The principle of DO at its simplest is cutting up the optics in perfectly circular rings, which are perfectly centered around the optical axis, removing the excess of glass for each ring, to just allow for the refraction required, and put everything together again, thus making a much flatter and lighter lens element possible.
In real life the construction is done without cutting up the lens element, often by using a synthetic material, like acrylic or something similar, and casting it. In order to avoid any dust gathering in the circles, it tends to be embedded in a matrix of another synthetic/plastic, with a different refractive index.
Rather complex, difficult to manufacture, and difficult to design due to different wavelengths having different refractive indices, which creates havoc, in principle, especially on or at the edges of each circular structure.
In a way, it is a fresnel lens, but not to create an evenly illuminated area, but to use as a real lens element.
HTH, kind regards, Wim
In real life the construction is done without cutting up the lens element, often by using a synthetic material, like acrylic or something similar, and casting it. In order to avoid any dust gathering in the circles, it tends to be embedded in a matrix of another synthetic/plastic, with a different refractive index.
Rather complex, difficult to manufacture, and difficult to design due to different wavelengths having different refractive indices, which creates havoc, in principle, especially on or at the edges of each circular structure.
In a way, it is a fresnel lens, but not to create an evenly illuminated area, but to use as a real lens element.
HTH, kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....