Re: EOS EF 20-35 with extension tubes

[Bob Talbot]

> Magnification on the 20mm is 0.14 and it's 0.13 on the 20-35... How
can
> this be with such a difference in closest focusing distance.


The close-focus is a function of focal length AND inherent bellows
extension.
Why is actually a very  interesting question.  I'm wondering if it is
akin to the *so-called" doublers.  They don't actually double the
focal length they just magnify the centre of the image circle giving
an image on film the size that would ....

Thinking aloud ... maybe the reason the 20-35 can't be made to focus
as close as the 20 is that the latter is a 20mm and the second a 35mm
front end  being made to behave as a 20 by jiggery-pokery.  Were that
true the minimum focussing distance would certainly be limited by
physics not design ....

I'm intrigued to know if anyone has hard facts on this.

Bob

*
****
*******
***********************************************************
*  For list instructions, including unsubscribe, see:
*    http://www.a1.nl/phomepag/markerink/eos_list.htm
***********************************************************