Taking photos and movies with a mobile phone or tablet attached to the foldscape works very well and is great fun. Here I am looking for a cheaper alternative, so that I can let everyone have a go without worrying about the phone. I tried one of these cheap 640×480 pixel webcams with 6 LEDs, which I bought for £4.60 from eBay, here I already removed the little stand (it is not a megapixel camera and has no zoom):
With the lens focused to infinity and the camera as close to the foldscope as possible the result was very disappointing:
The problem is that the actual lens is too far away from the ball lens of the foldscope so that the image fills only a tiny bit of the screen. First I tried to replace the webcam lens with a simple lens, but I found that the original lens design is actually quite clever and consists of several elements:
With the original lens now destroyed, I looked for an alternative and found this one on ebay for £4.80 (3.2mm Focal Length M12xP0.5 Camera Lens for Raspberry):
It can be screwed into the circuit board of the webcam. It is shown here without the casing, you can see the CCD chip, it is only about 1.5 mm x 1.1 mm)
I attached the magnetic stripe with a bit of blue tack and the double sided tape, adjusted so that the hole is centered on the image:
Now I can record movies on the computer e.g. with the quicktime viewer:
Below is a still image with the low magnification foldscope and LED illumination. The object is a stem cross section from limewood (http://www.brunelmicroscopes.co.uk/prepared-slides.html). One problem at the beginning was the saturation of the image, it was mostly white. Putting a piece of paper folded several times between the condenser lens and the stage to attenuate the LED light solved this problem. These cheap webcams also compress the images a lot, which cause artefacts. Anyhow the image is much improved compared to the one at the beginning.
This is an image of the same sample taken with my Lumina 520 mobile phone:
One can see the larger field of view showing more of the sample. The mobile phone has a 3.2 mm x 2.4 mm CCD chip, which is four times the size of the webcam chip. The phone has a focal length of about 2.6 mm, the focal length of the foldscope is 1.7 mm (large lens), which would mean the image is only magnified 1.4x on the CCD chip. In the case of the webcam we have 3.2 mm focal length which results in a little higher magnification of 1.8x. The reason both work so well with the foldscope is because of the small pixel size of the CCDs, 1.2 micrometers for the mobile phone and 2.2 micrometers for the webcam.
When using the original webcam lens (I bought a new one), it is possible to unscrew the lens, so that it is quite far away from the CCD chip. This way it is possible to focus on very close objects. A computer screen is very good for testing. Below is the same sample viewed just with the webcam (no foldscope). The outer ring is about 4.5 mm diameter.
This is the same sample photographed through a simple 2x magnifying glass and with a ruler:
It might have been easier just to cut of the front part of the original lens. Has anyone experience with a better webcam?