Viewer

An optical device for viewing an inner layer of material which is at least semitransparent and which is surrounded on two sides by outer layers of material which is also at least semitransparent, said device comprising:

• illuminating means for illuminating a plurality of spaced-apart narrow areas of said inner layer, said illuminating means including
• a first collimating plate arranged to pass light travelling in a direction generally perpendicular to said layers of material and
• a first array of lenses positioned between said first collimating plate and one of said outer layers, each lens of said first array being
• elongated in a direction generally parallel to said layers of material and
• shaped to focus collimated light emerging from said first plate onto one said narrow area of said inner layer, said narrow area extending generally parallel to the direction of elongation of said lens, and
• viewing means for viewing light transmitted through said plurality of narrow areas, said viewing means including
• a second collimating plate and
• a second array of lenses positioned between said second collimating plate and the other of said outer layers, each lens of said second array being
• elongated in a direction parallel to the elongation direction of said first array and
• shaped to bend only light transmitted through one said narrow area into the direction of collimation of said second plate, whereby only light from said narrow area is transmitted through said second plate, and
• means for forming images of said narrow areas from the light transmitted through said second plate.