From: "Lex Jenkins
> Frieder Faig offers helpfully:
> >Easy to find out. For 1:1 magnification a lens mus be elongated for it`s
> >focal length. Take a ruler and meassure the lenght of the lens when
> >focused to 1:1-magnification, and subtract the lenght when focused to
> >infinity. If it matches the focal length, it loses 2-f-Stops. If it is
the
> >same (IF-lens), it loses half of effective focal lengh. If it is in
> >between, It losses an (smaller) amount of both.<
>
> Ah, OK, I got it. I think.
>
> Mmm... could you repeat part of that... the part starting with "Easy to
find
> out."
>
> Lex ;)
Try this idea. When the lens is further from the film, the area the image
covers is greater i.e. at twice the distance the area is four times as big.
Four times as big means each area gets 1/4 as much light. One stop change
allows 1/2 as much light, so 1/2 X 1/2 or two stops means 1/4 as much light.
Compensate by opening up two stops. Clear as mud?
Gregg
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