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Message: <blockquote data-quote="WJC" data-source="post: 4144097" data-attributes="member: 25191">This thread is full of talk about wavefront error and “Absam Ring.” So, I would like to speak up before this madness takes hold and ties up conversations for days or weeks, like so much smoke-and-mirrors has a tendency to do.First, I must admit my ignorance of the subject. Ed, Holger, Henry, Jan, Gijs, Joachim, others, could you please explain:1) Why in decades in the optics industry—having designed, manufactured, repaired, calibrated, and/or collimated instruments, having routinely spoken to hundreds of optical engineers, optics professors, and optical company CEOs, I have NEVER heard of an Absam Ring, before?In addition, when I typed “Define Chromatic Aberration” into my browser, I get pages and pages of definitions, examples, and associated reading material. Yet, when I typed “Define Absam Ring” I see ONLY 2 references related to a mention of Swarovski. Both originating with Birdforum and neither offering a definition or a point of origin. Doesn’t that seem a bit odd?And then we have seasoned observers who say they have never seen this anomaly—including some who have looked at an image that is supposed to illustrate it.Folks, optics are not created in a vacuum nor exclusively driven by the mathematics seen on a computer screen. Lenses held in a cell are PINCHED on the outer edge. That is just a reality of the matter and the gods of physics have found no need to alter their science because a few people of limited understanding on binocular forums need something to complain about.2) YES, an interferometer could tell you much about an optical figure and surface. But what would one do with that information? That’s an important question to ask, as it relates to reality or BB stacking and a reason to keep impractical conversations moving forward. An interferometer has a place when testing the figure and surface roughness of an expensive telescope that will be used at higher magnifications. However, using one to test binoculars is as logical as hunting squirrels with a howitzer.The attached photo shows an interferogram of an 8-inch telescope mirror. Horrible you say. But without the interferogram, the mirror looks just fine and you might be happy with the images it produced.Learning what is important in the REAL world in which we live is of great value. Those peaks and valleys look like they are separated by a quarter inch. They’re actually separated by MICRONS! A micron is a MILLIONTH of a meter.God, grant me the serenity to accept the things I cannot change, courage to change the things I can, and wisdom to know the difference.Bill[ATTACH=full]1367393[/ATTACH]</blockquote>

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