jrk_om@xxxxxxxxxxx wrote:
>The macro focusing Vivitar 2x teleconverter has a built in "adjustable
>extension tube" allowing it to give your lens even closer focusing. I
>believe the macro focusing 2x is a 7 element design while the 2X-21 is a
>four element design.
>
Virtually all third party tele-converters are either 4 or 7 element
designs. The 4s are pretty rough , but not too bad in the center. My
impression is that all the 7s, except possible the Tamrons non-adaptall
ones (Adaptall ones are certainly different), are just different names
on the same lens from the same factory. They are certainly better than
the 4s.
>I read on another group that the Vivitar match mate teleconverters were 7
>element designs made by Kiron. I've never seen one first hand so can only
>raise this as something to look into. The Vivitar lenses that are made by
>Kiron have serial nos. beginning with 22.
>
>Most of the teleconverters are designed to work with long focal lengths. If
>you try to use it with lenses shorter than about 85mm you may get
>vignetting.
>
Not true of all of them. A Rokunar 7 element doesn't vignette with a
50/1.8. Certainly true of the Kiron 1.5x, which is designed for 75-150mm
>The few shots I've seen using the Vivitar macro focusing
>teleconverter didn't show any problem. They were taken at macro distances
>though so they would be less likely to show a problem.
>
The Vivitar M-FT specs say it is suitable for lenses from 28-400mm. It
is obviously designed primarily for 50mm lenses, as the variable
extension maxes at just the length that brings a typical 50mm lens to
1:1 repro ratio and the barrel is marked with repro ratios for 50mm
lenses. With longer lenses, it has a smaller percentage effect on close
focus, as its maximum extension is a smaller proportion of the focal
length, but still makes a significant improvement in CF. I really like
it. It both turns the 50/1.4 into a 100/2.8 macro that focuses to 1:1
and works as a quality doubler for long lenses, making it a small
multi-tasker in a small kit. I'm sure it is not in the league of a true
macro lens with extension(s) in flatness of field or resolution, but its
pretty damn good down to and at least somewhat past 1:2.
By (buy?) the way, I got a little over enthusiastic about these and have
an extra for sale.
Moose
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