That isn't an unreasonable amount of extension for a 200 mm lens, but
you won't get the magnification you are expecting me thinks. Longer
focal length lenses require more extension to achieve any given
magnification.
My good book says that image quality will degrade when you push
magnification beyond 1:1 with extension unless you reverse the lens.
Telephotos are not
suitable for reversal.
the classic 50 mm f1.7 reversed with 3 extension tubes is said to
provide
a 1.54 magnification and required an exposure compensation of 6.2 f
stops.
A 28 mm f2.8 reversed with 3 extension tubes is said to provide 3.78
magnification
and require an astounding 19.1 f stops of exposure compensation.
When you talk about image degradation that means different things to
different people. --- With macro photography something will likely
still be in focus and sharp, but the depth of field becomes
progressively less. Shucks if you want to
do super macro photography you can stick your camera on the end of a
microscope
but you have to face reduced depth of field, and reciprocity failure
issues.
when you compensate 19 f stops you have strained the reciprocity
characteristics
of your film unless you have unless you are using a critical mass of
nuclear
fissionable materials at close range as a light source.
Shel Belinkoff wrote:
> Is there any theoretical or practical limit to the length of
> extension tubes? Could a 150mm - 200mm length be used with a
> 200mm macro lens without any image degradtion?
> --
> Shel Belinkoff
> mailto:[EMAIL PROTECTED]
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