US 12,222,480 B2
Projection zoom lens and projection device
Akitoshi Usui, Kanagawa (JP)
Assigned to RICOH INDUSTRIAL SOLUTIONS INC., Kanagawa (JP)
Filed by Akitoshi Usui, Kanagawa (JP)
Filed on Nov. 30, 2021, as Appl. No. 17/456,918.
Claims priority of application No. 2020-167232 (JP), filed on Oct. 1, 2020.
Prior Publication US 2022/0107484 A1, Apr. 7, 2022
Int. Cl. G02B 15/14 (2006.01); G02B 13/04 (2006.01); G02B 13/16 (2006.01); G02B 15/177 (2006.01); G02B 15/20 (2006.01)
CPC G02B 15/177 (2013.01) [G02B 13/04 (2013.01); G02B 13/16 (2013.01); G02B 15/20 (2013.01)] 12 Claims
OG exemplary drawing
 
1. A projection zoom lens is configured by a first group having a negative refractive force, a second group having a positive refractive force, a third group having a positive refractive force, an aperture diaphragm, a fourth group having a positive refractive force, and a fifth group having a positive refractive force,
wherein the groups are arranged in aforementioned order from an enlarged-side to a reduced-side in the projection zoom lens,
wherein the projection zoom lens is telecentric on the reduced-side,
wherein the first group is configured by
a first sub-lens group having a positive or a negative refractive force,
a second sub-lens group having a negative refractive force, and
a third sub-lens group having a negative refractive force,
wherein the sub-lens groups are arranged sequentially from the enlarged-side to form a focusing group,
wherein the second group to the fifth group constitute a zooming group,
wherein the focusing group changes a spacing between the first sub-lens group and the second sub-lens group and a spacing between the second sub-lens group and the third sub-lens group, while the projection zoom lens is changing focus from an infinite distance to a near distance, and
wherein each of the second group to the fourth group is moved independently to the enlarged-side while the projection zoom lens is magnifying from a wide-angle end to a telephoto end, thereby performing zooming,
wherein a focal length of the focusing group is fg1, a focal length of the second group of the zooming group is fg2, and a focal length of an entirety of the projection zoom lens at the wide-angle end is fw, the following conditional formulae are satisfied:
−2.5<fg1/fw<−1.5  (8)
5<fg2/fw<12  (9).