Viewing system including a holographic optical device allowing images to be displayed in different planes

Viewing systems are provided which include a screen and an optical collimation device including two holographic optical elements working by reflection, the first holographic optical element being closer to the screen, the second holographic optical element being closer to an observer. In the system, the screen displays a first object at a first wavelength and a second object at a second wavelength. Each holographic optical element includes two holographic treatments, each treatment being able to reflect one of the two wavelengths and to transmit the other wavelength. The first holographic element and the second holographic element are arranged such that the image of the first object forms at a first distance from the screen and that the image of the second object forms at a second distance from the screen, different from the first distance.