Combining optical performance, mechanical robustness and complexity management in a single multispectral optical system: this is the challenge taken up by PISÉO with the visible-NIR-SWIR zoom.
Developing a multispectral optical zoom covering the visible (VIS), near-infrared (NIR) and short-wave infrared (SWIR) is a major technological challenge. Few companies are able to combine optical performance, mechanical robustness and industrial viability over such a broad spectrum.
PISÉO has demonstrated this with a multispectral continuous zoom project, illustrating its unique know-how in the design of complex optical systems, while meeting demanding specifications: precise numerical aperture, continuous x15 zoom factor, strict control of maximum authorized distortion, high MTF (Modulation Transfer Function: the system’s ability to reproduce fine details with contrast), while respecting constraints on size and field-of-view (FOV/DOV, i.e. the extent and depth of field of the observable scene).
Chromatic correction across a broad spectrum
Controlling chromaticity across a spectral range from a few hundred nanometers to more than one micron, without resorting to fragile fluorite glasses, required in-depth research into optical material combinations. Thanks to bibliographic and simulation work, PISÉO has selected special glasses that are transparent over the entire visible-NIR-SWIR spectrum, optimizing their dispersion for quasi-apochromatic – correcting out-of-focus errors across three or more wavelengths, consistent with numerical aperture and image quality constraints.
Controlling geometric aberrations
The system had to maintain parfocality – the ability to maintain focus when changing focal length – between the visible, NIR and SWIR channels, despite their natural focusing differences, throughout the entire focal range. The integration of aspherical lenses has made it possible to effectively correct spherical aberrations, coma – the comma-shaped distortion of light points at the edge of the image – and astigmatism without multiplying the number of optical elements.
The result: a compact, high-performance system that respects space constraints and produces sharp images across the entire field, with controlled distortion.
Mechanical and compactness constraints
The zoom lens featured synchronized moving groups, with a high zoom ratio (x15), imposing significant mechanical constraints. PISÉO optimized the number of moving groups and types of movement, while anticipating manufacturing limitations: choice of lenses available from suppliers, limitation of costly aspheric surfaces, reduction in the variety of materials to simplify sourcing and guarantee manufacturability, while maintaining the expected MTF performance.
PISÉO mobilized the powerful tools of Zemax OpticStudio, one of the world’s leading optical design software packages. This ray tracing tool was used to simulate and optimize every parameter: curvatures, thicknesses, spacings, indices, spectral performance, FOV/DOV and MTF quality, in multispectral and with parfocality.
A single file allows simultaneous analysis of different focal lengths and spectral bands, facilitating iteration, archiving and optimization.
The design followed a complex process: firstly, the system was preliminary design to select a robust optical combination (balancing the groups to ensure feasibility), then aberrations in each group were corrected, and finally achromatization was carried out, again by sub-assembly, using a selection of lenses to cover the entire target spectrum.
Once the system was complete, a further optimization phase was carried out to find the best compromise between complexity and performance (curvature, thickness at center or edge, bonded or unbonded elements, diversity of lenses, etc.).
This meticulous optimization phase led to a high-performance theoretical system, which PISÉO then made realistic through tolerancing studies, in order to further reduce the points of sensitivity of the assembly or arbitrate between variants: statistical analysis of the variations expected in production, to guarantee that a real product would remain compliant with requirements, even taking into account manufacturing and assembly margins.
This zoom lens was to be mounted on maritime or aeronautical platforms, for long-distance observation: obstacle spotting, area surveillance, defense equipment. These applications called for a product that was robust (no fragile lenses), compact (integrated into an optronic ball), and ultra-high-performance (resolution, image sharpness and controlled distortion across the entire spectrum). The wide spectral range enables long-distance tracking, thanks to the reduced scattering of the atmosphere in SWIR, as well as identification (through combination with visible light).
Where others have failed to meet our customer’s needs, PISÉO has found innovative solutions, thanks to:
Their partners specialized in the manufacture of complex lenses for wide spectral ranges.
The opto-mechanical design skills of its engineers
Their in-depth mastery of software tools and optimization methods.
Their ability to take industrial constraints and integration aspects into account right from the design stage.
PISÉO is a recognized partner for the development of complex optical systems, able to intervene at every stage: from initial idea to market-ready product. Working with PISÉO means benefiting from rigorous support, cutting-edge expertise and the ability to transform technical challenges into concrete, reliable solutions.