How to, Photograph/Track the Stars... Cheaply.
Ok... I confess I have not built one of these. But stumbled across these sites a few weeks ago, and thought someone may be interested... never know...
How does the Scotch mount work? Let's begin by considering two facts. First, the Earth turns 360 degrees in 24 hours. That translates to 15 degrees per hour, or 5 degrees every 20 minutes. Next, one of the most common pieces of hardware is the 1/4-20 screw (1/4- inch in diameter, with 20 threads per inch). If this screw is turned at a rate of one revolution per minute (one RPM), then it will travel one inch in 20 minutes. Putting both of these facts together creates what I call the "20-minute Triangle.” Using a little trigonometry, it turns out that if a 1/4-20 screw is placed exactly 11.42 inches from a pivot (e.g., a hinge) located at "A" and turned at one rpm, the triangle's hypotenuse will move at approximately the same rate as the sky. Anything mounted on the hypotenuse (such as a camera) will move right along with the stars.
Now... LOL... I've saved the 2 links/pages above as PDF for future reference/use...
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