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We report in this paper the test of a plane holographic optical element to be used as an aberration-corrected grating for a slitless spectrograph, inserted in a convergent telescope beam. Our long term objective is the optimisation of a specific hologram to switch the auxiliary telescope imager of the Vera Rubin Observatory into an accurate slitless spectrograph, dedicated to the atmospheric transmission measurement. We present and discuss here the promising results of tests performed with prototype holograms at the CTIO $0.9\,$m telescope during a run of 17 nights in May-June 2017. After their on-sky geometrical characterisation, the performances of the holograms as aberration-balanced dispersive optical elements have been established by analysing spectra obtained from spectrophotometric standard stars and narrow-band emitter planetary nebulae. Thanks to their additional optical function, our holographic disperser prototypes allow to produce significantly better focused spectra within the full visible wavelength domain $[370,1050]\,$nm than a regular grating, which suffers from strong defocusing and aberrations when used in similar conditions. We show that the resolution of our slitless on-axis spectrograph equipped with the hologram approaches its theoretical performance. While estimating the benefits of an hologram for the spectrum resolution, the roadmap to produce a competitive holographic element for the Vera Rubin Observatory auxiliary telescope has been established., 17 pages, 27 figures, 4 appendices, accepted for publication in MNRAS

A holographic camera that makes it possible to take pictures outside the holography laboratory has been developed and fabricated to record color holograms of museum pieces, using Denisyuk's method. The camera, with dimensions 30×40×50cm and mass 12kg, is a white-light laser projector capable of recording color holograms up to 30×40cm in size on Ultimate photographic plates fabricated in the laboratory. The camera requires no massive vibration-proof table, water cooling, or excessive electric power, and this is an important condition for operating it directly in museums or at the site where the objects to be pictured are found.