Hello everyone,
I’m working on building an OpenFlexure microscope with coherent illumination using a cheap laser module. I disassembled and removed the built-in lens at the tip of the laser module because every imperfection on the lens surface was visible in the illumination.
Now I have a very elliptical beam. To clean this up, I modified the condenser module by adding a 1mm thick layer with a 1mm diameter circular aperture. The hole doesn’t need to be exactly 1mm, as long as it’s adequately circular—which it is!
The problem is the edges of the hole. Any imperfection creates horrible edge effects and artifacts in the illumination. I would really appreciate a clean-edged illumination pattern.
This has been bugging me for a while: How do you make a clean, vertical hole in plastic? I don’t have a drill press—I might buy one, but I’m not sure if drill bits would produce clean edges, and I don’t want to invest before knowing it will work. A heated needle is another option, but it’s tricky to push it vertically into the plastic. Any tilt will likely result in an elliptical aperture.
I checked ready-to-use apertures on AliExpress, but they’re in the micrometer range, which is too small for my application. I also found adjustable camera apertures that cover 0.8mm to a few millimeters. This could work, but integrating it into the condenser module would be challenging.
Has anyone dealt with this problem? What do you use for creating apertures? Or do you prefer to buy them off-the-shelf?
Best,
Berk
Getting a good sharp edge with mechanical methods is very difficult. Most of the prepared apertures are shaped in a thin fool using photolithography and then etching through. 1mm apertures are available to buy from scientific suppliers, but then tend to be quite expensive.
In your case you don’t actually need a hole, you need a clear area. Film photography is really good for that - print out a black circle on white at fairly large size, and photograph it a a distance that makes the circle the size that you want on the film. You will need to be careful with lighting to get the contrast between black and white. Making the black part a hole instead of just printed black will stop reflections making that area lighter. As film photography is less common now this can be a pain to set up and to get right for one aperture, but once you get it, making lots is easy. There used to be high contrast black and white film specifically for this kind of use.
Hey William,
Thank you sincerely for the super, super creative method! Luckily I have a film camera. The only problem is getting the setup right, as I need to optimize for:
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Lighting to get good contrast (good transmission in the hole and absorption/reflection at the opaque section)
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Focus to get the sharpest edges
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Tilt to ensure I get a good circle and not an ellipse
But as you say, once I set it up, I can repeat this many times. I wonder if someone has already done this, but I couldn’t find much on the web. I would happily buy these things if the price was not something crazy.
An alternative is some adjustable apertures I found on AliExpress, around 10 USD each. They look promising, especially if I can modify the condenser part in OpenSCAD. I’m working on that with the help of ChatGPT.
Best,
Berk
I was also thinking over the weekend that 1mm might be large enough for a leather punch to work. Use 0.5mm thick plastic sheet or something rather than leather 
Hello William,
Thank you for the creative idea! I would happily try it, if I can get a leather punch. It’s gives Aliexpress vibes again.
I also had an idea, and I’m curious to see what you think.
It’s easy to drill a hole, but it’s difficult to keep clean edges. What if I printed a condenser piece with a hole, and inserted something circular to this hole with clean edges? And a perfect, cheap solution are these PCB vias (brass rivets) !
Here is how it looks now:
And the edges are much cleaner than what I had with drilling/printing.
I only had a 2.5mm diameter PCB vias at hand. I ordered smaller ones now.
Only problem is, the center of the probe is a bit shiny (also smeared?) in a weird way. It might be due to the reflections: The PCB via is long like 6.5mm, so it’s not a hole, but more like a tube.
I might still getaway with this, if the probe converges during the reconstruction (e.g. as in ptychography with ePIE).
Best,
Berk
A formed hole is a good idea, but with a long tube like that the internal reflections will be a problem for you. You might be able to make it adequately black - copper or brass go black with the wrong treatment, but I don’t know how to do it deliberately!
Your method gives me an idea of different source of thin metal holes - pcb and stripboard tracks. If you take too long to solder a component the track often lifts from the board. You could try doing that deliberately. Stripboard tracks seem to do it more in my experience, or can be removed intact with a sharp knife.
Also, when you run a hot-air station over a small PCB for too long it will completely split the layers, which might make for a slightly stronger thing to use. I have a sacrificial PCB like that, will try it and come back here to update later on in the day
So I tried this and was unable to get it clean off the PCB no matter how much I’d heat it. The resin was bubbling, but the pad stayed in place. I’ll see if I have some stripboard to try instead, but for the PCB I had, I had to take it off with tweezers which then led to it being not-round. Also stuck with black-goo
As for the stripboard - seems to work, but the pads are really delicate and easy to distort. Has to be the green + pads one, I also have a brown prototyping board, but it is copper etched instead? Wasn’t able to get a circle off that pcb this way.
