The most commonly used standard for optics manufacturing is ISO 10110, which was first created in 1927. Below we will describe some of the key parameters called out in the standard.
The image below is a of a typical lens drawing.
The drawing can be divided into two areas – Drawing Area and Table of Parameters.
Let’s review the drawing area of the biconvex lens seen above.
You can see a set of numbered parameters and conventional signs which are described below.
- Lens diameter – full lens diameter.
- Lens thickness – thickness of a lens along axis of the base surface.
- Lens edge thickness. This parameter is given for reference. Its value depends on set of defined (with tolerances) parameters.
- Surface texture – composite conventional sign with set of parameters which defines quality of surface processing.
- Datum surface – surface which define datum axis of the lens. It is possible to see more than one datum surface on different drawings.
Table of parameters area
Table of lens parameters is divided into columns.
We can see two columns with requirements for the surface and one column with requirements for the optical element material in example drawing.
Column with surface parameters
- Radius of curvature value. Convex (CX) or concave (CC).
- Effective (clear) diameter – diameter is meant for light propagation. You should remember that optical coating is overlaid only in border of effective diameter.
- Protective bevel.
- Optical coating of the surface – should be meant working wavelength or set of wavelength or spectral range and coefficient of transmitting efficiency in percent.
- Tolerances on surface form (figure error). First number is the power difference in fringes. Second number (in brackets) is irregularity in fringes. Also wavelength for measurements should be defined.
- Centering – tilt angle of a surface defined as angle between the datum axis and the surface normal. Units – angle minutes and angle seconds.
- Scratch and dig specifications – there is defined all possible surface imperfections.
- Damage threshold of laser irradiation. Generally speaking, this parameter is critical for optical elements which work with high power laser irradiation. This is why this cell often is empty for the rest optical elements.
Column with material requirements
Column with material requirements is placed between columns with surface parameters.
It includes the following items.
- Optical material Name.
- Refractive Index.
- Abbe Number.
- Stress Birefringence – defines maximum allowable stress in nm/cm of optical path length.
- Bubbles and Inclusions – defines number and size of bubbles and inclusions in the optical element.
- Inhomogeneity and Striae – defines homogeneity class number and striae class number.
All requirements and properties of optical elements are defined by optical and mechanical engineers in the course of preparing an optical design.
Even with a published standard there can be confusion and different interpretations, so a best practice is to check with your lens manufacturer about their definitions and questions. For more information, one of the best and most complete online documents to understand this subject is available here.