Winding Demagnetizer Coil

I have added a link to a new article: Winding Demagnetizer Coil.  This describes the construction of a coil for use with my instant demagnetizer.  The secret to good performance is to use a lot of copper, which makes the unit heavy and a bit expensive.

Instant Demagnetizer

I have added a link to a new article  "Instant Demagnetizer." This describes a device I built that allows us to use a withdraw-object-slowly-from-the-coil type of demagnetizer to an instant one that generates a decaying oscillating magnetic field. Just put the object to be demagnetized in the coil and press the button. Done!

Diffraction Blur in Imaging

Because of the wave nature of light, the image of a point is not a point but a blob whose size depends on the wavelength and the f-number of the lens. In the Diffraction Blur article, I compute this blob profile, including  the off-axis case.

Blurring (nonzero blob size) is not caused by the edge of the iris. It is caused by the iris' elimination of the good, far-from-the-axis rays. Larger apertures result in a larger spread in path-length differences for the various rays striking the sensor at points away from the ideal image point. This increases the destructive interference at these points, resulting in a sharper image.

Simple Solution to Monkey and Coconuts Problem

This article describes a simple solution to the well-known monkey and coconuts problem. This is accomplished using base-5 arithmetic.