> ................., I would be interested in what they > consider the optimal dimensions for the pin hole vs. the
> size etc. I will install one tomorrow at my home, > commemorating the Spring Equinox. Here is perhaps a different way of thinking about the problem of the hole diameter vs its distance from the plane on which the spot of light lands. As the hole becomes smaller, physical optics makes the spot of light larger. However, as the hole becomes larger, geometric optics makes the spot of light larger. So I think the thing to do is set the equations for these two diameters equal to each other to find the minimum*. When I do that, I get: D = .03 SQRT L where D = diameter of hole, in mm L = distance from hole to image plane, in mm Since one equation is going up and the other down, the belly of the curve which is their sum is very broad. Therefore, I would increase the .03 figure to .04 to get much more light through with no visible degradation of the fineness of the spot. Reworking the equation, we can see that the angle the spot subtends becomes smaller as L becomes larger. This argues for a large L. On the other hand, the human eye is very good at finding the center of a spot of light, so perhaps I am attacking entirely the wrong problem!! Best, John Bercovitz * I used the diameter of the first dark ring in the diffraction pattern. I used the sodium D line for the wavelength. I used a point object (not the sun, which subtends half a degree); however, what I'm actually trying to do is sharpen the image of the sun, so believe my approach is correct. -
