High on the list of world changing, Nobel prize winning inventions that nobody has heard of is the phase contrast microscope. This microscope uses some tricks that exploit changes in refractive index within a sample, allowing you to see details of cells that you generally can’t see without staining. The problem with staining cells is that it kills whatever you apply it to. Phase contrast microscopy made it possible to observe processes in living cells and improved our understanding of cell biology. In general, a phase contrast microscope gives you a much better image if you just want to look at really small biological things.
I recently got given a Leitz inverted microscope. Leitz is an old german company that has become Leica microsystems – those guys that make really expensive microscopes. The microscope was in very good condition, a bit of dust and a couple of missing parts.
Here’s a diagram with the missing bits (if you want to know the working principles, try wikipedia). It seems that to get it working I’ll need a new lamp, a phase plate (phase annulus) and to give it a bit of a spruce up.
A New Lamp
I decided I didn’t want to modify anything, and that I would use an LED instead. The LED would need to be positioned in the same place as the original lamp would be, and at this point I was unsure about how critical the position would be. To this end I began making an aluminium insert and a few other parts that would allow me to position the LED in 3D space with what turns out to be unnecessarily high precision.
Some turning on the lathe gave the basic shapes, an insert for the original lamp housing, a retaining ring that fixes the vertical position while the horizontal screws are being adjusted, and a bar with a rough heat-sink for mounting a high power LED.
Next, to the mill to cut some flats for the adjustment screws, a channel for wires, and make some threaded holes for screws.
Just need to do some soldering and glue the LED and wires in place, and we have light…
Phase Contrast Annulus
To get it doing phase contrast I’ll need a phase contrast annulus. I thought about 3D printing one, but I thought I’d see if I could find an original. After all, the lamp gets quite warm, and I had no idea what the correct dimensions were supposed to be.
After digging through the manual and blog posts I eventually worked out that I needed a “Phaco 1 Annulus” and it seems there was exactly one in the whole world for sale, Midwest Microscopes – located in the US, presumably somewhere in the midwest. The guy was very friendly and shipped it within a week.
Shiny.
And… it works
This is a picture I took through the eyepiece of some olive oil as a test. Turns out that even though it looks pretty clear, it’s full of tiny precipitates – it was pretty old oil.
Finishing Touches
I cleaned all the optics and there was one final thing to do. It originally came in a big plastic bag which only just fitted on. It was a pain to take on and off, and looked awful.
So, I decided to use the spaces sewing kit to make a proper cover. With Josh’s assistance we got a nice faux-leather cover made.
All looking good on the bench, ready to use!
