Immersion microscope objective and laser scanning microscope system using same
View Patent ↗An immersion microscope objective formed of thirteen or fewer lens elements includes, in order from the object side, first and second lens groups of positive refractive power, a third lens group, a fourth lens group having negative refractive power with its image-side surface being concave, and a fifth lens group having positive refractive power with its object-side surface being concave. The first lens group includes, in order from the object side, a lens component that consists of a lens element of positive refractive power (when computed as being in air) and a meniscus lens element having its concave surface on the object side. Various conditions are satisfied to ensure that images of fluorescence, obtained when the immersion microscope objective is used in a laser scanning microscope that employs multiphoton excitation to observe a specimen, are bright and of high resolution. Various laser scanning microscopes are also disclosed.
1. An immersion microscope objective that has, in order from an object side, a first lens group, a second lens group, a third lens group, a fourth lens group and a fifth lens group, wherein:
the first lens group includes
a cemented lens consisting of a positive lens on the side nearest an object and a meniscus lens having its concave surface on the object side, and
a single lens;
the second lens group has positive refractive power; and
the following conditions are satisfied:
0.15 >n 1 −nw> 0.05
4 >|rb/dt 3|>0.9
fs/f< 1.99
where
n 1 is the refractive index of a positive lens nearest the object side in the first lens group,
nw is the refractive index of a medium that fills a space between the first lens group and the object,
rb is the radius of curvature of a cemented surface of the cemented lens,
dt 3 is a distance along an optical axis, in mm, between an object surface and the cemented surface,
fs is the focal length of the cemented lens, and
f is the focal length of the immersion microscope objective.
2. The immersion microscope objective according to claim 1 , wherein the following condition is satisfied:
dt 5 −dt 4>2.8 mm
where
dt 4 is a thickness in mm of a positive lens nearest the object side in the first lens group, and
dt 5 is a thickness in mm of the meniscus lens in the first lens group.
3. The immersion microscope objective according to claim 1 , wherein: the second lens group is a biconvex lens.