Designed to give maximum performance at full aperture with superior control of flare, distortion and spherical aberration, the 5/i Primes from Cooke feature an industry first - dimmable backlit focus scale for effortless viewing in all conditions. The 5/i Primes feature the same excellent build quality we've all come to expect from Cooke given their 100+ years of motion picture lens design and manufacturing. Among the fastest prime lenses ever offered by Cooke, the 5/i Primes offer an excellent balance of image quality and maximum aperture. All Cooke 5/i prime lenses have a common front diameter of 110mm and consistent focus and iris gear position and diameter ( With exception of the 135mm lens with a 136mm front diameter)