The angle doesn't change. But as you wind the focus out, the image size
grows. This gives the effect of reducing the angle. Try it. Put something on
the floor. Sit the camera near it on infinity focus. See the area that the
viewfinder covers. Then rack out the focussing fully (use a macro lens that
focusses by extension). Note the corners of the viewfinder and how they
disappear as you wind out.
This does not apply to internal focussing lenses that I know of. I believe
they internally change their focal length to make it shorter. A previous
subscriber stated that there is no reason why they cannot internally focus
and keep their focal length.
So internal focussing, reduce effective focal length. Extension, increase
effective focal length.
Your kilometrage may vary.
Foxy
----- Original Message -----
> >Why not? The angle covered is still in proportion to the focal
> >length. But at macro distances, the angle reduces significantly. At
> >1:1 it is half the angle ar infinity. So the shutter speed
> >requirement goes up proportionately.
>
> I do not really think that the angle of acceptance changes because of
> the focusing distance. The focal length of the lens does not change
> according to focus distance. Your 90 mm macro lens is twice as far
> away as a 50 mm when you are 1:1.
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