Quality Claims, Wave Ratings and Testing of Mirrors

Why are optical tolerances important for telescope mirrors? No manufacturing operation performed by human beings has tolerances as demanding as telescope optics. The quality of a telescope mirror's performance depends on care in its production, including the application of a meaningful tolerance for spherical aberration. By "meaningful" we mean that the tolerances used by the optician must have a direct correspondence to the expected level of performance in the telescope. The process tolerance should be designed to produce the smallest possible star image, in addition to minimizing microfinish and large-scale roughness. This will assure that roughness or edge problems will not create scattered light and loss of contrast at the wavefront.

Working Tolerance. Our working tolerance is 1/10 wave (wavefront) peak-to-valley and 1/36 wave RMS (Strehl Ratio = .97). The software which we use displays identical results to wavefront calculations per Texereau, and program output compares closely to commercial programs designed to calculate wavefront error. Our optics have no more than 1/10 wave indicated error at the wavefront. You will receive a signed Statement of Quality for your serialized mirror that attests to the attainment of these stated tolerances. We maintain records of inspection and test on-site.

Wave Ratings. Our working tolerance is 1/10 wave (wavefront) peak-to-valley and 1/36 wave RMS (Strehl Ratio = .97). The software which we use displays identical results to wavefront calculations per Texereau, and program output compares closely to commercial programs designed to calculate wavefront error. Our optics have no more than 1/10 wave indicated error at the wavefront. You will receive a signed Statement of Quality for your serialized mirror that attests to the attainment of these stated tolerances. We maintain records of inspection and test on-site.

Testing and Test Data. The only meaningful purpose of testing is to determine and apply needed corrections, based on mirror surface conditions revealed by testing, during the figuring process. Test output data must contain sufficient information to confirm achievement of target values and tolerances. Testing is a tool for building in quality, but cannot "add it on" after the fact. We quantitatively test the mirror at each step until figuring is completed. Your mirror will be made as good as it can be made, and will not be released for shipment until it meets the established numeric criteria for wavefront accuracy, as well as smoothness and edge criteria. The data reduction is identical to that described by Texereau in How to Make a Telescope, 2d Edition.