Here are a few double-pass interferograms of various optical equipment items located at our facility. Note that the actual surface figure error is half of what is evident in these interferograms, due to double-pass operation of the SPPDI™.
Interferogram of 4.25″ diameter f/4.16 concave spherical mirror measured at the f/8.32 center of curvature. This mirror is used at Kerry Optical Systems, LLC as a reference mirror, with surface figure certified by the Zygo Corporation. This mirror is used as a master reference tool for validating and certifying the performance of each SPPDI unit prior to sale. Each SPPDI unit must yield a set of interferograms of this master reference mirror that match the Zygo results to within +/-.01 waves of astigmatism and +/-.01 waves of spherical aberration before the unit is considered acceptable for sale.
We are indebted to Mr. Dale Eason for his excellent DFTFringe interferometric fringe analysis software.
2-inch diamete
r f/4 aluminized concave mirror measured at the f/8 center of curvature. Astigmatism is noted, as well as a “turned edge.” A central divot is possibly due to mechanical “print-through” from the polishing spindle during manufacture.
Commercial 50mm aperture (f/15?) “department store quality” achromatic refractor objective. Surprisingly, this objective exhibits diffraction-limited performance at 650nm.
Interferogram of a commercial 70mm aperture f/6.8 two-element apochromatic refractor objective measured in a double-pass setup against an optical flat. Some residual aberration is evident.
Interferogram of a commercial 127mm aperture three-element apochromatic refractor objective measured in a double-pass setup against an optical flat. Some residual aberration is evident in the outer periphery of this lens.
Interferogram of a 6-inch aperture f/5 two-element air-spaced achromatic lens measured in a double-pass setup against an optical flat. This is the objective lens of a moderately low cost telescope sold by a well known telescope manufacturer.
