LENS MAINTENANCE.
The performance of the lens depends on careful maintenance. It is a high-precision optical device and requires very careful handling. Use a brush or a soft brush to wipe any dust or condensation off the lenses, cloth washed several times. The often recommended chamois leather is less suitable for this purpose, because the dust lingering in its pores, and sometimes small lumps, could scratch the surface of the lenses.
Non-reflective lenses now have such a hard anti-reflective layer, that they withstand gentle abrasion without damage, very soft, a clean cloth. However, lens cleaning should be limited to the exterior surfaces only. Cleaning the lenses from the inside of the luminaire should be entrusted to specialists, because they do it better and with a guarantee, that unscratched lenses will be correctly positioned when reassembling and the lens will not lose focus.
The threads in the lens mounts are right-handed. Do not overtighten them, as this can result in harmful stresses or even cracks in the lenses. If the thread cannot be loosened, put a drop of bone oil between its threads.
Occasionally you may notice air bubbles in the objective lenses. These defects in the glass are tolerable within certain limits and have very little influence on light loss and image sharpness. They are unavoidable in high-quality optical glass.