Mark wrote: http://absoluteclarity.com/evaluating-your-stereo-… Mark, That is actually a pretty good SOP to setup for eyepiece parfocality. It is generally done once a year if everybody wears their prescriptions (contacts, glasses, etc) when using the scope. It doesn't address the camera port which requires a second diopter adjustment, and a third one is required if you have an internal lightpath reference reticle which would be the primary reference plane. If you remove the eyepieces, you can get dust and eyelashes in the ocular tubes but otherwise they are contamination resistant. To clean, first use a keyboard duster can or (old school) a squeeze bulb (looks like an ear irrigator) but never a compressed air line. Then Q-tips with rubbing alcohol or distilled water but never other solvents like toluene, MEK, acetone as they can attack enamels and cements. Tim