Savvy about Standards

At Savvy Optics, we specialize in American National and International Standards for optics. With experts participating in most optics standard development efforts at ANSI/OEOSC and ISO, we are always in-the-know about which standard is most applicable for each situation and optics requirements, and can give you savvy advice about how to change your specifications, drawings, or inspection methods. Drop us a line for more information about how Savvy Optics can help you. Here are a couple of common examples:

ISO 10110 Drawing Standard

Published in 1996, the International standard for optics drawings continues to gain popularity throughout the world. Based loosely on the German DIN 3140 standard for optics drawings, it is a pictographic/symbolic notation system intended to reduce the language ambiguity associated with translation of notes. Nevertheless, it can be quite counter-intuitive for engineers and opticians trained in the United States, where most drawings are notes-based, structured loosely on MIL-STD-34 optical drawings notation.

Training and education in the area of this standard is one of Savvy Optics' specialties. With members on all of the critical working groups for fundamental standards in the US and Internationally, Savvy Optics always has access to the latest standards and their interpretations. Currently, Savvy Optics offers the only ISO 10110 on-site training program that is accredited by OEOSC, the Optics and Electro-Optics Standards Council.

The latest news is that, effecting 2020, the US will adopt WITHOUT MODIFICATION the ISO 10110 drawing standard. This new adoption marks a key turning point in the use of ISO 10110 as an international standard. The new series of American National Standards shall be called ANSI/OEOSC ISO 10110, and will be identical to the international version.

Surface Imperfections

Since 1945, MIL-PRF-13830B, in one or another of its various forms, has been used as the standard for surface imperfections specification and measurement throughout the world. Increasingly, though, demanding applications and exacting customers have been making this standard obsolete. Now the optics industry has a choice of which standard to use, and it's not always clear which is the best path.

In addition to the MIL standards, there is now ANSI/OEOSC OP1.002-2009, the newest offering for surface imperfections, based on the original MIL specifications. Savvy recommends this for anyone who needs a cosmetic specification for new optics, with a minimum of conversion cost from the MIL methods. Using the same notation and comparison standards as the MIL, it offers the simplest path forward, for people who can accept the "relative brightness" metric.

A third alternative is ISO 10110-7. This method, based mostly on the German DIN 3140 standard, is becoming increasingly popular in Europe and around the world. While the scratch standard is based on line width, the standard does allow for visual comparison, using chrome-on-glass comparison standards. Since chrome on glass has a very different "relative brightness" from "real" scratches on an optic, microscopes are often required to validate the smaller scratch widths. Savvy recommends ISO 10110-7 for applications where actual scratch width, rather than brightness, is what matters in the application.

2017 saw the publication of a new version of ISO 10110-7 and it's sister metrology standard, ISO 14997. The new version of the ISO surface imperfection standard includes a visibility notation based on the MIL standard. The new version is streamlined and simplified but sticks to the basis approach of a visual inspection of parts and a comparison standard for gauging scratches and digs. Accumulation and concentration rules are basically the same as for the MIL and ANSI standards.

Mid-Spatial Frequency Ripple (Waviness)

With the world-wide conversion to deterministic polishing methods for the manufacture of precision aspheres and even spherical optics, an entirely new type of form error has emerged from the relative obscurity of X-ray optics and high-powered lasers and into the mainstream. Modern deterministic polishing methods such as MRF or STP will leave a signature "ripple" in the surface form related to the tool size, the step size, and other polishing parameters.

Mid-spatial frequency (MSF) errors, also called "ripple" or "waviness," are typically defined as surface form errors that are beyond the practical reach of Zernike specifications (say 5 or 6 cycles per diameter) but still too long a scale length to be practically evaluated using roughness measurement instruments (e.g. an AFM). On a typical 50 mm diameter optic, this would be the 5 mm to 0.1 mm spatial periods.

There is no practical standard for mid-spatial frequency ripple on optics per se. There are some good standards in the automotive industry, and there is an excellent notation standard, ISO 10110-8, which allows the use of RMS surface texture over discrete wavebands and use of the best analytic tool for MSF ripple, the power spectral density of the surface profile or PSD. Since the PSD is a Fourier domain technique, many manufacturers cannot comfortably sign up to a PSD without some significant hand-holding. Judicious use of notes for RMS slope specifications or RMS surface errors versus spatial frequency bands are the most common methods to specify MSF ripple, but each has its weakness.

We have just completed rewriting the ISO 10110-8 drawing notation to add areal specifications for surface texture. Any comments or feedback on this topic will be greatly appreciated!