Reading Optical Flats Part 1

I’m new to optical flat inspection, so bear with me as I walk through some of the things I’m trying to learn. This first of a series of videos presents the basics . . . possibly in excruciating detail . . . but, hopefully, a few points worth presenting to establish a firm basis for things to follow. I started using optical flats to evaluate progress while generating small lapping plates using plate to plate lapping techniques. The goal was to evaluate flatness on the order of 1/4 wavelength . . . about 6 micro-inches; although, I’m also interested in evaluating old gage blocks and other old metrology equipment . . . a potential subject for some future videos. While other metrology equipment offers the potential for accurate measurements . . . certainly in the 40 micro-inch (about 1 micron) range and better . . . optical flats offer the potential for measurements down to a few micro-inches with simple equipment. While new optical flats can be quite expensive, some are available used and as new old stock at tolerable prices. Even used monolights can be expensive so we’ll discuss some shop made options in a later video. For those interested in amateur . . . or even more serious . . . metrology work, optical flat inspection is worth consideration.