Yes,
Eagle eyed Chuck did notice that he Canyon 100/2.8 macro is IF AND
lost a third of a stop MORE light than the only standard
helicoid lens on the list. Not sure how these fallacies get started
and perpetuated and even made it into print (pg 74 JS first macro
book), the equations with non symmetric lenses get quite hairy quite
quickly though. Enjoyed your post summarizing JS's mix and match
TC/extension tube use to either maximize mag or working distance. I am
glad I have 3 of JS's books--still fun to read and overall superb
despite one mistake it appears. I first heard about these books on
this list.
So Moose with vorpal sword in hand and synaptic prowess has slayed two
fallacies in so many weeks. The easier to hand hold shorter FL macro
lens at same mag (my antenna always went up with that one) one (at
least not due to any difference in FL but perhaps lens weight only) and
now this. Bravo.
Mike
It's interesting that the Canon 100/2.8 macro loses 1.3 stops instead
of
1 stop at 1:2. There must be some internal inefficiency that is not
evidenced at 1:1.
John Shaw's explanation for the different working distances and amounts
of light lost in getting to 1:1 with different combinations of tubes
and
teleconverter was that the focal length was not constant. 50mm in one
case, 100mm in another and somewhere in between on yet another
combination. And note that the Canon 100/2.8 macro does internal
focusing and its focal length grows shorter as magnification increases.
Chuck Norcutt
usher99@xxxxxxx wrote:
> 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 first 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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