ISO 10110 vs. MIL specs

Within today’s optics community, the debate continues on the comparison of surface imperfections using two very different methods: ISO10110 vs. Mil-13830A. As ISO 10110 becomes more prevalent, it approaches surface quality from the perspective of engineering or quality control. Unlike the Mil-specs or ANSI standards that are based on the types of damage that are commonly caused by optics manufacturing processes, ISO opts for specifications that are more repeatable and objective. For surface quality and several other test specifications, the ISO standards are extremely regimented, and there is no wiggle room for interpretation as to what is and is not a passing optic. The format is standardized per the table below, and information should exist in the same place on every drawing.

Comparing Scratch/Dig specifications across the Standards
While the scratch/dig MIL-Spec can sound intimidating, it really is rather simple. The scratch element represents the length of a scratch on an optic's surface while the dig refers to a pit or depression in the surface form. The measurements of scratch and dig come from the MIL-13830A standards established in 1954; however, a key limitation with MIL-13830A is that it cannot be used to specify defects that fall below the smallest comparison standards 10/5 scratch/dig. On the surface (pun intended) the MIL-spec uses a set standard of measurements with a quality inspector using a 40watt light bulb or 15W cool white fluorescent lamp reviewing the optic against a plain dark background. The inspector compares the brightness of scratch/digs when compared to a calibrated standard card as a reference. The MIL standard tends to have some variability based on the inspectors visual interpretation of the sample optic to the visual reference card.  The newer ISO standard applies a quantitative analysis based on the actual measured size of defects thereby removing any interpretation error.

In comparison, the ISO 10110 specifications provide a formula for precise sizes and frequency of occurrence for acceptable defects over a given area. This allows for the specification of smaller defect levels and makes the surface inspection process more quantitative and less prone to operator error (see comparison tables below).

Additionally, within ISO 10110, scratch sizes and dig are grouped together to reach the official surface quality per the formula below. Ng is the allowed imperfections within a grade class and A_g is the grade class selected.

While it may sound confusing, please use the attached references and reach out to us if you have questions. We are here to help— Sales@Escooptics or 800.922.3726