Hi, Gary,
The extender will have no effect on closest focusing distance, so it will increase magnification.[a href=\"index.php?act=findpost&pid=66663\"][{POST_SNAPBACK}][/a]
Indeed, the extender doesn't effect the closest focsuing distance as measured from the first principal point of the lens, which is the distance that affects the maximum magnfication of the main lens itself.
That magnfication is then "multiplied" by the multiplication of the extender. (That is essentially how the extender multiplies the focal length!)
Adding the extender does change the closest focsuing distance as measured from the focal plane (which is how focusing distances are usually stated), just because it moves the main lens physically outward by the "length" of the extender (and thus moves out the first principal point, which remains in the same place in the main lens).
Please excuse my introduction of the term "main lens". The tradiitional technical term for that is "prime lens". but of course that term has in modern times been hijacked to mean "a lens of fixed nominal focal length"!
It shouldn't be surprising that the minimum focusing distance of the two lenses cited would be different, since they have different optical desgns. (It is not as if the IS feature were something "bolted on" the outside of the lens.)
