A sturdy metal housing protects the precision mechanical and optical parts against harmful external influences. Nitrogen filling prevents misting up of the optical system on the inside, even under extreme temperature fluctuations.
There are those who prefer straight viewing in a spotting scope, and those that prefer a 45-degree angle. There can be no absolute certainty of which is better for you until you try them. But that being said, it is commonly accepted that acquiring your subject with a straight scope is a bit easier than with an angled version. This is of paramount importance to a beginning enthusiast.
