The result of a design study on a Focal Plane Instrument for the 6.5 to 175 nm wavelength range is described. The instrument is meant to be used in combination with a grazing incidence telescope consisting of a sector out of a full revolution configuration mirror system, type Wolter II. The presented design is based on the principles of grazing incidence reflection and conical diffraction. The absolute efficiency of a grating in a conical mount is high. The combination of a plane grating with some mirrors for imaging therefore results in an arrangement with a satisfactory instrumental transmission. The outcome of efficiency calculations is presented. The spectral image can be made stigmatic over the entire wavelength range in a field of view with sufficiently large dimensions. Simultaneously, radiation from 240 spatial pixels of 1 arcsec x 1 arcsec is analyzed in four wavelength bands.With a change of the angle of incidence on the grating it is possible to choose these bands, with some restrictions, anywhere in the mentioned wavelength range. The spectral resolution varies from 0.003 nm to 0.0075 nm. For detection micro-channel arrays are chosen.