Telescope Reviews: Eyepiece cleaning woes

From least harmful/effective to most:
1) Water. Doesn't dissolve eyelash oils or pollen. Not recommended.
1a) Breath on eyepiece. Can't say why this is more effective than just water, but it is.
2) Pure isopropyl alcohol. Without soap added, this can't clean a lot of organic debris. Just not strong enough. Safe, though. Does a decent job on already fairly clean lenses.
3) Water/soap/alcohol mix (like ROR). Very effective to remove organic contaminants. Doesn't clean everything off eyepieces, though, without multiple cleanings. I had some thick mascara streaks that required several cleanings with something harsher.
4) Acetone. Much better solvent. Not harmful to lenses, but can dissolve plastic. If the cleaning is anywhere near a plastic baffle or rubber eyecup, don't use it. It's quite safe on all-metal eyepieces, though, and cleans off some stains that other cleaners can't.
5) Methyl Ethyl Ketone (MEK). This will take off ALL substances on the lens and requires ventilation for safety. It has removed mildew and chemical stains where nothing else would touch the discolorations. It won't harm the lenses with short-duration contact, but I only recommend it if the eyepiece has what looks like mildew or rust discoloration on the lens (likely to be a classic eyepiece being restored after disassembly).

It might interest you to know that I have tried, just for the sake of an experiment, cleaning brand new eyepieces right out of their boxes. Guess what? They got cleaner. Noticeably. It seems that many companies don't maintain perfect cleanliness in assembly one the eyepiece is put together. I've even seen a brand new eyepiece come out of the box with a fingerprint on the eye lens (!).

People on this forum are obsessed with picayune details that distinguish one eyepiece from another, but seldom address the possibility the eyepieces being tested might not be clean. Though one could become obsessed with cleaning, a judicious amount of cleaning at regular intervals or whenever anything foreign is seen on the lenses is definitely called for. Done right, no damage will result, and the eyepiece will be cleaner.

Most often, I see little tiny dots that probably are from the eyelashes touching the eye lenses or from accidentally breathing on the eyepiece lens. I don't let those sit because if left in place they can cause permanent damage to the lens coatings in time. But if there appears to be small shiny dots on the eyepiece, they are probably cleanable. The small dots I've seen that were where small dust particles present on the lenses interfered with the coating process were all invisible to the eye and only visible through a 20X loupe or microscope. I suggest you NOT inspect your eyepieces that way unless you realize that nothing is perfect.

If you get pure alcohol or acetone, make sure they are "reagent grade" or as pure as you can find. No additives. I've been able to find 90% pure IPA and 90+% pure acetone in local stores. ROR works great 99% of the time.