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I’ve been using this flat to check some lenses I’m polishing, and the low thermal expansion of the fused quartz is a huge plus for consistent results. The surface is remarkably smooth—no visible scratches or haze right out of the box.

The fused quartz construction gives me real peace of mind during long measurement sessions, since thermal drift is barely a factor. These flats are dead flat as far as my interferometer can tell, which is exactly what I needed as a reference for calibrating my other optics.

I've been checking surface figure on some vintage lenses and this flat gives me clean, readable fringes every time. The fused quartz barely moves with temperature swings in my shop, which matters when I'm chasing a quarter-wave.