Does anyone have recommendations for 3D magnifiers for PCB work?

I suspect that because they are designed for a focal distance of 420mm, then if I used them on top of cheap reading glasses I could get much more magnification at a much shorter focal distance.

The focal length of a lens, f, is the distance at which it will focus parallel rays, for example, sunlight.

Given the focal length and distance from the object, O, you can calculate the magnification, M = image size / object size, of the object as shown in the diagram below.

1 / image_distance = 1 / focal_length - 1 / object_distance

Magnification = image_size / object_size = image_distance / object_distance

https://byjus.com/physics/lens-formula/

If you add a second magnifying lens, the combined focal length will be shorter and magnification greater. The focal length of the combination can be calculated by the following formula:

1 / f = 1 / f1 + 1 / f2 - d / (f1 x f2),

where f is the focal length of the combination. The focal lengths of the 2 lenses are f1 and f2, and the distance of separation is d.

https://physics.stackexchange.com/questions/247617/how-is-focal-length-defined-for-a-two-lens-system-separated-by-a-distance-d

I think a lot of the 3-D effect is resolution, and getting a good viewing angle...what if I may ask is the resolution of your viewer?

I know to get to blueray resolution on my computer screen I had to change the video card in my computer, go to HDMI connections, and buy a new hd monitor....even though I thought I had HD to begin with...and change the DVD drive to a blueray capable reader...So getting digital resolution to a 3D like experience is not so easily done...and to get the best experience you need not only high quality optic magnification, but you need high resolution viewing as well...

https://projectorslab.com/everythings-about-resolutions/

The ultimate setup is an engraver type binocular....but can get very pricey

The microscope I prefer for PCB work is the stereoscopic eyepiece-less ones like the Mantis products of Vision Engineering. They cost a pretty penny but IMHO they are worth every pretty penny they cost, particularly if this will be for constant use.

For infrequent, occasional use or you must be more frugal, multiple companies make headband magnifiers.

In the past I spent a lot of time using the older, box-looking Mantis. If I was spending much time at the Mantis I would need to slow down and figure out the best height for my chair and best way to adjust the Mantis arm. Sometimes I would put a board under my ESD pad to raise the work surface by an inch or two. Once you get everything just right you can sit down and be comfortable for hours of 3D magnified work.

(Even a Mantis can not make 0.4mm pitch parts fun to work with.)

For "cheap" have you simply tried the camera on your mobile device?

Used to work in the PCB load/solder/inspect world and there were some pretty good video imaging units that were hand held or able to be mounted.

Most modern phones have camera capability with auto-focus capability. I've also seen aftermarket options for macro lenses to be applied to phones to give that extra capability.

It depends a lot on the resolution required. If your PCBs are using through-hole components on a 0.1" grid, like I've been making for the last 45 years or so, then the OptiVISOR™ headband magnifiers are excellent. Between work, car, and home, I keep 5 sets of them handy, with 2 or 3 magnifications.

Over the years, I've tried quite a few other brands, but never found any quite as good. Definitely make sure the lens/prisms are glass, or at least have ground surfaces. Plastic lens/prisms are commonly molded, although it is certainly possible to make high precision optical lenses (such as the prescription glasses I'm using right now).

Since you mention 420mm focal distance, I suspect that these would do fine. I more commonly use a focal distance between 100 and 200mm.

If you are working with much finer SMC on a much finer grid, then an optical binocular microscope is what you need, but then your focal distance will be way shorter.

Any microscope that has a flat display, by definition does not provide 3D viewing, and in my experience is useless for soldering or other fine work where you need to accurately position your tools.

Have you researched USB microscopes, have used one on a laptop the check SMD device soldering?

Also used them with mechanical adjustment of really small gear mesh after making replacement gears.

A few years back I did some research on microscopes for printed circuit board work. One useful source of information I found were the Louis Rossmann videos on YouTube. Louis and his employee’s use microscopes all day every day. Louis shares his opinions on microscopes. Actually, Louis shares his opinions on many things so you may need a cup of coffee and a few snacks if you are going to watch his videos.

To find several videos go to YouTube and search for “Louis Rossmann microscope”.

Probably the best single microscope video of his is https://www.youtube.com/watch?v=C_eQrbop-J4.

It is also helpful to do YouTube searches on "Louis Rossmann The Tools I Use and Why I Bought Them" and "Louis Rossmann Tools We Use - Tools You Need".

YouTube posted a commercial for the following when I did my search. Now, that is a microscope! https://discover-echo.com/revolution?gclid=CjwKCAiAp8iMBhAqEiwAJb94z1Cd5kE7umdlj_VL_5FF-eKqnfvm3mYGM5Ukadv45N_ArNNh0-g3kxoC3e4QAvD_BwE

WARNING: Louis Rossmann is a New Yorker. He has a computer repair shop on the streets of New York. Louis talks like a New Yorker. Whenever he needs a adjective, adverb or pronoun he uses the same multi purpose, four letter word. I went to school with New Yorkers and I once worked for a Navy Chief. I can handle it. If, by chance, you have tender ears or your feeling are easily hurt then Louis Rossmann’s videos might not be for you.

The digital microscope I have is 1080p, but to get this picture