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Abstract. The two Wide Field Cameras (WFCs) currently flying on the Italian/Dutch X-ray satellite BeppoSAX, image the X-ray sky in the energy range of 1.8 − 28 keV. The field of view is 20• , the angular resolution is 5 arcmin and the energy resolution is 20% at 6 keV, while the source location accuracy will generally be better than one arcmin. All values are at Full Width Half Maximum. The design is based on the coded mask principle where mask and detector both have sizes of about 25.6×25.6 cm 2 . The detector is a Multi Wire Proportional Counter with a position resolution which is better than 0.5 mm for energies below 10 keV. The mask pattern is based on a so called triadic residue set with elements of 1 mm 2 of which 33% are transparent for X-rays. The limiting sensitivity of the WFCs is a few mCrab in 10 5 s. The design and performance of the instrument is described here along with some calibration results and the principle of the image reconstruction.The WFCs represent the latest generation of coded mask X-ray cameras. Their unrivalled field of view, combined with appropriate spatial and temporal resolution and modest energy resolution make the instruments very well suited to perform extensive studies of large areas of the sky and to study transient X-ray phenomena.

We describe the design and performance of the Medium Resolution Spectrometer (MRS) for the JWST-MIRI instrument. The MRS incorporates four coaxial spectral channels in a compact opto-mechanical layout that generates spectral images over fields of view up to 7.7 x 7.7 arcseconds in extent and at spectral resolving powers ranging from 1,300 to 3,700. Each channel includes an all-reflective integral field unit (IFU): an 'image slicer' that reformats the input field for presentation to a grating spectrometer. Two 1024 x 1024 focal plane arrays record the output spectral images with an instantaneous spectral coverage of approximately one third of the full wavelength range of each channel. The full 5 to 28.5 µm spectrum is then obtained by making three exposures using gratings and pass-band-determining filters that are selected using just two three-position mechanisms. The expected on-orbit optical performance is presented, based on testing of the MIRI Flight Model and including spectral and spatial coverage and resolution. The point spread function of the reconstructed images is shown to be diffraction limited and the optical transmission is shown to be consistent with the design expectations.

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