Re: [OM] Birds, Bokeh, and DZes

[Ken Norton]

I'm reminded of a lesson learned with the Vivitar 2X macro extender. This
device sat between the lens and the camera body and not only provided
variable extension but included the 2X multiplier optics.  The rule of thumb
is this:

The multiplier sitting behind the extension provides magnification of the
image being transmitted through it.  However, if the multiplier is sitting
in front of the extension, the image will have the characteristic of the
multiplied focal length of the lens used. The resulting images are
completely different.

Inotherwords, if you placed a 2X multiplier behind a 50mm lens, you
generally got a similar image to that from a 100mm lens.  And then you just
extend this lens-combination to get the close-focusing you want. However, if
you place the extension between the 50mm lens and the multiplier, you got
the image characteristics of a cropped 50mm lens image. This had a
tremendous bearing on the resulting bokeh.

I suspect that many lens designs today (especially zooms) are essentially a
short focal-length followed by a multiplier (or variable multiplier in the
case of zooms).  Since most lenses now are IF (internal focusing), the gap
between the front group and the back group is being extended during
focusing.  This would explain why many zoom lenses give the image results of
a crop of a lesser focal length instead of the bokeh of a fixed prime lens
of say a classic Tessar design.

AG

You want beautiful bokeh?  Get yourself a classic Zuiko 35/2.8.
-- 
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