1. Advantages

• A Fresnel imager with a sheet of a given size has vision just as sharp as a traditional telescope with a mirror of the same size, though it collects about 10% of the light.^[1][2]
• The use of vacuum for the individual subapertures eliminates phase defects and spectral limitations, which would result from the use of a transparent or reflective material.^[1]
• It can observe in the ultraviolet and infrared, in addition to visible light.^[2]
• It achieves images of high contrast, enabling observation of a very faint object in the close vicinity of a bright one.^[2]
• Since it is constructed using foil instead of mirrors, it is expected to be more lightweight, and therefore less expensive to launch, than a traditional telescope.^[3]
• A 30-metre Fresnel imager would be powerful enough to see Earth-sized planets within 30 light years of Earth, and measure the planets' light spectrum to look for signs of life, such as atmospheric oxygen. The Fresnel imager could also measure the properties of very young galaxies in the distant universe and take detailed images of objects in the Solar System.^[3]

2. Development

The concept has been successfully tested in the visible, and awaits testing in the UV. An international interest group is being formed, with specialists of the different science cases. A proposal for a 2025-2030 mission has been submitted to ESA Cosmic Vision call.^[1][4] In 2008 Laurent Koechlin of the Observatoire Midi-Pyrénées in Toulouse, France, and his team planned to construct a small ground-based Fresnel imager telescope by attaching a 20-centimetre patterned sheet to a telescope mount.^[3]

Koechlin and his team completed the ground-based prototype in 2012. It uses a piece of copper foil 20 cm square with 696 concentric rings as the zone plate. Its focal length is 18 metres. They were able to resolve the moons of Mars from the parent planet with it.^[5]