Keeping your Leica lenses really clean
For the lens barrel exterior, any soft cloth will do — no magic required. For the lens glass, use a microfibre lens cleaning cloth. First blow off stray dust with a blower bulb, breathe lightly onto the lens, and then wipe with the microfibre cloth until clean.
Where can you buy good quality microfibre cloths? Any camera store. Also (less obviously): opticians, pharmacies (for spectacles) or Sport Optics retailers (binoculars, telescopes, rifle sights etc.).
Not fanatically clean enough? Joe Codispoti provides the following tips:
The cleaning cloth provided with binoculars, telescopes and some electronic equipment is silicon impregnated and meant not for optical use but for polishing the hardware. It would indeed smear a lens.
[Regarding microfibre cloths for lens cleaning …] Leica cloth aside, which is more a "collectable" because of the name, there are two types which I consider the best: the one that looks and feels like silk made by Dustoff ($5.95), and ClearSight, which looks and feels like fine velvet and is completely lint-less ($4).
To buy the Dustoff and ClearSight cloths, lens cleaning fluid and brushes, see the following link:
Wondering about ROR ("Residue Oil Remover") and whether it is the "best" lens cleaning solution? Actually it isn't, mainly because it contains ammonia to cut through greasy fingerprints and stains. As you are probably aware, this stuff is toxic and corrosive! So use it very carefully, or better still, don't use it at all.