Glass micro-pore optics technology, developed over the last years for planetary X-ray imagers, has
been used to assemble optical modules in approximation of a Wolter-I configuration. These tandems of
glass sectors consist of hundreds of square, millimetre sized, multi-fibres that each contain more than a
thousand, 3 μm thin, X-ray mirrors with a surface roughness suitable for application at medium X-ray
energies. The performance of the tandems can be traced back to the quality of the individual fibres.
Extensive X-ray testing has been done on all constituents, from several fibres up to tandem level, using
pencil beam and, for the first time, full beam illumination at PANTER. The results of these campaigns
and of reflectometry measurements are discussed in this paper and have been used throughout the
technology development program to monitor the X-ray performance. It will be shown that the quality
of focussing micro-pore X-ray optics is now high enough to achieve an angular resolution of several
arc minutes and that the multi-fibres are as good as 20 arc seconds, demonstrating the potential of this
technology. The tandems can be combined and assembled into larger geometries, hence forming a very
light and compact X-ray lens of ~200 mm diameter and a focal length of 1 m. This is part of an ESA
breadboard program discussed elsewhere in this conference.