An optical train is designed and built to take a Ø1 inch collimated output sample beam from a 10.6 μm wavelength Wyko IR3 interferometer, and by use of a fast aperture-ratio lens, allow the diverging rays to pass through a steeply curved optical test dome, encounter a concave mirror and return to the interferometer for wavefront analysis. The advantage over off-the-shelf hardware is an ability to capture at one instant a large area or even the entire clear aperture, of a dome. The key to the design is the fast, f/0.65, highly-aspheric, diamond-turned, ZnSe lens, and the equally fast, very thick, deeply concave mirror. Other components allow for placement and rotation of the optical dome under test. Operation at 10.6 μm allows loose fabrication tolerances for the surfaces in the visible wavelengths, yet the system is of reference quality in the infrared. The subsystem is modular so that it may be easily removed to gain access to the standard output port of the interferometer for other purposes.