For anyone with difficult to clean coated optics I suggest trying this stuff. It works wonders, beats the "soapy water from the optician/camera store" stuff hands down & is safe for optical coatings of all types.
http://www.ror.net/
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Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”