Thick Lens Focusing Ray Trace This will show the effect of lens aperture on the lens minimum focal spot size at any particular would-be focal plane. The minimum spot size is defined as the minimum region where there is no light rays. When the aperture is stopped down, one effect is there is less light at the would-be focal plane. The other effect is to reduce the spot size at any would-be focal plane. This effect is very noticeable when we try to search for a small object: When we increase the light on the search area, it is much easier to find what we want. Increasing the light causes the diaphragm of our eyes to get smaller and this results in a smaller circle of confusion at our retina. This way, even if our eye lens doesn't focus on the retina, we can still detect small objects. I have elected to provide a checkbox that, when checked, shows the ray opacity due to a circular lens. The ray opacity for a circular lens is greater for rays that hit the circular lens near its outer radius and zero for rays that hit the circular lens center. The apparent opacity is increased when more rays are plotted. As numerical outputs, first I've shown the lens f# which is defined as focal length divided by lens aperture diameter. I also include the calculated thin lens focal length, the position of the mimimum spot size, and the minimum spot size.
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diam rR rL index hAper nRays Cylindrical Lens