What is immersion oil used for and what is the proper technique for using it?
Most manufacturers recommend the following: Moisten a Kimwipe®* or piece of lens tissue with a small amount of alcohol (ethyl or isopropyl) and wipe the lens gently in one direction. Never apply alcohol or any other solvent directly to the lens as it may work its way into the mechanism and cause unseen damage.
Immersion oil should always be wiped from all surfaces immediately after use. In the event immersion oil is allowed to harden, moisten a wipe with a small amount of xylene and use this to redissolve and remove the hardened oil. Note, xylene may leave a film on the lens and may dissolve the cement used to seal the immersion objective. To prevent this, always moisten a second wipe with alcohol and use this to remove any residual xylene.
* (Dry, unmoistened Kimwipes are not recommended for routine lens cleaning.)
When replacing lamps or bulbs, avoid touching the glass with bare fingers. Fingerprints left on the bulb will actually "burn into" the glass and reduce the bulb quality and life expectancy.
It is a good idea, on a weekly basis, for the scope user to put the focusing mechanism through its paces. During normal use the mechanism is probably not worked through its full range of motion. Lubricating grease can build up and harden because it does not remain evenly distributed. To remedy this, rotate both coarse and fine focus knobs from end-stop to end-stop several times. Be sure to rotate the lower power objective into place before carrying out this procedure.