On Thu, 8 Nov 2001, M. Royer wrote:
> I know that Olympus uses a 'floating mechanism' or a
> 'floating element' to correct for abberations at close
> distance focusing which makes it a must for macro
> lenses. But what exactly are these elements, how do
> they 'float' and how does that help correct close
> focusing?
It's an element (or a group) that sits in a tube inside the lens. As
the focal length of the lens changes, the element moves within the tube.
Think of it as a second internal focusing ring (helicoid) that sits inside
the lens and is connected to the external focusing ring. You can see it on
the 85mm f2 diagram:
http://olympus.dementia.org/Hardware/PDFs/85mm_f2.0.pdf
Look at the rear element, part number CA9805 is the inside of the tube,
CA9816 is the outside of it.
As for why to do it. It basically allows the lens designers to change the
optical construction of the lens (to a certain degree) based on focal length.
-mark
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