Originally Posted by
bigcountry
Totally false. Anything you can do to open the passage of light in between the objective and ocular lens, helps.
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