A method for measuring a property of a test object with an interferometer , the method comprising: a. providing calibration information relating a focus setting for the interferometer to a position of the test object relative to a reference surface of the interferometer , wherein the focus setting is a position of best-focus for an image of the test object produced by the interferometer; b. determining the position of the test object relative to the reference surface; and c. using the interferometer to collect interferometric images of the test object for use in measuring the property of the test object ; d. wherein the method further comprises at least one of the following: i. prior to collecting at least some of the interferometric images, adjusting a focus of the interferometer in hardware based on the calibration information and the determined position of the test object relative to the reference surface to improve a degree of focus of the interferometric images; and ii. using one or more electronic processors to mathematically propagate at least one wavefront derived from the interferometric images based on the calibration information and the determined position of the test object relative to the reference surface to improve a degree of focus of the wavefront derived from the interferometric images, wherein the interferometer comprises a light source having a variable wavelength, wherein the interferometric images are collected while adjusting the wavelength of the light source, and wherein the position of the test object relative to the reference surface is determined based on the interferometric images collected while adjusting the wavelength of the light source. a. providing calibration information relating a focus setting for the interferometer to a position of the test object relative to a reference surface of the interferometer , wherein the focus setting is a position of best-focus for an image of the test object produced by the interferometer; b. determining the position of the test object relative to the reference surface; and c. using the interferometer to collect interferometric images of the test object for use in measuring the property of the test object ; d. wherein the method further comprises at least one of the following: i. prior to collecting at least some of the interferometric images, adjusting a focus of the interferometer in hardware based on the calibration information and the determined position of the test object relative to the reference surface to improve a degree of focus of the interferometric images; and ii. using one or more electronic processors to mathematically propagate at least one wavefront derived from the interferometric images based on the calibration information and the determined position of the test object relative to the reference surface to improve a degree of focus of the wavefront derived from the interferometric images, i. prior to collecting at least some of the interferometric images, adjusting a focus of the interferometer in hardware based on the calibration information and the determined position of the test object relative to the reference surface to improve a degree of focus of the interferometric images; and ii. using one or more electronic processors to mathematically propagate at least one wavefront derived from the interferometric images based on the calibration information and the determined position of the test object relative to the reference surface to improve a degree of focus of the wavefront derived from the interferometric images, <EOS>