  We have designed, built, and characterized a high-resolution objective lens
that is compatible with an ultra-high vacuum environment. The lens system
exploits the principle of the Weierstrass-sphere solid immersion lens to reach
a numerical aperture (NA) of 0.92. Tailored to the requirements of optical
lattice experiments, the objective lens features a relatively long working
distance of 150 micrometers. Our two-lens design is remarkably insensitive to
mechanical tolerances in spite of the large NA. Additionally, we demonstrate
the application of a tapered optical fiber tip, as used in scanning near-field
optical microscopy, to measure the point spread function of a high NA optical
system. From the point spread function, we infer the wavefront aberration for
the entire field of view of about 75 micrometers. Pushing the NA of an optical
system to its ultimate limit enables novel applications in quantum technologies
such as quantum control of atoms in optical microtraps with an unprecedented
spatial resolution and photon collection efficiency.
