Akira Yabe design methods

Design methodology overview

Akira Yabe has created an optical design methodology that gives outstanding results, both in terms of sheer system performance and in manufacturability.

The core of the process is an efficient global optimisation. This is accompanied by an efficient zoom lens prototyping method.

Aspherics & glass selection are given special consideration, and the design is desensitised to manufacturing errors in order to give the loosest possible tolerances for manufacture, consistant with maintaining quality in the real systems.

Global Optimisation

The use of an efficient global optimisation technique enables Akira to find the best solutions [the escape function methodology is used]:

• The appropiate lens type is created automatically by the global optimization. The result of the global optimization does not depend on the starting point very much. For the most cases parallel plates are enough for the starting point.
• Only the glass count need to be given. By trying a few values of the glass count the appropriate glass count is determined.
• All the practical design conditions are included from the beginning. The quality of the lens is directly expressed by MTF.
• The global optimization with escape function is very fast and the result is reliable.
• This method works very well even for the zoom lens, aspherics, and DOEs.

Prototyping of zoom lens

Akira developed a unique prototyping method of zoom lenses.

• For the zoom system there is a wide variety of zoom types. With this prototyping method various zoom types are created systematically.
• Existing lens data is not necessary for the starting point of the optimization.
• The global optimization is then applied to each zoom type and the best zoom type is determined.

Optimal selection of aspheric surfaces

Akira developed a unique method to determine which surface[s] should be aspherised.

Aspheric surface numbers are extended to continuous variables and the best aspheric surface numbers are determined by the conventional optimization.

Accurate glass model and cost control

Akira uses the accurate glass model including the abnormal dispersion. With this glass model exotic glasses are used very effectively.

The glass cost is also controlled. This allows the minimum use of expensive glasses.

The specific gravity, transmittance, thermal coefficient, and thermal expansion are also modeled. The glass weight, transmittance, thermal characteristics are accurately controlled even at the stage with the fictitious glasses.

Sensitivity control

The sensitivity to manufacturing errors is controlled [including tilt, decenter, thickness error, curvature error, and surface irregularity] throughout the design. The method is applicable to both high NA & wide field lenses. The sensitivity to MSF (Mid Spatial Frequency) surface error is also controlled.

As an added bonus, no additional calculation time is necessary for this desensitisation.

Determination of tolerances

Tolerances are determined rigorously from the performance statistics. Account is taken of the manufacturing costs.

The final tolerances are verified and the distribution of the quality is assessed by Monte Carlo methods.

Tolerances with the lowest cost to fulfill the yield requirements are determined with a few trials of Monte Carlo simulation.

Optimal selection of lens count to each lens group

The optical system often consists of multiple lens groups to perform the zooming or focusing. Akira developed a unique method to determine how many lenses should be given to each group.

Group separation lens numbers are extended to continuous variables and the best separation numbers are determined by the conventional optimization.

The optical system with multiple lens groups can be optimized only by setting the total lens number and the total group number.