Acer Victoria <siddim01@xxxxxxxxxxxxxxx> wrote:
> >>>With a fixed 50mm lens, at mid-latitudes, stars will begin
> to trail in about 20 seconds, with a 35mm lens, trailing begins in about
> 30 seconds.<<<
>
> Come again? Since the 35 is wider, why doesn't it trail earlier? I mean,
> [...]
Shorter focal length => less magnification of star motion => less trailing.
Same reason it's harder to handhold long focal length zooms than a short
wide-angle, except the motion's in the subject not the camera.
Stars farther from the earth's polar axis will trail more quickly, I'd
imagine, but I'd guess that's why the numbers are only approximate...
:-) My quick calculation suggests that the FOV difference between a
(OM content!) Zuiko 50mm/1.4 and a Zuiko 35mm/2.8 is not enough to
outweigh the magnification effect in terms of image velocity across the
film. But I might be wrong: it's 2am. :-)
joey
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