AG says:
"It all had to do with the position of the 2X optics themselves. If you
placed a normal 2X teleconverter on the back of a 50mm lens and then
extended the pair from the film plane, it acts like a 100mm lens in
working
distances, etc., but when you extend the 50mm lens first and then
multiply,
it acts pretty much like a 50mm lens. Anybody with a 2X and some
extension
tubes can easily experiment with this and see for themselves."
This is always a tad confusing but some is explained in John Shaw's
first macro book.
I believe the 50mm with a 2X TC directly behind it really only acts as
100mm at infinity.
If one focuses by moving the camera and increase magnification by
extension behind the combo,
then it kinda is a 100mm---though if one uses the lens helicoid it is
not, AFAIK. I think if one uses the Z. 50/3.5 that goes
1:2 and put a TC behind it, the final mag is 1:1with ? same working
distance (need to check) and no where near
that for a true 100mm macro lens. If extra extension is put between
the lens and TC more mag is achieved at the expense of working distance
compared to putting the extra extension behind the TC on the cam.
(Have tried this and the Z,. 50/3.5 does not like TC use)
Moose's comment about the relationship between MFD, FL and mag at 1:1
is quite cool--never seen it expressed that way---clearly is correct
and a really neat thing to know. Thanks!!
Closest I got to the algebra to prove it is 2F=G at 1:1 but g is only
the distance form lens to subject and doesn't include MFD from
focus plane to subject. Too tired to try right now, it is clearly
correct. Must measure with Big Foot at 1:1 as it uses a combo of
standard
extension and floating elements--down side of straight extension is
loss of light of course.
Mike
--
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