Projection television device and screen

A lens system comprising:

• a first fold mirror and a second fold mirror, the second fold mirror being disposed on an enlargement side of the first fold mirror;
• a first positive lens disposed on a reduction side of the first fold mirror;
• a second positive lens disposed on an enlargement side of the second fold mirror;
• and
• at least three negative lenses disposed on the enlargement side of the second fold mirror, wherein:
• an image path includes a first part directed through the first positive lens, a second part between the first fold mirror and the second fold mirror, and a third part directed through the second positive lens,
• the first part of the image path is substantially orthogonal to the second part of the image path,
• the third part of the image path is substantially orthogonal to the second part of the image path,
• the first part of the image path is substantially parallel to the third part of the image path,
• a light direction in the first part is opposite to a light direction in the third part,
• the second positive lens is disposed between the second fold mirror and the three negative lenses,
• the three negative lenses include a first negative lens,
• the first negative lens is disposed on a most enlargement side of the lens system, and
• a diameter of the first negative lens is larger than a length of the second fold mirror.