Dr. No Flash states:
"I agree with Wayne. It doesn't matter how the magnification is
achieved,
the inverse square law applies."
Moose
Hmmm.
Sounds quite sure and both Wayne and Moose are smarter than the average
bear.
Looked at John Shaw's second macro book again to confirm and clearly
says that the light
light loss with floating element lenses might be less than with
standard helicoid.
I read a post on Pnet claiming that if one takes a eg. Canon 100mm 2.8
lens with no IF and adds extension to reach 1:2 keeping it at infinity
and use a macro lens of the same type with IF, the IF lens will lose
slighly less light.
Given that N[eff] = N (1+M)---there are no other variables in this, now
I think magnification may be the only relevant factor and the pupilary
magnification is a side issue . Probably the FL of standard helicoid
lenses changes a bit as well as the mag increases.
Seems there are references regarding discussions about this in the past
when it mattered with external metering , but no one cares much anymore
with TTL metering and digital.
There is only one standard helicoid lens here but no clear difference
from the standard bellows factor.
http://www.dpreview.com/lensreviews/panasonic_45_2p8_o20/page3.asp
(look down a bit)
The practical answer is clear. Whether in theory , there is even a
slight inconsequential difference is uncertain. There is at least
some confusion. Error in JS macro book??? gasp.
An Owner of an "I agree with Moose" T-shirt who ignores it at his peril,
Mike
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