The bottom of the edge is where the focal point is, the top is where the lens ends. As the focal length of the lens gets shorter, the distance gets shorter also. Longer focus eyepieces have longer top barrels. Unfortunately, this is the result of making all eyepieces parfocal. If we extended the upper barrels and made then longer, we would lose some in-focus. This becomes a problem with binoviewers where little or no in-focus is left. The only other solution is to make them non-parfocal, in which case all the upper barrels can be the same length. I suppose we could add some grooves, but for the really short ones there would be no room left for the lettering. Any other ideas?
Roland Christen
Roland Christen