I have designed an imaging lens assembly incorporating two plastic lenses. The first is Zeonex E48R and the other is PMMA. The manufacturer has supplied the lenses well within tolerance, including the surface irregularity P-V. I have remodelled the system incorporating all supplied component tolerances and surface irregularities and i am never getting above a 50% MTF contrast of 50lp/mm compared to the design value of 110lp/mm. The worst case modelled MTF over 1000 Monte Carlo runs is 80lp/mm. Note that i have also included the lens barrel tolerances in the model.

Any suggestions as to what could be causing the further consistent loss of MTF, particularly wit plastic lenses? The lenses come from several tooling cavities, but this has no impact on the results. Illumination is at 850nm and the transmission of the filters used has been confirmed as correct.