Optical assembly includes mechanical and sometimes electronic elements. In the latter case, electrostatic discharge (ESD) means should be considered to protect the electronic devices. Visual inspection to assess the completeness (without causing mechanical damage) of the assembly should also be conducted. During the cleaning process, special care must be taken regarding how the lens is connected to its housing—with a fastening nut or with room-temperature vulcanizing (RTV) silicon (a type of silicone rubber made for a two-component system):

• If the lens connected to its housing with a fastening nut, special care should be taken when cleaning the lens to not let the cleaning solvent penetrate the screw thread of the fastening nut. Clean with as little solvent as possible.
• If the lens is connected with RTV silicon, do not use cleaning solvents that might dissolve the RTV. Use isopropyl alcohol or ethyl alcohol (ethanol), not acetone.
  This treatment applies to new and used assemblies

Elements that undergo maintenance are used elements; the cleaning procedures are the same as those for cleaning new elements with an emphasis on three issues that refer specially to outer elements (lenses, windows, domes):

• The coating may be damaged or weakened due to environmental exposure and/or improper handling, and might peel during cleaning.
• Different kinds of dirt and stains may be attached to the surfaces in such a way that conventional cleaning procedures will hardly affect them.
  This situation requires patience and repeated cleaning with different cleaning solutions.
• Damage, such as scratches, digs, and cracks, should be treated according to the existing organizational procedures (measuring, reporting, decision making, and implementation)