It is not possible with current technology, at least at prices we
would/could pay, to design a lens that is acceptably sharp at both 1:40
and 2:1. The conventional Zuiko wide angles are designed for optimum
performance in conventional photography from infinity to about 1:6, and
probably optimum about 1:40. The short focal length macro lenses are
optimized for much different repro ratios, in the case of the 20/2,
4.2:1 through 16:1. Use of just about any conventional lens beyond about
1:2 will give noticeably inferior results.
These are specifically not wide angle lenses (in response to someone
else's question). At the reproduction ratios they are designed for, most
of the field that would be covered by a conventional WA lens would just
end up bouncing around inside the tube(s) or bellows, trying to degrade
contrast. Limiting their angle of view to that required to cover a 35mm
frame at their closest design distance from the film plane makes it
easier to design for optimum performance within their intended repro range.
Your results with the 24/2 on extension tubes is a different thing. The
mirror in SLRs limits the depth of lenses. Wide angle lenses on SLRs
use reverse retro focus designs that place the rear focal node behind
the actual physical lens. Put them on long extensions and you get the
kind of odd seeming results you experienced. Short focal length macro
lenses are never meant to focus anywhere near infinity, so they don't
need special designs to avoid the mirror and their focal points can be
designed to be in front of the physical lens even at very long extensions.
There is very little physical or practical similarity between a 20/2
macro and a 21/2 WA and they are meant to do very different things.
Moose
Daniel J. Mitchell wrote:
So presumably this implies the only reason the macro lenses exist is
because they're physically smaller than the equivalent 'full-size' lenses,
so you can get the film plane close enough to the subject without hitting
it? I've tried using the 24/2 on extension tubes, and I found it wound up
with the in-focus point inside the lens.
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