Optical surface specifications that prescribe the allowable error as a function of spatial frequency, such as limits on the PSD or local slope, are becoming more common. It is often important to characterize errors on an optical surface that range in size from the wavelength of light all the way up to the size of the optic. A range of instruments is required to accurately measure surface errors over this full spectrum and a typical optics shop has gaps in coverage. High-resolution subaperture stitching is one way to extend an instrument's spatial frequency measurement capability and close a problematic gap in this coverage. An explanation of how stitching increases resolution will be discussed and examples will be given that show the benefits of stitching over full-aperture metrology.
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