TOLR allows you to target the as-built performance of your lens directly. The only downside is that it is more computationally intensive than the traditional method, and so the optimization time is longer. The payback, however, is that the design so produced is much less sensitive to perturbation.

In order to get good results in as short a time as possible, the following are good practice:

1. Use a multiple-processor machine. ZEMAX can support up to 16 CPU cores in a single machine, and support for more will be added as the hardware becomes available. Ray-tracing speed scales linearly with the number of processors (with a small overhead for managing the multiple processors).
2. Produce a reasonable starting point first. Tolerancing cannot begin until the design is exceeding its required perfromance. Accounting for sensitivity to manufacturing errors is unnecessary during the early design stages.
3. Run an initial sensitivity analysis, to determine if any tolerances are insignificant. It takes as long to compute the sensitivity of a design to an insensitive parameter as it does for a significant one! In the doublet used here, the design is most sensitive to tilts and decenters of one element with respect to the other, and has almost zero sensitivity to the glass refractive index changes. Intelligent pruning of the tolerance list can greatly reduce the calculation time.

Summary

TOLR is a very effective way to design a lens, taking into account the tolerances introduced by the manufacturing process.