I have always understood that the nitrogen was used during scope assembly to evacuate any moisture that was resident at the time it was screwed together. I don't think there was any intent to maintain a pressurized nitrogen environment inside the scope, otherwise I don't think the eye piece would have been removable, or even adjustable. Having said that, I also understand that nitrogen molecules are three times as large as oxygen, possibly reducing the rate the nitrogen would migrate to the atmosphere. Terry H.
