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Telescopic zoom lens systemTelescopic zoom lens system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070188888, Telescopic zoom lens system. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]1. Field of the Invention [0002]The present invention relates to a telescopic zoom lens system suitable for a single-lens reflex (SLR) camera. [0003]2. Description of the Prior Art [0004]In conventional telescopic zoom lens systems, a four-lens-group zoom lens system including a lens group having a positive refractive power (hereinafter, a positive lens group), a lens group having a negative refractive power (hereinafter, a negative lens group), a positive lens group and a positive lens group, in this order from the object, has been widely used, as disclosed in, e.g., Japanese Unexamined Patent Publication (JUPP) No. 2000-019398, JUPP No. 2002-006215, JUPP No. 2003-090958, JUPP No. 2003-202497, JUPP No. 2003-344766 and JUPP No. 2004-109559. [0005]The above-discussed conventional telescopic zoom lens systems have been designed for a SLR camera with the 135 (35 mm) film format users already owning a lot of exchangeable photographing lenses- for the 135 (35 mm) film format strongly wish to use a conventional exchangeable photographing lens with a recent digital SLR camera. Here, it should be understood that such a compatibility can be attained only when a digital SLR camera is provided with the same flange back length as that of a conventional SLR camera. [0006]However, the size of an imaging device (CCD) of a digital SLR camera is considerably smaller than the frame size of the 135 (35 mm) film format. If an exchangeable photographing lens for the 135 (35 mm) film format is simply mounted on a digital SLR camera, the angle-of-view for photographing becomes smaller. [0007]If an attempt is made, in a digital SLR camera, to maintain the same angle-of-view that can be attained in a conventional SLR camera, there is a need to shorten the focal length of an exchangeable photographing lens by the dimensional-ratio of frame size of the 135 (35 mm) film format to the size of an imaging device (CCD). [0008]On the other hand, as discussed above, for the purpose of attaining the compatibility in which a conventional exchangeable photographing lens can be used with a digital SLR camera, the flange back length of a digital SLR camera has to be made the same as that of a conventional SLR camera. Accordingly, in the case when an exchangeable photographing lens for a digital SLR camera is newly designed, there exists a problem to be solved, i.e., both a shorter focal length and a longer back focal distance have to be attained at the same time. Here, note that just redesigning conventional photographing lenses for adjusting the same with the size of an imaging device (CCD) cannot solve the above problem, because according to such a simple re-scaling, when the focal length becomes shorter, the back focal distance also becomes shorter. [0009]The present invention is to provide a miniaturized telescopic zoom lens system having the following features: [0010](i) an angle-of-view of approximately 10.degree. to 30.degree. (the zoom ratio: a little less than 3); [0011](ii) a long back focal distance; [0012](iii) a short focal length; [0013](iv) high optical quality; and [0014](v) high operability. SUMMARY OF THE INVENTION [0015]According to an aspect of the present invention, there is provided a telescopic zoom lens system including a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group, in this order from the object. [0016]Upon zooming from the short focal length extremity to the long focal length extremity, the positive first and the positive fourth lens group remain stationary, the negative second lens group moves toward the image, and the positive third lens group first moves toward the image and thereafter moves toward the object. [0017]The positive first lens group is constituted by a positive front sub-lens group and a positive rear sub-lens group which are separated at a maximum air-distance therebetween. [0018]The positive rear sub-lens group functions as a focusing lens group, and is constituted by a negative meniscus lens element having the convex; surface facing toward the object, and a positive lens element having a convex surface facing toward the object, in this order from the object. [0019]The positive rear sub-lens group satisfies the following condition: 2.7<f1R/ft<3.5 (1) [0020]wherein [0021]f1R designates the focal length of the positive rear sub-lens group; and [0022]ft designates the focal length of the entire telescopic zoom lens system at the long focal length extremity [0023]It is preferable that the positive fourth lens group include a front sub-lens group and a rear sub-lens group separated at a maximum air-distance therebetween, and that the rear sub-lens group satisfy the following condition: 1.8<f4R/fw<3.6 (2) [0024]wherein [0025]f4R designates the focal length of the rear sub-lens group of the positive fourth lens group; and Continue reading about Telescopic zoom lens system... Full patent description for Telescopic zoom lens system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Telescopic zoom lens system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Telescopic zoom lens system or other areas of interest. ### Previous Patent Application: Zoom lens system and image-pickup apparatus Next Patent Application: Auto-focusing camera module and auto-focusing lens module Industry Class: Optical: systems and elements ### FreshPatents.com Support Thank you for viewing the Telescopic zoom lens system patent info. 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