Originally Posted by salukipv1

According to cabelas scope buyers guide...

Tube Diameter: The majority of the scopes on the market come with the main tube having a one-inch diameter. Several European models and now a few others also come with a 30mm tube diameter. Contrary to popular belief, the larger tube does not allow more light to reach your eye. The exit pupil mentioned above controls this. However, a larger tube diameter does give added strength and rigidity due to the greater cross sectional area and larger rings and mounts. A larger tube diameter also allows for an increased range of adjustment for windage and elevation.

click on the buyer's guide to read more...if you want.
http://www.cabelas.com/cabelas/en/te...set=ISO-8859-1