To build a Galilean telescope, you need to know that lenses are described by a focal length, which is a distance, usually expressed in millimeters. The difference between these two lenses is that the convex lens bulges out towards the center while the concave is narrower in the center (it "caves in" towards the center). Our concert glasses, being based on a Galilean telescope, will make use of two lenses per eye, a convex lens and a concave lens. The focal length of the lenses isn't something I could measure, but later on we will see that I came up with some fairly good approximations and found out why 3x is the magnification limit for these glasses. From the glasses I bought, I measured the following characteristics: Having these gave me a good baseline on what to expect for my build. For 10x magnification, you would need an extremely long telescope tube!Īt this point, having rejected some of the commercial offerings, it was fairly clear that I would need to build my own! In retrospect, knowing what I now learned about optics, 3x magnification is the best that you can hope for opera glasses small enough to fit on your head. The second seller was obviously lying, which isn't uncommon on Amazon. As it turned out, the second specs had the exact same magnification and range as the first one. If these specifications were correct, they would solve my problem. I ordered a similar style of hands-free opera glasses from a seller that claimed theirs had 10x magnification and a focus range of -12 to 5 diopters. For anyone who does not wear glasses, or has limited vision correction, I would recommend them, but they did not work for me. They were well built, nice and sturdy and fit me well, but I am severely nearsighted (-6 diopters) and the focus adjustment would bottom out before I could get a clear image and I couldn't wear them over my glasses. I decided to buy one that was advertised at 3x magnification to try out. On Amazon, they sell several hands-free opera glasses.
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