=======================
I think the teleconverter should be put between the body and tubes. It is the
way Vivita 2x macro or Kenko 2x macro works.
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actually, the Vivitar 2x Macro convertor has the helicoid that increases
the extension between the lens and convertor, so when extended, it is
like having an extension tube between the lens and convertor.
if you put 2x teleconvertor between the body and tubes, then you are
doubling the focal length, and lose 2 stops of light from the convertor
plus whatever light loss to bellows extension. if the lens is a 100mm lens,
add the convertor, then the tubes behind it, and you need 200mm of extension
to get to 1:1 since the lens + convertor is 200mm. you will lose 4 stops
of light compared to the f-stop setting, 2 from the teleconveter and
2 from bellows factor.
If you put the an extension tube between the convertor and the lens,
the focal length will be somewhere in between 100mm and 200mm, and not
as much light will be lost to bellows factor when shooting at 1:1, but
working distance will be reduced compared to the 100mm lens with
teleconvertor behind it and extension tube behind that. If you have a
total of 50mm of extension behind the 100mm lens that goes to 1:2,
and the 2x tc will go on to 1:1. now light loss to bellows factor is
3 stops (2 stops from TC, and multiplier of 1.5 from bellows factor from
tube). working distance will only be 3/4 as much as the configuration
in the previous paragraph where the TC is mounted directly to the lens,
and extension behind it.
so the tradeoff is working distance vs. light loss. mount the TC directly
to the lens and put extension behind it to maximize working distance at
the cost of light loss; don't use the TC at all to minimize light loss,
but at the expense of working distance; put the extension in between the
lens and TC for a compromise between the previous two extremes in regard
to working distance and light loss, (ie lose more light compared to
no teleconvertor, but less compared to having all the extension behind
the TC, but gain more working distance than having no TC at all, but
less working distance than having all the extension behind the TC).
now with the Olympus bellows mount lenses, I think it is a moot point at
least with the 80/4 in that you couldn't physically mount a TC directly
behind the lens without a tube in between. I assume that the 135/4.5
is the same, but I'm not sure.
joseph
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