An optical assembly for an electro-optical reader includes a lens mounted in a stepped barrel. The stepped barrel has a barrel step between first and second barrel portions. The optical assembly is installed along an optical axis in a stepped chassis having a first chassis section that receives the first barrel portion with a slip fit in which a mechanical clearance exists between the first chassis section and the first barrel portion, a second chassis section that receives the second barrel portion with an engagement fit in which the second barrel portion frictionally moves against the second chassis section, and a chassis step between the first and second chassis sections. The chassis step is spaced away from the barrel step after installation of the optical assembly to bound a debris compartment to trap any debris resulting from the frictional movement of the second barrel portion against the second chassis section.