Imaging tube having a reflective photocathode and internal optical means

An imaging tube for imaging light energy comprising

• a housing,
• a first window,
• a second window,
• a reflective photocathode emitting electrons in response to light energy,
• a conversion element for converting electrons to light energy, and
• an optical element,
• said first window and said second window being mounted in said housing to define therewith a vacuum-tight zone and to transmit therethrough respectively a first set and a second set of rays of light energy, said first set being said light energy to be imaged,
• said first window being arranged to transmit said first set along a first axis,
• said second window being arranged to transmit said second set along a second axis,
• said first axis intersecting said second axis at an angle of less than 180.degree.,
• said conversion element being mounted to receive said electrons and to provide said second set,
• said optical element being mounted in said housing and including a centrally discontinuous portion,
• said optical element being oriented with respect to said first window and said photocathode so that said first set is directed by said optical element onto said photocathode, and at least one of said electrons and said second set is directed through said centrally discontinuous portion.