Abstract: A relay optical system includes, in order from, an object side, a first cemented lens, a second cemented lens having a positive refractive power, a third cemented lens which is plane-symmetric to the second cemented lens, and a fourth cemented lens which is plane-symmetric to the first cemented lens, the first cemented lens includes a first lens having a positive refractive power and a second lens having a negative refractive power, the second cemented lens includes a third lens and a fourth lens, a shape of the first lens is a biconvex shape, a shape of the second lens is a biconcave shape, and the following conditional expression (1), in which f2 denotes a focal length of the second lens and fCL12 denotes a combined focal length of the first cemented lens and the second cemented lens, is satisfied: ?0.4<f2/fCL12<?0.1??(1).

Abstract: Optical objective dimensioned to operate as part of intravascular endoscope probe and including first and second groups of lens elements. The first group of lens elements includes a first meniscus lens with a negative dioptric power and a first optical doublet. The second group of lens elements include a sequence of second, third, and fourth optical doublets and a second meniscus lens with a positive dioptric power. At least one of the first and second groups of lens elements includes an aspheric refractive surface, thereby reducing distortion down to under 1% for field angles up to at least 40 degrees. Methods for using same, including embodiments with such multiple optical objectives used for acquisition of images of targets with fixed FOV and image fusion, providing enhanced imaging data for target analysis.

Abstract: Low-power objective lenses for a microscope are disclosed. The objective lenses exhibit apochromatic optical performance at a numerical aperture of at least 0.1 and have a magnification of about 2.times. or less. Each such objective lens comprises, in order from the object side, a first lens group having positive refractive power; a second lens group having negative refractive power and comprising a negative meniscus lens with a concave surface oriented toward the image side; a third lens group having negative refractive power and having at least one cemented surface; and a fourth lens group having positive refractive power and comprising a positive meniscus lens element with a convex surface oriented toward the image side, and a positive cemented lens including a negative lens element cemented to a positive lens element. The objective lenses satisfy the condition: 1.2<f.sub.1 /D.sub.1 <2.3 and other conditions, wherein f.sub.l is focal length of the first lens group and D.sub.