On Tue, Jan 16, 2001 at 08:52:54PM +1100, Terry and Tracey wrote:
> 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.
IMHO, does the angle change, when you reduce the angle?
It seems strange but it is so, that the angle change when you thouth out
a convetional lens.
Have a look at a Olympus lens overview. Compare the angle of view
of the 2/21mm with the angle of view of the Zuko Macro 20mm/F2.
92° vs. 9°(at highest magnification). Well, when ou use the 2/21 on the
Bellows, the angle is just the same.
To realize this, it is good to accept the meaning of the sentence, it is the
apperture which makes/renders the picture. First I heard this I thought it
is stupid, out-of-date old fashined photograpic knowlede.
But it means, it is the distance of the apperture, which determines the angle
of field. (The focal lenght is just rlevant, of what is in focus at this
distance.)
>
> 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.
Now this depends on your point of view, how you define focal lenght.
Frieder Faig
>
> 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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