Reference Flat 90% reflective

The 1/20 wave surface accuracy is immediately obvious in the fringe pattern—dead straight lines with zero distortion. Took me less than ten minutes to validate my interferometer setup, and the 90% reflectivity gives a crisp, high-contrast return. Exactly what I needed for calibration work.

Interferometry setup was a breeze with this 4-inch flat—the 90% reflectivity gave me clean fringes right out of the box. Measured surface error came in right at the 1/20 wave spec, which is exactly what my calibration needed.

The surface accuracy on this one checked out at 1/20 wave on my interferometer, which is exactly what I needed for a collimation setup. It's held up well over a few weeks of handling, and the 4-inch size sits nicely on my bench without taking over.