A mathematical approach for the third order solution for a general zoom lens design is proposed. The design starts with a
first-order layout. Lens elements with the proper refracting power are placed at the proper distances to meet the physical
constraints of the intended lens system. For the third-order design stage, a matrix notation called "Aberration
Polynomial," which clarifies the linearity of the transformation from a normal thin group configuration to a general thin
group configuration by pupil shift and conjugate shift theory is implemented.
The purpose of the method is correcting low-order aberrations during the preliminary design of zoom lenses. The goal is
to mathematically reduce to zero the four aberration coefficients of the third-order (spherical aberration, coma,
astigmatism, and distortion) rather than searching for a minimum by commercial design software. Once this theory is
proven and accepted, it becomes possible to determine how many groups are needed for a particular optical system. The
method of aberration polynomials establishes the number of groups needed to correct a given number of aberrations at a
given number of zoom positions. Furthermore, it provides the shape or bending of the elements, from where it will be
possible to continue to optimize with standard methods.
Zoom lenses are usually designed for a specified waveband and change magnification, and thus resolution, for different object sizes or different object distances. However, the Advanced Technology Solar Telescope (ATST)/ Visible Light Broadband Imager (VLBI), under development by the National Solar Observatory, require constant resolution for different wavelengths over a wide spectral range (388.3 nm 3o 854.2 nm). An eight-element zoom lens meeting this requirement is presented, and yields diffraction-limited performance over the field of view at nine specific wavelength/zoom positions. Each zoom position, corresponding to a specific wavelength, has a focal length and f/number for achieving constant CCD sampling. The Strehl ratio of the telescope is greater than 90% over all zoom positions.
This poster outlines the conceptual design of the Visible-light Broad-band Imager (VBI) instrument for the Advanced Technology Solar Telescope (ATST) as it follows from scientific requirements. The VBI is scheduled to be the first-light instrument of the ATST, highlighting the telescope's high spatial resolution capabilities.