The Schneider 28mm f/5.6 Super Digitar XL Copal #0 is an ultra high quality wide angle lens designed to maximize the capabilities of adjustable cameras with sensor formats up to 6.0 x 4.5cm. The 28mm Super Digitar is expressly designed for digital imaging and discerning photographers who wish to use its large image circle to correct perspective and avoid image degradation in post-production.
The 28mm Super Digitar's full coverage of 115°/90 mm is reached at reached at f8 at which point the lens is free from mechanical vignetting. Schneider utilizes apochromatic correction of the 10 element double Gaussian lens design to achieve high contrast with an impressive resolution of 80 line pairs at f/8.
Double Gaussian Design
The double Gauss lens consists of two back-to-back Gauss lenses (a design with a positive meniscus lens on the object side and a negative meniscus lens on the image side) making two positive meniscus lenses on the outside with two negative meniscus lenses inside them. The symmetry of the system and the splitting of the optical power into many elements reduces the optical aberrations within the system.
Schneider employs apochromatic lens design to reduce chromatic and spherical aberrations that negatively affect performance.