DIY 2.5x to 5x Opera/Concert Glasses
Introduction: DIY 2.5x to 5x Opera/Concert Glasses
In July, I am going to see a concert at an outdoor amphitheater. I knew I was sitting at a fair distance from the stage, so I wanted to have a set of opera glasses so I could see the show up close. I have a very nice set of zoom binoculars, but they are heavy and are difficult to hold steady for an extended period of time.
This Instructable shows the process I went through in order to build my own set of Opera Glasses!
Supplies
* 3D Printer
* Two convex lenses
* Two concave lenses
Step 1: What You Can Buy (and Why I Chose to Make My Own)
On Amazon, they sell several hands-free opera glasses. I decided to buy one that was advertised at 3x magnification to try out. 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. For anyone who does not wear glasses, or has limited vision correction, I would recommend them, but they did not work for me.
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. If these specifications were correct, they would solve my problem. As it turned out, the second specs had the exact same magnification and range as the first one. The second seller was obviously lying, which isn't uncommon on Amazon. 215
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. For 10x magnification, you would need an extremely long telescope tube!
At this point, having rejected some of the commercial offerings, it was fairly clear that I would need to build my own!
Having these gave me a good baseline on what to expect for my build. From the glasses I bought, I measured the following characteristics:
* 30 mm objective lenses
* 12 mm ocular (eyepiece) lenses
* 40 mm of length
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.
Step 2: Researching How Binoculars and Opera Glasses Work
The first step, is to understand how binoculars and opera glasses work. Both of these devices allow you to see things at a distance, but they are designed differently and for different purposes:
Binoculars:
* Multiple lenses and prisms per eye
* Complex construction
* High magnification, narrow field of view
Opera Glasses:
* Two lenses per eye
* Simple Construction
* Low magnification, wide field of view
As it turns out, building opera glasses is very simple. They consist of a convex and a concave lens separated by a distance. Their construction dates back to <PERSON> and and opera glasses are a kind of Galilean telescope. The following page gives an explanation, and most importantly, provides formulas for computing the magnification and lens separation:
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/...
Figure Credits:
* https://en.wikipedia.org/wiki/Binoculars#/media/File:Binocularp.svg (CC-BY-SA 3.0)
Step 3: Choosing the Right Type of Lens
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 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).
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 convex lens, which points towards the object we want to see, is known as the objective lens and its focal length is designated fo (this number is positive). The concave lens, which sits close to our eye, is known as the ocular (eyepiece) lens and its focal length is designated by fe (this number is negative). 441