Comment on ‘Super-resolution microscopy by movable thin-films with embedded microspheres: Resolution analysis’ [Ann. Phys. (Berlin) 527, 513 (2015)]

This work addresses the shortcomings of the recent paper by Allen et al. [Ann. Phys. (Berlin) 527, 513 (2015)], in which the authors attempted to quantify the spatial resolution and magnification in imaging by using microsphere-embedded films. Their methodology in resolution and magnification analyses is ill-considered and worth discussing. Neglecting the impact of the confocal arrangement, used for imaging in their work, on the resolution improvement factor has led to an exaggerated claim of ∼λ/6 as the inherent resolution gain of the microsphere. However, this ∼λ/6 value cannot be solely attributed to the microspheres because, the effects the pinhole function and image acquisition process of the laser scanning confocal microscope must be separated from their results in order to find the inherent resolution gain of the microsphere. The magnification analysis is flawed for several reasons: invalidity of geometrical optics for micron-scale spheres, neglecting the impact of the index of the PDMS film surrounding the microsphere, and the cyclic methodology used in presenting the magnification results. Specifically, such large claimed gaps between the object and the microsphere as a mediator of near-field information contradicts the coupling condition requirement, as claimed by the authors, between the scattered evanescent field of the object and the microsphere.