Variable-focus lenses enable dynamic focus control and reduce the volume of the optical systems. However, few of them have been scaled up to large apertures of 10 mm, which limits their application scenarios. Here, a variable-focus lens prototype with a 42 mm large aperture based on the liquid-membrane-liquid structure was proposed and evaluated. The prototype shows a range of adjustable optical power at [−3 D, +3 D], and demonstrates high repeatability during the operation process. The average normalized modulation transfer function value for an imaging system shows 0.7904 in 17.204 lp/mm and 0.5439 in 34.409 lp/mm. The resolution values in horizontal and vertical directions are 8 lp/mm and 8.98 lp/mm, respectively. Besides, the millisecond-level response time of the prototype is achieved with a rising edge of 5.02 ms and a falling edge of 3.66 ms. The prototype demonstrates the application scenarios of variable-focus lenses for large aperture requirements with the potential for satisfactory performance, such as in wearable devices, machine vision systems, and so on.