Figure 1. Overview of compared filters.

The outline images show a photograph of the track-etch filter, the microsieve and the transmission electron microscopy (TEM) grid. The perforated area of each filter is indicated in red. The microsieve contains perforated horizontal bars alternated by support bars, giving rise to the horizontal pattern. The detail shows dark field images for the three filters. Spacing of the pores is random for the track-etch filters, leading to occasional double pores. Microsieves and TEM grids have periodical pore spacing.