MicrobeHunter.com Microscopy Forum

Hello.

I need good advice on how to clean a 400x objective lens which has become dusty and oily.

The lens has anti-fungal coating which I do not want to remove if possible. Can anyone give me any good and sound advice?

That would be much appreciated.

I believe you refer to a 40x objective.
Wipe the oil layer with a lens tissue or Kimwipe. A single movement, not a to-and-fro wiping. Fold the paper in twice, repeat the wipe. Do it gently. Avoid overdoing. Inspect the lens through an inverted eyepiece (hold the eyepiece close to the objective lens under side-light). When the oil is removed, exhale on the lens to form a condensation layer, then wipe once more with the tissue.
If absolutely necessary, the oil sticks to the glass etc, moisten a Q-tip with light petroleum (or heptane, octane, iso octane) and wipe the lens once.
NEVER use toluene, paint thinner, acetone, bleach, kaustic, fungus remover, other cleaning strong chemicals.

Q-tip moistened with 70% - 90% isopropanol (rubbing alcohol) works fine. Gently, with a circular motion, center to outer area. Don't reuse the Q-tips. Several passes, gently, if necessary to remove the oil and other junk. It usually takes me a half-dozen or so passes, fresh Q-tip each time, to get an oily lens clean. Sometimes more. 70% tends to leave a little residue you can get off by moisture from your breath and another gentle Q-tip wipe. 90% tends to dry with much less residue. As Hobbyst46 said, use a reversed eyepiece as a magnifier to inspect the lens to be sure you've completely cleaned it. Look for light reflections on the surface of the lens to be sure there's no residue. Same technique for cleaning eyepieces, except I usually use a small cotton ball instead of the Q-tip.

If you use lens cleaning tissue - I almost never do - drag it across the lens without finger pressure. Keep your fingers off of it so you don't trap debris under it and drag it across the lens under the tissue. You can badly damage your lens that way.

Did I mention do this GENTLY?

Try to get into the habit of always moving the objective turret in one direction, lower magnification to higher, and NEVER go from an oil lens to a dry lens without cleaning the oil from the slide first. Otherwise you will get more oil on the 40x from the drop left on the slide.

Ok, thank you for your advice.