Patent ID: 11966012
Assignee: CORETRONIC CORPORATION
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. A projection lens configured to project an image beam provided by a light valve onto a screen, wherein the projection lens have only four lenses which are a first lens, a second lens, a third lens, and a fourth lens, the projection lens comprises a first lens group and a second lens group in order from a screen side to a display side along an optical axis, the first lens group consists of the first lens and the second lens, the second lens group consists of the third lens and the fourth lens in order from the screen side to the display side along the optical axis, and the first lens, the second lens, the third lens, and the fourth lens are glass lenses, wherein each of the first lens to the fourth lens has a screen side surface facing the screen side and allowing the image beam to pass, and a display side surface facing the display side and allowing the image beam to pass, wherein:
the first lens has a negative refractive power, the second lens has a positive refractive power, the third lens has a negative refractive power, and the fourth lens has a positive refractive power; and
the projection lens satisfies:

2<TTL/f<5,

wherein TTL is a distance from the screen side surface of the first lens to the display side surface of the fourth lens on the optical axis, and f is an effective focal length of the projection lens, and

BFL/f>1.45,

wherein BFL is a distance from the display side surface of the fourth lens to a display surface of the light valve on the optical axis.