Data from: Optical design of an inner focus type Telephoto lens with a large aperture

As consumer demand for high-performance lenses increases, lenses with a
bright aperture of F/1.2 are being developed in the AF market. As the F/#
decreases, the diameter of the lens increases, which increases aberration
as well as the weight of the lens. Those used in ordinary cameras must be
very small and thus have relatively weak torque. Although motors with
stronger torque such as ultrasonic motors are available, they generate
noise when the lens moves, which is fatal in filming video content. To
solve this problem, a design using a floating system that moves two lens
groups has also been proposed. However, this becomes more complicated in
terms of mechanical and electronic control compared to the method of
moving a single lens group. Therefore, in this study, we propose a novel
design for an F/1.2, f=85 mm large aperture telephoto lens that utilizes
one AF group and consists of a single lens to lighten the moving lens
group for quiet and precise focusing. Even at the maximum aperture of
F/1.2, the modular transfer function (MTF) performance was maintained at
80 % in the center and 69 % at the periphery. By reducing the weight of
the moving lens group by using a single focusing group, the proposed
system was able to operate quickly and quietly without any significant
degradation in performance even in the MOD area. Therefore, our results
demonstrate that an internal focusing structure based on a single focusing
group is feasible even in an F/1.2, with an 85-mm large-aperture prime
lens.