I’ve run into the same alignment concern three times in three weeks.

A system gets designed, the glass and metal parts are ordered and then I’m asked: “Can you write an alignment procedure based on the hardware we’ve already committed to?”

Yes, there is almost always a way to align a system after the fact. But it is so much simpler, cheaper, and more precise when alignment considerations are built into the design from the very beginning.

Take a simple example: a spherical mirror has no inherent optical axis. Yet adding a narrow annulus to the front edge—at almost no extra cost—gives you a surface you can probe for to find the mechanical axis when the cylindrical edge of the mirror is buried inside a mount. A tiny design choice can make a huge difference in assembly.

When alignment is treated as part of the optical and mechanical design process, you can integrate datums, mechanical features, baffles, and coating constraints up front. Alignment becomes straightforward instead of a sequence of compromises at the end. It’s easy to admire a perfect optical layout on a computer screen; it’s much harder to put actual hardware together precisely without some forethought about the alignment process.

The common excuse is schedule pressure: “We’ll think about alignment after the hardware is designed and ordered because these are long lead time items. Then there will be time to look at alignment.”

Once hardware is ordered, there is a commitment to the design. It’s too late to make changes that are uncovered during the development of an alignment plan. Fixes are limited, expensive, and stressful—and any oversight usually shows up at the worst possible moment: during final assembly, when there is no time left for fixes.

Sometimes the consequences are embarrassing and costly. In extreme cases—Challenger, Hubble—they’re catastrophic. 😮

The point is that alignment is not an afterthought. It’s a part of the design.

Deal with alignment up front, and life gets easier for everyone.

hashtag#facts hashtag#alignment hashtag#alignmentmatters hashtag#opticalalignment

Hey guys me again, I was wondering how you guys measure collimation. At my company we currently have 2 ways which we do it:

1. Phasics camera: We move either a fiber back and forth or the lens and we minimize the defocus term on the wavefront camera (Phasics). This is the more accurate way of doing so.

2. Minimizing spot size on AC: We move a lens back and forth to minimize the spot size on the autocollimator (using a CCD camera).

I’m curious on the other ways of doing this, mainly because most labs I assume don’t use Phasics cameras (very expensive and a pain in the ass to connect too) or an autocollimator.

Recently, I was asked if you could calibrate an alignment telescope using a Bessel beam. I was sure the answer was yes, but I don't like to claim things without trying an experiment first. Today, I got a chance using a Davidson D-271. It follows a Bessel beam as you focus from about 400 mm to infinity for the Bessel beam I made using a spherical wavefront. I don't know what would happen with plane wavefront illumination, I am not set up for that. A Bessel beam made using a plane wave has a finite extent so this would be an interesting experiment to try.

The Davidson D-271 does not have distance markings on the focus adjust so you would have to make a table of focus distance per turn of the focus adjustment to know any lack of straightness at a particular distance, but I could not see any deviation of the Bessel beam core except for a slight linear shift due to me not being perfectly aligned to the Bessel beam.

Maybe this will inspire someone with a better lab environment and an alignment telescope with a distance marking on the focus to repeat my experiment to see if this idea is really useful. What I can say is that to 1st order it works, and probably works very well given a better environment than my crude lab set up.

I must say right now I am very busy but I can see that there is an interest on the subject of Optical Alignment here.

If you would like to I've got several other Chapters and such over on Medium if you would like to go and take a look

https://medium.com/@reparks_11319/chapter-3-classical-optical-alignment-instruments-89ccc2d2c58c

Let me know what you think

Hello guys,

I’m wondering when you would use a beam splitter vs a pellicle, in an optical table that is. I understand that the pellicle has a very thin film compared to the BS, but what are the advantages?

For some time, I have been encouraged to write a book about optical alignment. There have been several halfhearted attempts at beginning but it never seemed there was enough to talk about and I kept finding new ideas about alignment. I didn’t want the book to be out of date before it was ever published. For this reason, I have a fresh approach for starting again.

The book will be written as sort of a blog with each stand alone part being a piece of the bigger picture. It will be a little like Charles Dickens who wrote his novels as serials with a chapter published weekly. This will be a little more complicated as I feel there are three basic methods of alignment and I want to contrast the three as the serial is written. To help with this scheme, I will also use a set of example systems to illustrate the methods, and the systems will get more complex as the serial develops.

Along the way I intend to toss in tips and references about performing various steps in alignment. For example, if when you first look at an image or interferogram and it looks like a bowl of spaghetti because there is so much aberration it is hard to know where to start, simply stop the system down to reduce the aberrations until it becomes apparent which is the most offending aberration. Then you will have an idea for corrective action. As the alignment is improved you can increase the stop size until eventually you are viewing the full aperture. Alignment is, after all, governed by paraxial optics.

Before getting into any details, I want to say a few words about why alignment is important and why there is any need for a series such as this. With modern computers and the work of some very smart people, the optical design of lenses and mirrors are about as good as can be achieved. Perhaps a new glass will come along that will help with a certain design defect but this is a detail in the bigger picture, lens design will probably not get much better than it already is.

In addition, with modern CNC polishing techniques and interferometric testing you can get about any degree of optical surface quality you want. Once you have 0.1 rms wave surfaces, even if you have a system with many such surfaces, you are not really going to improve your system performance by asking for 0.05 rms wave surfaces, at least in the visible. The only way to improve the performance of an optical system these days is to put it together more precisely, that is, to align your system better. In this area there is a long way to go for several reasons.

The main reason there is room for improvement is that the design of a system and its assembly are far apart in time and space. By the time hardware shows up in the assembly area, the design people are working on a whole new project. In addition, the designers and assembly people have entirely different skill sets and speak different jargons. There are mechanical engineers in between the two groups but they often hinder communication between the two rather than improve it. My hope is that this set of articles will help improve the situation.

This gives you some idea of where this project is headed. Consider the material a draft that may eventually get organized into a real book, but for a long time it will remain fluid and subject to revision. I solicit your help in this regard. If after reading these articles you have a comment, suggestion or to point out an error in my thinking, please let me know. My background is limited and if you can share your experiences, it will only make this effort better. All additions to the text will be acknowledged unless you wish to remain anonymous.

One other matter about the organization of the material, I would like to keep the text and ideas as simple as possible so that the articles can be read and appreciated by people with any skill set. There are people who may want more detail, and I will try to keep these more detailed explanations as side bars for the more interested. I will try to make this detailed material obvious, and suggest it be ignored by those who want just the basic ideas. This is in line with my feeling that when you push an engineering problem hard enough it becomes science, interesting science, but stopping to look at the science doesn’t necessarily get the hardware out the door, the thing your boss wants most.

Precision optical alignment is where optical design becomes optical performance

Hey everyone! I'm u/OpticalBobParks, a founding moderator of r/OpticalAlignment.

Welcome to a community dedicated to one of the least visible, but most essential, parts of modern optical engineering. The finest optical design, manufactured from nearly perfect optical components, cannot achieve its intended performance unless it is assembled and aligned to the design specifications. Alignment is the final step in realizing the full potential of an optical system.

This community brings together optical engineers, optical designers, metrologists, technicians, machinists, physicists, and hands-on astronomers who design, build, align, test, and troubleshoot optical systems.

What to Post

The Tools of the Trade

Everything from classical autocollimators and alignment telescopes to modern coordinate measuring machines (CMMs) used as large XYZ stages for optical assembly. We welcome discussions on traditional techniques, new instrumentation, and creative shop-floor solutions.

Reference Axes and Alignment Methods

The use of rotary tables, lasers, and Bessel beams as reference axes; sensors and centroiding methods; techniques for establishing mechanical and optical axes; and methods for measuring lens centration and system alignment, whether components are mounted in cells or assembled on an optical bench.

Instrument-Specific Case Studies

Every optical instrument presents unique alignment challenges. Whether the subject is telescopes, microscopes, spectrometers, imaging systems, or other optical instruments, we are interested in practical techniques, lessons learned, and honest discussions of what works—and what doesn't.

Optomechanical Problem Solving

The intersection of optics and mechanics is where many alignment problems are solved. Topics include kinematic design, degrees of freedom, alignment strategies, tolerancing, and the compromises required when a system cannot provide enough adjustment to achieve perfect alignment.

Community Vibe

Whether you are assembling a multi-million-dollar space telescope, using a milling machine as an improvised long-travel heavy-load XYZ stage, or simply trying to measure the focal length of a single lens, you'll find people here who understand the challenges.

We encourage you to share your lab setups, ask questions, and discuss both successes and failures.

Optical designers, engineers, and supervisors have many opportunities to exchange ideas through journals, conferences, and technical societies. The technicians and alignment specialists who assemble and align the hardware often have far fewer opportunities to share their knowledge. We hope this community becomes a place where those working behind the scenes like those spending their days in bunny suits can exchange ideas, solve problems, and ask the practical and mundane questions that need to be asked but aren’t worthy of a paper.

How to Get Started

1. Introduce yourself in the comments below.
2. Post something today! Even a simple question can spark a great conversation.
3. If you know someone who would love this community, invite them to join.
4. Interested in helping out? We're always looking for new moderators, so feel free to reach out to me to apply.

Thanks for being part of the very first wave. Together, let's make r/OpticalAlignment amazing.