Ronchi test for refractive optics off-axis using a nodal bench

Abstract

When evaluate the quality of the optical systems using the Ronchi test [1], the source and Ronchi ruling should be placed on the axis systems. In order to know the quality of the system in off-axis, we propose use the nodal optical bench. In particularly we use the principal property of this instrument, its consists when we mounted the refractive system in a rotating mount and his mechanical axis coincide with nodal point, we can rotated about the nodal point then the focal point of systems does not have any movement in a focal plane. So, now we can put a Ronchi ruling in the exit pupil and observe the pattern of fringes, without movement of the source and the ruling. For this, we placed the CCD camera in the focal plane of the refractive system and focused in the exit pupil; the principal advantage of this proposal is test the system without auxiliary optics. For implemented this options we use a simple optical system, one positive singlet lens. In particularly the lens are rotated 4, 12, 16, 20, 24, 28 and 32 degrees. In the optical setup we use a Ronchi ruling of 20 lines/inch, 50 lines/inch and 200 lines/inch in each case.