To get the magnification, just divide the focal length of the
lens by the extension added. This is of course assuming
that you are focused to infinity. That means that a 50mm
lens requires 50mm of extension to reach 1:1 (remember
that the lens is focused to infinity) The 50mm lens I read
racks in and out about 7mm. So, it you are focusing the
lens down to its closest focusing, it is an automatic 7mm
of extension. So, your results were close:
> 13 + 21 + 31 : 1,24x <-> 1,40x
The actual magnification is as follows:
(13+21+31)/50 = 1.3 (focused to infinity)
(7+13+21+31)/50 = 1.44 (focused to minimum close)
Hope that helps out!
-Chris Riek
> -----Original Message-----
> From: Olaf Greve [SMTP:Ogreve@xxxxxxx]
> Sent: Wednesday, June 16, 1999 7:33 AM
> To: 'olympus@xxxxxxxxxxxxxxx'
> Subject: [OM] Extension rings magnification tables (long)
>
> Hi,
>
> Yesterday I came across a set of three Hama auto extension tubes and since
> the set only cost $20 I bought them, so yesterday was my first experience
> with extension rings and I was quite impressed at the magnification level
> they allow with the 50/1.8 lens (I haven't really tested them with other
> lenses yet).
>
> I asked Hans for a table of magnifications and he recommended me to focus
> on
> a ruler and then use these measurements (in relation to the 36x24mm
> framesize) to determine the magnification level.
>
> To do this pretty accurately, I mounted the rings on my OM-40 (as I didn't
> adapt the screwmounts yet so the rings can safely be used on the 4Ti
> without
> shearing off the reset button) on a tripod and vertically clipped a ruler
> on
> a bookstand. Then for each combination of rings I first moved the focusing
> ring of the lens all the way to the min. focusing distance, and then moved
> the bookstand (to and away from the camera) until the ruler was focused
> properly (because of the incredible small d.o.f. this wasn't a
> straightforward task at times), then I carefully moved the ruler
> (vertically) so that the 0 cm mark was aligned with the top of the frame
> (the viewfinder frame, that is), and then I wrote down whatever amount of
> milimeters the bottom of the frame was aligned with. Then I performed the
> same procedure with the lens' focusing ring turned all the way to the max.
> focusing distance (i.e. "infinity"). By doing this I obtained the
> following
> table of ranges (expressed in mm.):
>
<SNIP>
>
> Hmmmm, I just checked these numbers against the table that appears on
> Hans'
> e-sif page and it turns out that the left side numbers (i.e. focused at
> "infinity") are pretty accurate, but the min. distance focusing numbers
> are
> quite off. It seems that the min. focusing distance multiplication factor
> would actually be something like 0,023...
>
> Oh well, this should probably be attributed to inaccurate measuring on my
> side, although I thought the measurements were quite accurate...
>
> Either way, the magnification range is pretty impressive, almost the
> complete range between 0.25x and 1.40x lifesize is covered by something as
> cheap as three off-brand extension rings and a regular 50/1.8 Zuiko!
>
> Hope this is of use to anyone...
>
> Cheers!
> Olaf
>
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