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.
This mirror was made by Carl Zambuto (see https://zambutomirrors.com/). We purchased this mirror from Carl and sent it to Zygo for certification. It is indeed as good as it appears on the interferogram.
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.
