I haven’t cleaned my compact ACOG yet.
For scopes, binoculars, etc. I typically flush with copious running water, followed by very gently rubbing the lens with tissue paper (obviously without Aloe, perfumes or such on it) while using more running water.
I follow with Birchwood Casey Lens cleaning fluid and more tissue. I probably should use lens-cleaning paper, but the tissue seems OK.
While I’ve never had a problem, I guess water in some parts of this country might be unsuitable for this. In any event, you certainly don’t let the water dry out on the lens.
To me the most important thing is to loosen and wash away get every last speck of grit before applying any pressure to the lens. That grit will scratch a lens. Beware of grit that hides along the edge of the lens only to later become embedded in your cleaning tissue. Change tissue constantly, this is the wrong place to try to save a few cents.
Even when the grit is gone, use only light pressure against the lens. If you use tissue like I do, remember it may have grit, etc. in it as it comes out of the box – it’s made for blowing noses, not cleaning lenses. Toilet paper strikes me as being a little too coarse for this use – it’s designed to be strong, not soft.
The lens cleaning fluid should remove any oils on the lens.
Take your time and be fussy; one careless cleaning and you’ll have a scratched lens forever!
I don’t quite trust the Lens-Pen. It looks to me like it’s designed to remove smudges, not dirt.
Dust can be removed with a lens brush like photographers use on their cameras. Incidentally, camera shops carry serious lens cleaning equipment.
I put a sandwich bag over my ACOG when cleaning and when storing the rifle. I’ve heard that bore solvent can damage the lens coatings.
As much as an ACOG costs, you’d think they would give you some lens caps!