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Due to the properties of super-narrow focusing and super-resolution imaging, microsphere lens has attracted many attentions. In order to operate the microsphere lens freely, a microsphere holder is necessary to control its 3-D motions accurately. In this paper, a stable and practical microsphere holder is designed for microsphere lens scanning imaging. Furthermore, we numerically analyzed the influence of microsphere holder on the focusing properties of microsphere lens. With the reflections from the surface of microsphere holder, the wavefront in microsphere could be reconstructed through the interference between the incident light and reflection beams. At proper conditions, the curvature radius of incident wavefront in microsphere could be enlarged by the reflections beams, which could generate longer focal length of microsphere lens. Meanwhile, the width of focal spot is almost constant, which is as narrow as the one without microsphere holder. Therefore, the microsphere holder will almost not reduce the imaging resolution of microsphere lens, but enlarge its working distance obviously, which is significant for microsphere assisted far-field super-resolution imaging. Through the optimization of the opening angle and the material of microsphere holder, an ultra-long working distance of 6.5λ has been achieved by microsphere lens with a proper microsphere holder. This holder could be applied for microsphere assisted far-field super-resolution imaging due to its contribution on microsphere lens control and focal length increase from near-field to far-field, and extend the applications of microsphere assisted nano-imaging into more fields and more samples.
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