An optical configuration suited to the monitoring of a process flow through the wall of a containment vessel for producing a high-quality, high-NA sample focus and reduced residual positive spherical aberration. The invention includes an optical path with a window extending through, and sealed to, the wall of the containment vessel, and an optical surface disposed in the optical path associated with minimizing aberration, increasing numerical aperture, or both. The window has a surface facing into the process flow and a surface facing away from the process flow and, the surface facing away from the process flow is associated with minimizing aberration or increasing numerical aperture. A lens is disposed outside the containment vessel and in the optical path, with the surface of the window facing the lens being substantially spherical. With such an arrangement, the light rays of the optical path are generally normal to the surface of the window facing the lens.