Eyepiece endcaps

[Roy Challen]

main reason for dust and dirt on the lens is quite simply us - our sweaty eyebrows, bits of flaky skin, not to mention dandruff

Completely agree with this. I do a lot of microscopy at work and its the same there - forever blowing organic detritus from inorganic samples

[Roy Challen]

Not that I'm overly sweaty, flaky or dandruffy

[RikM]

I am afraid I'm not going to risk several hundred pounds per eyepiece for the sake of a couple of seconds to put the caps back on.

All kinds of dust and grit can blow into the EP case while it's outside, which would then be rubbed into (scraped across) the eyelenses of my EP's when taking them in and out of the box. Since I wear glasses to observe, I have the eyecups dialled all the way down, so the foam would definitely rub on the lens. I swap EP's a lot while observing, so to me, it is a very real risk.

When I clean my EP's—needed no more than once or twice a year—I use a hurricane blower and then Baader fluid and clean microfibre cloths. I also clean out the dustcaps.