1. Technical Field
The present invention relates to a projection lens unit employed in a rear projection device, a front projection apparatus or the like and a manufacturing method of the projection lens unit.
2. Related Art
A rear projection television (RPTV) having a projection unit which is placed on a rear side of a large screen and projects an image to the large screen (refer to, for example, JP-A-2003-114479) is known. Recently, thin-screen television having a large screen such as a plasma display television, a liquid crystal television have been spread, also RPTV which is more inexpensive than the plasma display television and the liquid crystal television still has a strong demand.
Although RPTV is provided with a projection unit on a rear side of the screen thereof, and therefore, RPTV needs some degree of thickness. But it has been proposed that RPTV employs a refractive optical system so as to be in a thinner shape (refer to, for example, JP-A-2000-187274 (corresponding to GB-A-2343966)). The refractive optical system employed by RPTV includes a convergent optical system that converges image light for refracting the image light, a mirror that reflects the converged image light, and a magnifying optical system that magnifies the converged image light after reflecting the converged light. The magnifying optical system includes plural lenses, the image light is magnified at each time of transmitting through each lens. In order to deal with magnified image light, according to the lens constituting the magnifying optical system, the nearer lens is arranged to the screen side, the larger the diameter of lens is.
However, according to the magnifying optical system, as shown by FIG. 3, there poses a problem that ghost is generated by image light reflected without transmitting through a first lens 101 being further reflected by a lens holding frame 103 holding a second lens 102 which is next to the first lens 101.
The invention resolves the problem and an object of the invention is to provide a projection lens unit for preventing ghost from being generated caused by a lens holding frame that holds a lens constituting a magnifying optical system, and a manufacturing method of the projection lens.