Add a camera
Now that we have our hand-ground microscope lens, we can make it more convenient to use by adding a camera. Webcams and cell-phone cameras are inexpensive (the little spy pen camera we will be using here is one we purchased for $8). We will be removing the electronics from the pen, and then removing the lens from the tiny camera, so all we have left is the sensor.
The sensor has 1280 pixels horizontally, and 960 pixels vertically. Here is a closeup photo of the edge of it, as seen through my microscope:
In the photo you can see the red, green, and blue micro-lenses over each pixel, and some of the electrical contacts at the bottom. The pixels are 1.5 microns apart.
I have written a little tool to help design our microscope. It has a picture of our hand-made lens, with rays of light coming from the subject at the bottom of the picture, and you can see how the rays bend as they go through the lens and finally hit the sensor at the top of the picture. Click on the link to see the tool, where you can adjust the sliders to the right to see how things change when you change the distance to the sensor, the wavelength of the light, or the refractive index of the glass or the immersion oil.
Before we get into the construction details, here are some images taken using our little hand-made lens:
Here are some stained paramecia. Note the sharp details, including the nuclei.
Below you can see the image of our stage micrometer, showing the lines that are 10 microns apart:
The disassembly of the spy pen camera is shown in the photo below:
At the top we have the pen in its pristine form. Next we unscrew the pen part, exposing the slot for the microSD card and the USB connector (not seen in the photo). Then, with a pair of pliers, we twist off the gold cap with the pushbutton. It is only press-fit onto the pen top, and comes off with a little bit of force. Lastly, now that the pen tube is open at both ends, we use a pencil to push the electronics module out the top side. It needs a small bit of force, but nothing substantial.
The next step is to unscrew the lens from the camera sensor. This is a bit tricky, since a dab of glue was used to secure it in place after it was screwed into the proper focus position. A crescent wrench was used on the square base of the sensor to prevent the twisting from pulling the whole camera module out of the circuit. Long nosed pliers provided a firm grip on the lens, and after the first quarter turn, it unscrews easiy by hand.
At this point, it is advisable to screw the lens back on, plug a USB cable into the camera, and test it as a webcam on a computer, to verify that we didn't break anything. You can screw the lens in and out to vary the focus. By screwing the lens out almost as far as it will go, we have a useful low power USB microscope already, even before we upgrade the lens to our home-made microscope objective.
It is also possible at this point to simply use a store-bought microscope objective as the lens. A bit of rubber cement will secure the camera to the objective in a non-permanent way, and you can use simple wedges between the objective and the slide to focus your new 5 minute microscope.