Acer said:
>OK, I get it that stars are a point source; no focal length will render
>them anything other than points. But how dow focal length affect how fast
>the trails form? How is the motion magnified when the point isn't?
The whole image is magnified. It's just that the tiny point source of
the star can't be magnified enough because the lens is unable to resolve
the point into a disk. If the image has a diameter of 0 then
multiplying times 10 or 100 will make no difference. The key is not
focal length but diameter which equates to resolving power. It has been
estimated that it would take a 400 inch telescope to image the star with
the largest angular diameter as a disk. I don't know which star has the
largest angular diameter but I'd guess that Betelguese has to be near
the top.
Chuck Norcutt
Woburn, Massachusetts, USA
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