Dependence of focal position on the microscale spherical lens imaging

•The position of the focal point of the microsphere can affect the super-resolution imaging property.•Microspheres with different material need different observing ways to get the best imaging quality.•The imaging results of different kinds of microspheres are different.

In this paper, hexagonal close-packed colloidal crystal samples are prepared by a self-assembly method. The image properties of three kinds of microspheres (silica, polystyrene and barium titanate glass) on the colloidal samples are studied. These microspheres are placed in air, semi-immersed and full-immersed in ethanol respectively. We find that all these microspheres can magnify the colloidal crystal samples and have the super-resolution imaging ability. Our experimental results indicate that the position of the focal point of the microsphere can affect the super-resolution imaging property, therefore microspheres with different material need different observing ways to get the best imaging quality. The silica microspheres and the polystyrene microspheres need semi-immersion, while the barium titanate glass microspheres need full-immersion to make the focal point close to the microsphere, so that the best imaging quality can be obtained. The mechanisms are also discussed with numerical simulations.