both coatings. One outstanding feature of both coatings is the high transmission of our achromats, which is >99% for the stated wavelength range.



ARB2 Broadband- anti-reflective coating for NIR, Transmission for 725-1200 nm > 99 %