We want to find lenses that meet our resolution limit requirements and our working distance requirements. To get a working distance of about 10mm, we want a lens with a focal length of about 10mm. With cost restrictions in mind, we found two BK7 lenses, 12.7mm in diameter and 12.7mm in focal length, from Newport Optics. These lenses meet our price requirements, as they are $20 each, and we will continue on to show that they meet our resolution requirements.

Raleigh Criterion

Final Decisions

In the end, we had to trade off some resolution in order to have an achievable mechanical design. For instance, we decided not to have adjustable magnification because it required complicated changes in the distances between the objective lens, the eyepiece lens, and the CCD. For the same reasons, the focus is only adjustable by changing the working distance.

Trial and error testing showed us that, even using an optical bench, the precision necessary for high resolution, focus, and magnification was incredibly difficult to achieve. Thus, we ended up using 20x magnification for our microscope, and this allowed us to resolve on the 20-30 micron level.

With this magnification, we were able to take a picture of LCD pixels on a notebook computer screen. The pixels are about 230 microns across, and each subpixel (red, green, and blue) is about 60 microns. Here is a picture of a pixel.

Note that these pixels are not perfectly rectangular, and that each subpixel is notched in two corners. In our own picture seen below, we can see the notch that sticks out of the green pixel. This notch should be about 20-30 microns large.