brass – In the time of visas

In Leiden I stumbled across a Antonie van Leeuwenhoek microscope[1]. If your early microbiology and microscopy is a bit rusty, I would highly encourage you to go on an all night research binge – it is exciting stuff! Also, when near Leiden, visit Museum Boerhaave. For science!

Simple Van Leeuwenhoek microscope, Museum Boerhaave

I wanted that microscope. Not just to have, but to make one. To get close to the materials, to better understand the process. Also, after a few years of consistently thinking about abstract algorithms, making something physical was extremely appealing. And the proximity to great science was appealing: I can now say that, just like Robert Hooke, I recreated a very satisfying little microscope.

The microscope uses a glass bead as lens; this is housed in a brass body, with adjustment screws for adjusting the focus an object position. I largely follow the instructions here [2], which was particularly useful for the lens making process. I’m new to both glass and brass, which made this extra fun.

I tried a number of glass sources, but ISO standard pesto jars performed very well. You need a fairly low melting temperature, and limited stress in the glass. I used drawing to make the lenses, apparently grinding and blowing are also options[3]. For someone with limited tools and glass experience, I highly recommend drawing. A fairly hot flame is required, but it needn’t be huge. An alcohol burner failed, but a cheap pencil torch worked for me. More heat will give you larger beads, with a better (longer) focal distance, but they also have more imperfections and lower magnification.

Wear eye protection.

To make the beads, melt the tips of two shards in the flame, then smoosh them together to form a glob of glowing glass. Based on colour, I would estimate it to be around 700-800’C. Remove the ball from the flame, the gently draw the two shards apart. A thin glass fibre should form, with the thickness determined by the temperature of the glass and speed of drawing. Collect several fibres.

To make the lenses, you melt the tips of the fibres in a hot flame, one at a time. As the strand melts, the surface tension pulls the molten glass into a little ball. This little sphere will act as a high magnification lens. Gently rolling the fibre between your fingers encourages even heat distribution, and better bead formation. As the ball grows, the glass fibre bends down, pulling more of it into the flame. At some point the fibre will burn through, resulting in an upper limit of the size of bead. My 2 – 3 mm diameter beads came out best – very round, clear, with limited imperfections.

Lens beads – the large one wasn’t amazing, but the small ones did quite well.

Dimension were collected from a number of sites, but I mostly stuck to those here[2]. The body sheets are cut from a 0.5mm brass sheet. The lens cavity is made by squeezing a sacrificial lens bead between the body sheets, and gently beating them together between two bits of wood. This process bends out the sheet around the part where the lens will be. Due to the short focal distance of the lenses, one also needs to grind down the excess brass that the lens displaced – all you need is a thin lip to keep the final lens in place. Once everything looks nice and solid, insert the bead you’d like to use as lens, then rivet the two sheets together to keep everything snug and stable. I used more of the 2mm rod for the rivets.

Test fitting the lens.

The L-bracket is cut from 1mm stock. The focus block is about 5mm thick. I tapped 2mm holes in where directed. For the screws, I used a die to cut thread into a 2mm rod. This can take a while. A bit of hammering gave wings of the screws.

All the little bits. The body is about 50mm x 25mm, screws were all cut from 2mm rod.

The focus assembly. The long rod rotates freely in the focus block, while the threaded hole in the L-bracket determines vertical displacement.

Then assemble. A sharpened screw acts as holder for the object of inspection. If you can’t impale the object of your curiosity, wax or (in my case) a dab of glue helps to keep the object in place.

Hold the microscope close to your eye, against the light – blue sky is good, some people use the sun. Then twiddle and twist screws to get everything into focus. The long rod controls the up-down displacement of the object, while the short screw in the image above pushes the focus block away from the body sheet, lifting the object with it. The L-bracket can rotate, which gives a combined left-right and up down movement.