Steve Kelley | In world of NFL coaching, Jim Zorn has arrived. Originally published November 24, 2008 at 12:00 am Updated November 23, 2008 at 10:15 pm. On Sunday, as the Seahawks lost for the ninth time in 11 games and the fourth time in a row, it is worth taking a moment to celebrate Jim Zorn's success. Share story.
Eye relief refers to the distance between your eye and the lens at the rear of the scope that will give you a full crisp view, no dark ring around the edges. Important to know for high recoil calibers to avoid a black eye or worse. Some scopes are single power (3Ã32, 4Ã30 for example) which means no adjustments.
Eyepieces have a focal length too. To use an eyepiece with a telescope, the eyepiece is mounted so that the focal planes of the telescope and the eyepiece are in the same location. Focal ratio, or f/ratio, is the focal length of a lens or optical system divided by its diameter. A telescope with a lensor mirror `that's 90mm in diamter and has a 900mm focal length has an f/ratio of f/10. But what does this mean? F/ratio isn't a measure of quality. There are good f/15 scopes and good f/3.3 scopes. Varying the f/ratio allows designers to trade off different scope characteristics. For example, for a given design, the lower the f/ratio, the smaller the scope. But at the same time, the longer the scope, the easier it is to achieve good optical performance.