Figure 2: Principle of Fizeau and Michelson configurations for a large
multi-element interferometer (A,B). A is equivalent to Michelson's periscopic
train, while zoom lenses Z on each beam of the telescope-like array B provide
adjustable conversion from Fizeau to Michelson geometries. The zoom lenses are
assumed to preserve the image focus while changing the image scale. They can be
adjusted from a neutral position, providing the unit image magnification
corresponding to the Fizeau geometry (C), towards increasingly demagnified
images providing Michelson's wider sub-pupils (D). The variable focal ratio in
the sub-images leaves the array's global focal ratio
1/ nearly
invariant, thus not affecting the scale of the fine interference structure.
When zooming however, the image's Airy envelope varies in size since it is the
diffraction pattern of the sub-apertures.