Very efficient mirrors designed for rejection of the 30.4 nm HeII line while transmitting the 28.4 nm FeXV line are needed for observations of the solar corona. Light traps, based on multilayered structures, using moderately absorbing diffractor layers of SiO2 and aluminum as spacer material, have been successfully fabricated providing dramatically high rejection ratios. However, accurate tuning at the desired wavelength has proven to be extremely difficult to achieve in combination with high nominal reflectivity. Very slight deviations of thicknesses or optical constants can easily destroy the desired antiresonance effect. Classical Mo/Si structures, although somewhat less selective, can also be specially designed for this application and they prove more amenable to proper adjustment.