Lex writes:
<< Ahh, interesting. I've been puzzled about what's appropriate when
using
other-than-macro lenses with various close up devices (close up diopter
lenses, extension tubes, Vivitar's macro focusing 2x teleconverter).
For
example, is it considered best to leave a normal lens focused at
infinity
for best results and move the camera or subject to within focus range?
Or
is it okay to use the lens' focus mechanism to get maximum magnification
when combined with diopters, extension tubes, etc.? I've never read a
definitive answer on this. My own informal tests of 2D objects doesn't
reveal any particular difference, but I may be less critical than some.
>>
Unless the lens has floating elements or internal focusing, it would
make no difference if the extension was made via the internal helical or
by external extension tubes. But the 21mm f/2, 24mm f/2, 50mm f/2, 50mm
f/3.5, 85mm f/2, 90mm f/2, 100mm f/2, 180mm f/2, 250mm f/2 and 350mm f/2
Zuikos primes should all be extended out to and left at maximum helical
extension before using extension tubes. I don't know about the zooms.
<< That reminds me ... with a lens like Vivitar's old 90mm f/2.8 macro
(the
non-Series 1 version) that goes 1:1 without an extension tube - does
this
type of design inherently involve either a loss of effective focal
length,
effective aperture, or both as it's extended to maximum magnification?
Again, I haven't been able to find a definitive answer anywhere. >>
It looses light transmittance as you focus closer, with significant loss
beginning at about 1:5, due to "bellows effect." That loss is lessened
in a floating element or internal focus design if it decreases in focal
length as you focus closer. The 50mm f/2 Macro Zuiko is such an
example: it decreases to 40mm at 1:2 magnification.
Gary Reese
Las Vegas, NV
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