On 4/20/2010 7:18 AM, Ken Norton wrote:
> Moose thus grunted:
>
>
>> In 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.
>
Yes, I have a couple of these. the are beautifully built and work well.
The instructions I posted a link to also show the working distances at
various settings with some different lenses.
<http://www.moosemystic.net/Gallery/tech/Lenses/VIV2xMacro/Vivitar_TeleMacro.doc>
> 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.
>
Yup. the advantage of the Viv is that one can vary the extension between
lens and converter continuously, without playing with fixed tubes. I
suppose also that the converter may have a different formula than their
regular ones to optimize it for this use.
I know I have some examples shot with one, but they are hiding at the
moment. ;-) For true macro, it works pretty well, and is handy in the
field, but DOF gets shallow fast. No advantage over a good infinity to
1:1 90-105mm macro, though, other than perhaps some difference in bokeh,
as you say. I've done no comparison
I also have a Panagor macro adapter, which takes a different approach to
the same problem. The adapter is of fixed length and the converter
optics are stronger, i.e. things look smaller when peered at through it
than through the Vivitar. Another beautifully built and finished piece
of equipment.
It doesn't focus to infinity. It starts at 1:10, with interior lenses
closest to the primary lens and moves to 1:1 as you turn the smooth
magnification ring and the optics move toward the camera. this is all
assuming a 50mm primary lens focused at infinity. I don't have
instructions, so I don't know if further close-up using the primary lens
focus is supposed recommended or not.
It's also marked to show the increase in exposure required, from 2.5x to
2.75x, so it is apparently a 2.5x converter. I've never tried it, having
bought it mostly out of curiosity about how it differed from the Vivitar
- quite different designs. Those were film days. Now, I could do a cheap
comparison - but will I?
Moose
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