At both ends of the lens stack should be installed a pinhole (2D lenses) or a slit (1D lenses) in order to **limit the incoming beam** in its lateral extension and to **reduce scattered radiation** (Figure 1). The geometric aperture of the pinholes and the slits should be slightly smaller than the geometric aperture of the lenses. We offer suitable **high-precision** pinholes and slits for all lens types.

In Figure 2, the following notation is used: F thickness of the pinhole/slit, 2R_{0} width of the pinhole/slit, L length of the slit. A typical value for the thickness F is 1.0 mm for the pinholes and 2.0 mm for the slits. The length L of the slits usually is 2.0 mm.

Note that the slits consist of two components, allowing for an exactly rectangular cross section without rounded corners (Figure 2 right).