...you don't have to focus it (the converter) if it's like the Vivitar
teleconverter I have. Just stick it between the lens and the camera, forget
about autofocus, maybe forget about autoaperture and go take pictures like
real photographers do.
Richard
----- Original Message -----
From: "Chuck Norcutt" <chucknorcutt@xxxxxxxxxxxxxxxx>
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Tuesday, April 20, 2010 11:15 AM
Subject: Re: [OM] Zooms at Dawn - the 50mm shootout - Teaser
> I have a Vivitar 2X macro converter that I've never used. I discovered
> it on the bay about a year or two ago quite by accident and it was going
> for a low price. I guess I should give it a try... if I can focus it.
>
> Chuck Norcutt
>
>
> Ken Norton wrote:
> > Moose thus grunted:
> >
> >> Undoubtedly someone has gone to the trouble of designing an internal
> >> focusing prime with close to constant effective focal length, but it's
> >> got to be tricky and expensive to do. OK, maybe nobody has built one;
I
> >> just want to cover my bases.
> >>
> >
> >
> > Please, somebody, tell me who makes that lens! I'll get one today!
(well,
> > maybe not today, but you get the point).
> >
> >
> >
> > In any case, most of them do change focal length as focused closer. That
> >> was one factor in my choice of the Tamron 90/2.8 macro, which uses a
> >> conventional long helix to focus. The Canon 100/2.8 macro is IF. So as
> >> one focuses closer, the working distance gets even shorter than would
be
> >> expected with conventional design.
> >>
> >
> >
> > Exactly. This is one of those reasons why I've been such a fan of my
lowly
> > 100/2.8 with extension tubes. I get fantastic macro quality as well as
> > serious working distance. Extending the 300/4.5 gives me stupidly long
> > working distances.
> >
> >
> >
> >> With any lens at 1:1, the the focal plane to subject distance is 4x the
> >> focal length. The Canon 100 mm, instead of 400 mm, has a close focus of
> >> 1:1 @ 310mm, for an effective FL of 77 mm.
> >>
> >
> >
> > Moose, I agree with your calculations. However, I am remembering
something
> > that might alter that equation. I hope that somebody on this list has
one to
> > confirm or deny my allegation.
> >
> > Vivitar made a 2X Macro/Teleconverter. This was a brilliant piece of
> > engineering that included an extending section of the tube which moved
the
> > lens farther away from the film-plane which yielded close focusing and
then
> > the 2X optics further magnified the image. If you placed a 50mm lens on
the
> > Vivitar, you could achieve an effective coverage of a 100mm lens, but
the
> > working distance remained about that of a 50mm lens. Also, the bokeh
> > characterists remained that of a 50mm lens--just blown up bigger.
> >
> > It all had to do with the position of the 2X optics themselves. If you
> > placed a normal 2X teleconverter on the back of a 50mm lens and then
> > extended the pair from the film plane, it acts like a 100mm lens in
working
> > distances, etc., but when you extend the 50mm lens first and then
multiply,
> > it acts pretty much like a 50mm lens. Anybody with a 2X and some
extension
> > tubes can easily experiment with this and see for themselves.
> >
> > The reason why I mention all this is because certain modern
> > lenses--especially the 14-54 and 12-60 act like shorter lenses with
> > teleconverters built in. The working distance of the 14-54 in macro is
> > stunningly close. Like REALLY close. As in even at the 54mm setting the
> > lens hood is shading the subject. The 14-54 really does, to MY eye, look
> > like it is being internally extended (focused closer) giving a bit of
> > shorter focal length to begin with, and then multiplied by the second
lens
> > group at the back of the lens.
> >
> > AG (it's all smoke and mirrors) Schnozz
> --
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