George:

Thanks for the response and the link. The Cambridge in Colour Tutorial is one I have visited several times in the past. But, I must admit that, although I read and "kind of" understood the section on diffraction, it obviously was not running through my brain when I pressed the button on the remote.

I learned two important lessons here. The second one is, I should have made several different exposures. I'm sure I'll pass that way again some time in the future. Now, if I can just get it to snow.