DIY Element Alignment Project

Paragon19 · Joined: 26 Dec 2021 Posts: 45

Now begins the tale of the experiment that spawned preceding experiments. In my quest to acquire the ability to adequately cement lens elements, I realized first that I must journey down the paths of learning both to separate elements, and align elements as well.

Bear in mind as we continue that I have essentially no experience or specialized knowledge in these subjects or skills. To those of you here who actually do have the kind of knowledge and skills this requires, I would love your input. I'd really like to hone a reasonably accessible DIY method for aligning lens elements, and any information or ideas you, or anyone else here have would be greatly appreciated. If you notice me screwing something up, please say so, I fully admit I know very little about what I'm doing.

All that said, the idea is simply to use a laser pointer to locate and align the centers of curvature of the lenses during the cementing process, using a setup a little bit like this:

Today I actually got around to combining all the pieces I accumulated to do a first run, and...it was a failure. That's okay, I expected to need some revision, that's where I'm hoping some of you can help out. Here are the parts assembled so far:

First we have a "heavy duty swivel turntable", a heavy glass plate, and a small mirror.

Next have a laser bore sighter, this one designed for 12-gauge shotguns, some vacuum pad lens tools, and an uncemented achromat doublet (six identical doublets total, actually), sourced from Surplus Shed.

The operation is fairly simple; the laser pointer is put on the turntable in the center, and then a target is suspended above it with some sort of reference mark:

To get the laser centered, the turntable has to be rotated. As it rotates the laser will trace a circle on the target, with a radius the same as the laser's distance from the true center of the turntable. Then the laser is to be gently tapped into place until the rotation is no longer marked by a circular path.

Here, unfortunately, I hit the first stumbling block. For starters, we don't actually have any assurances the laser's path is truly vertical the way it's standing on the plate. The mirror is added to try and provide a level surface, but the laser itself may still be shining at an angle. The first workaround I have planned to account for this is actually to mount the laser pointer on silly putty, or perhaps something a bit stiffer yet still malleable, to allow the angle of the laser to be gently adjusted as well.

Compounding the issue, however, is the turntable itself. For starters, the turntable chosen does not sit or remain completely level, due to the soft feet on both top and bottom. Second, the actual motion of the turntable itself produces a wobble, which makes it hard to tell how well the laser has been centered.

Ideally however, once the laser is centered, a lens element holder is to be placed around the laser, to allow the beam to shine through the lens elements. Each element is then to be gently tapped into place as the turntable is again rotated, until the top and bottom centers of curvature are aligned. Once the first element is aligned, LOCA is to be applied, and then the second element is to be added, and again gently tapped into place until both of it's centers of curvature are aligned as best possible with the lower element.

The previous three images were taken simply as an illustration, and were not properly aligned, but here still you may have noticed the second stumbling block in the way the lenses are supported, and the fact that they are not level, and the extension tubes are also not aligned to keep the laser in the center. Part of the problem is the vacuum pad tool I'm using as a support, instead of something that can attach to the extension tubes integrally. I also found the material kept a bit too much grip on the glass.

So right now I'm looking for ideas for a more suitable turntable with less play and variation, as well as a more suitable support of a small enough diameter to support the lens elements, and soft enough material to avoid damaging the glass, but still allow the element to be shifted as needed for alignment. My current ideas are a small rotary table, and a plastic tube support for the lens elements, something with a heavy and wider base, to prevent toppling and shifting. I'll also need to devise a way to access the laser while the lens holder is still in place.

It's not exactly a lot of progress yet, but again, here I hope I might be able to get some assistance with brainstorming or part sourcing. I'm sure there are some more appropriate components I could be using, and that someone here should have an idea of where I can get them, much the way kds315* pointed me toward Surplus Shed when I asked for doublet sources. Otherwise, more progress to be posted once it has been made.

Paragon19 · Joined: 26 Dec 2021 Posts: 45

I just woke up in the middle of the night and had the realization that multiple levels of a translucent material would make it easier to check the the angle of the laser during calibration. I also realize now I'm going to need to construct a base and arm on which to attach the rotary table and reference point target, which should not only help minimize beam movement due to vibration or other sources, but also hopefully decrease re-calibration time and allow me to clamp the alignment station to my work space.

I'll probably sketch a diagram of the idea in the morning. It helps me fall back asleep to put my thoughts down somewhere so I don't need to keep thinking about them, and what better place than this thread?

RokkorDoctor · Expire: 2025-05-01

The theory of a lot of what you are doing is fine; professional setups will have a lot of these elements. Smile

I admire your courage & perseverance; as you are discovering, a few problems are to be anticipated in the DIY arena:

1) Bearing stability of the rotational platform. This needs to be very accurate. Professional setups often employ air bearings, the lazy-susan ball bearing you are using I very much doubt will be accurate enough for centering purposes. I would suggest you really want less than 10 microns play even for a DIY setup.
2) The whole setup needs extremely good stability. Professional setups employ very stable column mounts, if you are going to have to go the tripod route then do get rid of any rubber feet etc. and use metal spikes on a stable and flat hard surface etc.
3) For centering lenses you will need to collimate the laser output of the doublet to be centered. E.g. if you were to want to center a doublet of negative power, you will need additional optics to re-collimate the laser beam onto the target.
4) Professional setups have high magnifying optics, so the wobble is magnified significantly for both ease of observation as well as aiding quantification of the residual centering error.
5) Once the first lens (say the crown e.g.) has been centered, you will need a way to lock it into position, so that when you tap the flint into position, you are not disturbing the crown lens. I believe professional setups use a vacuum suction process to do this, but I could have that wrong.

Other than the stability issues that you need to address, I think you will also need additional optics to address 3) and 4).

It almost feels as if a microscope frame would be a better base to start from.

Good luck, admire your enthusiasm! Like 1 small

Paragon19 · Joined: 26 Dec 2021 Posts: 45

Very useful input, thank you!

RokkorDoctor · Expire: 2025-05-01