Looking For Cheap Doublets

Paragon19 · Joined: 26 Dec 2021 Posts: 45

I'm planning to do an experiment with several different kinds of LOCA (Liquid Optically Clear Adhesive, and I'm planning to share the results on the DIY board here), and obviously to do that experiment I need some glass to glue together. So I'm just wondering if anyone here is aware of any cheap lens doublets that I can easily get in a quantity of about 6-10 identical units. They can be used, they can be from adapters, converters, cell phone clip on lenses, anything really, as long as they're made of two cemented glass elements.

Paragon19 · Joined: 26 Dec 2021 Posts: 45

Alternatively, I see I can quite inexpensively obtain single convex and concave lenses. If someone here is able to explain the measurements/terminology necessary to order complementary single elements that will mate flush, I can just go that route.

visualopsins · Expire: 2021-06-22

https://www.edmundoptics.com/knowledge-center/application-notes/optics/understanding-optical-specifications

Paragon19 · Joined: 26 Dec 2021 Posts: 45

kds315* · Expire: 2021-03-09

https://www.surplusshed.com/

They have them in various types and focal lengths ... cheap!

Paragon19 · Joined: 26 Dec 2021 Posts: 45

Paragon19 · Joined: 26 Dec 2021 Posts: 45

Well thanks to kds315* I was able to purchase 6 sets of uncemented achromat doublets, all with a focal length of 105mm, and diameter of 37mm, to practice using adhesive.

I have also purchased 4 different types of LOCA; Norland NOA 61 (from EdmundOptics.com), Xfactor Hydro XFUV10BLK, MMOBIEL TP2500, and Octopus Glue (all three of those from Amazon). I'm probably going to get some actual Canada balsam as well, for comparison, and to practice with separating after adhesion.

My intention is to test all of these LOCA against each other, looking at transparency, viscosity, propensity for bubbles, ease of application, working time, curing time, difficulty of separation/removal, and overall value for money. NOA 61 has been in use for quite awhile as a high quality LOCA for many different applications, so it's probably the adhesive to beat in the test. The three LOCA purchased from Amazon appear primarily designed for cell phone repair (gluing displays to glass digitizers), so it will be interesting to see if they appear suitable for lens repair as well since they're more budget friendly than NOA 61.

My next step is to devise a method for centering the elements before adhesion. My current plan is to use a battery operated turntable, center and attach an LED or laser (red to avoid any UV that might prematurely cure the glues), then center and attach a glass element holder, and use a bamboo chopstick to gently nudge the element in place. Centering all of these components will be achieved by projecting an image of the light source on a piece of paper suspended above the entire setup. When apparent rotation of the projection has ceased it should mean the element's vertex is centered. My intention is to do this as inexpensively as possible, as a demonstration for anyone else thinking of attempting these repairs at home. I haven't decided whether to bother centering the achromat doublets during the LOCA test. It would probably make good practice though.

I'll start a new thread in DIY once I actually begin the project.

RokkorDoctor · Joined: 27 Nov 2021 Posts: 920 Location: Kent, UK

Really looking forward to seeing the results, I would be interested in a feasible DIY centering setup myself.

Interested to see how you devise a turntable setup that allows for light transmission; I always assumed any DIY attempt at that would have too much play/runout in the bearings to be of practical use, as the wobble circle of the transmitted light should be quite small (ca. 0.1mm in the example of a 50mm focal length lens with unity magnification of the optical test setup, allowing for a 10 arc minutes decentering tolerance).

As I understand it, decentering tolerances are usually in the order of some angular minutes, down to some angular seconds for high precision optics (source: Christoph Gerhard, 2018, see below) Very interesting read that book by the way, one of the few commercially available books that focus on lens manufacturing as opposed to lens design. To be sure, camera lenses are not high precision optics in this context Wink

.

Useful references for cementing lenses (both still in print as of Jan 2022):

- Optics Manufacturing, Components and Systems", Christoph Gerhard, CRC Press, 2018 (cementing with modern cements)
- Prism And Lens Making, Second Edition, F. Twyman, CRC Press, 1952, 2017 (detailed info as to how to prepare Canada balsam solutions for cementing, and on balsaming jigs)

Paragon19 · Joined: 26 Dec 2021 Posts: 45

RokkorDoctor · Joined: 27 Nov 2021 Posts: 920 Location: Kent, UK

Paragon19 · Joined: 26 Dec 2021 Posts: 45

Very useful information, thank you. I have already purchased laboratory grade Canada Balsam in Xylene from Carolina Biological (I live the next city over from them, and even know someone who actually works there), so I'll give that a try first. I'll probably try baking some and record the appropriate temperatures and bake times. Since I'm using these surplus doublets that have no intended use afterward it really doesn't matter how they turn out anyway. I may have to order a few extra though, for the balsam testing.