Patent ID: 8976457
Filing Date: 2015-03-10
Classification: G02B

Abstract:
1. A projection lens system of a five- or six-group design which achieves zooming by varying distances between groups, wherein a most enlargement-side group has a negative optical power, and a most reduction-side group has a positive optical power, when a group having a largest movement amount during zooming is referred to as an α-th group and a group located next to the α-th group and having a second largest movement amount during zooming is referred to as a β-th group, a composite optical power of the α-th and β-th groups is constantly positive, when the α-th and β-th groups are together considered a single component referred to as an (α+β) component, a group next to the (α+β) component on an enlargement side thereof is referred to as a γ-th group, and a group next to the (α+β) component on a reduction side thereof is referred to as a δ-th group, at least one of the γ-th and δ-th groups moves during zooming, and an aperture stop is arranged on the reduction side of the (α+β) component, during zooming from a telephoto end to a wide-angle end through a predetermined middle position that fulfills conditional formula (0) below, while the most enlargement-side and most reduction-side groups remain stationary, the α-th and β-th groups move from the enlargement side to the reduction side, and conditional formulae (X1A), (X1B), (X2A), (X2B), (X3A), and (X3B) below are fulfilled: where ft represents a focal length of the entire system at the telephoto end; fm represents a focal length of the entire system at the middle position; fw represents a focal length of the entire system at the wide-angle end; ΔTMα represents a movement amount of the α-th group from the telephoto end to the middle position; ΔTMβ represents a movement amount of the β-th group from the telephoto end to the middle position; ΔTMγδ represents the larger of movement amounts of the γ-th and δ-th groups from the telephoto end to the middle position; ΔTWα represents a movement amount of the α-th group from the telephoto end to the wide-angle end; ΔTWβ represents a movement amount of the β-th group from the telephoto end to the wide-angle end; and ΔTWγδ represents the larger of movement amounts of the γ-th and δ-th groups from the telephoto end to the wide-angle end.