I made a Leeuwenhoek homage microscope, and thought some of you might be interested.
My goal was not to create a strict replica. Instead, it's an interpretation of one with a few modern twists. I did want it to remain recognizable - to those in the know - as descended from his classic pattern.
Leeuwenhoek's advantage, back in the day, was his ability to make a "simple" (single-lens) microscope with high power and quality. Before the advent of achromatic lenses, compound microscopes suffered from severe aberrations, and a finely-made single-lens microscope could be superior.
Rather than grind my own lens, I simply bought one. It's a single-coated, two-element achromatic lens, 3mm in diameter, 3mm thick, with a 4.5mm focal length and a numerical aperture of 0.3. This is 222 diopters, or roughly 55x magnification, and is in the neighborhood of Leeuwenhoek's lower-power surviving microscopes.
You can see reflected light in the dividing line between the "crown" and "flint" glasses. Of course, using an achromatic lens provides an unfair advantage over Leeuwenhoek's microscopes, but if he could have used one, he certainly would have!
Leeuwenhoek sandwiched his lenses between two thin metal plates, which were subsequently riveted together. This technique "stopped down" his lenses, providing some benefit in reducing aberrations from the lens periphery (he likely understood this).
My lens, though, could be expected to provide high quality imaging virtually edge-to-edge. Therefore, I used a solid brass plate with a reamed and counter-sunk hole to accept the lens. This leaves the entire lens free for use, e.g. for a more comfortable and wider field of view.
Here's a picture of the Leeuwenhoek-shaped body of the microscope with the lens sitting on top:
My next step was to decide on the focusing mechanism. Leeuwenhoek's design used a screw on the back of the microscope's body that forcibly pried apart the whole mechanism to change the lens-to-subject distance. It also would slightly move and twist the subject in the process. I wanted to avoid the prying action in my microscope, partly on principle, but mostly because I was using essentially unbendable solid metal construction.
His microscopes also had a screw (the "handle") that adjusted the vertical position of the subject, as well as a cruder way to adjust the position of the subject horizontally. I decided to reconfigure his controls and use the "handle" screw to adjust the focus. Since this was made just for fun and not for (much) actual use, I was not very concerned about vertical and horizontal repositioning.
I happened to have a small micrometer head on hand, so I used that for the "handle" screw rather than a threaded rod. Here it is mounted to the body:
Next I had to decide on how to hold the subject, and how to focus it. In all surviving microscopes, Leeuwenhoek used a point to hold the subject. I preferred to implement some sort of glass slide.
I mocked up a stage and focusing mechanism in 3D printed plastic to try it out. My idea was to insert small round "slides" into the stage's hole. Here's the stage's mock-up, clamped to the body. The screw pushes on the stage, deflecting it and therefore changing the focus point:
After that, it was time to cut metal again. Because the metal would have to bend a little, I used springier phosphor bronze instead of brass for the stage. The knob on which the micrometer pushes is in brass still:
And here it is with two "slides." These are 3D printed plastic carriers into which 10mm glass windows are placed. The two slides shown have different depths at which the glass is held, allowing some coarse adjustment of the focusing point if needed. The one in the stage is deeper (closer to the lens) than the one to the side:
And finally, here's the completed microscope. The lens is a bit hard to see because of its anti-reflective coating, but it's there:
It works very well, and the image is nice and sharp! With the N.A. of 0.3, the field of view is quite decent, and you can "look around" the field a bit. Although you have to hold it extremely close to your eye, this does not turn out to be too difficult, and in the end it's comfortable and easy to use.
I used it to image a smear of my own blood, and the red blood cells are very sharp and distinct, with a pale straw-red color. At about 55x, you can imagine that they have a certain shape, but it's hard to be sure.
The main difficulty, I've found, is providing suitable lighting. Flat illumination from behind results in low contrast. An oblique source is much better. Indeed, it's presumed that Leeuwenhoek must have used oblique illumination to have seen some of what he reported.
It was a fun little project, and I learned a lot in the process!
Thanks for reading.
