| 摘要 |
A transmissive overhead projector (10) includes a Fresnel lens assembly (26) which has an f-number of about 0.25 and is capable of dioptrically focusing light at an incident angle of at least 60 DEG with respect to a perpendicular to the Fresnel lens assembly (26). This refractive power of the Fresnel lens assembly (26) allows the overhead projector light source (22) to be positioned very close to the Fresnel lens assembly (26) and consequently allows a significant reduction in the base height of the overhead projector (10). |
