Many riflemen don't realize that scope tubes are not necessarily the same diameter. While the great majority of high-power scope tubes are 1-inch (25mm) wide, an ever-growing number are 30mm, a reflection of the influence of European designs, which frequently employ the wider tube widths. Schmidt & Bender and Zeiss have developed even wider 34mm tubes for scopes intended for .50-caliber rifles.
The 30mm tube (right) allows more light passage than a 1-inch tube.
The benefits of a wider tube are threefold. First, becausc the transmitted light need not "bend" so much when traveling down the tube, there will in theory be less distortion around the edges and a crisper image. Second, the wider internal lenses will allow the unhindered passage of more light, with a brighter view reaching the shooter's eye. Third, a wider tube allows more elevation A'lOAs for long-range shooting.
All these arc true to some degree, but not necessarily enough to make a lot of difference in performance. For example, there must be a boost of at least 10 percent in light before the human eye can detect any difference. And a good-quality scopc should have very little peripheral distortion anyway.
Still, if your budget can handle it, these 30mm tubes are better and worth having.
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