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Re: [OM] HELP ! Zuiko Lenses, reversing for Macro, and Digital ...

Subject: Re: [OM] HELP ! Zuiko Lenses, reversing for Macro, and Digital ...
From: "Carlos J. Santisteban Salinas" <cjss@xxxxxxxxxxxxx>
Date: Thu, 5 Dec 2002 21:39:19 +0100
Hi, everyone.

> It's a N*k*n Coolp*x 5700.  On it he has
> some sort of arrangement (looks like it just slides over the lens ?) to hold
> any filters he wishes to attach.
>
> Now comes the tricky part.  He has learned that Zuiko lenses are
> particularly good for Macro stuff, and has expressed an interest in
> obtaining a 50/1.8 and fitting it backwards onto the filter ring of this
> camera.  Apparently this should work (any comments ?).

This seems to be the so-called "afocal setup". In fact, the 50/1.8 is
acting like an achromatic, aplanatic, acomatic (?), anastigmatic,
flat-field, orthoscopic close-up lens. In other words, a super-duper
magnifying glass -- that's what junky 50/1.8s are for, as we all already
know ;-)

>Zuiko excels in TRUE macro lenses. A 50/1.8 even reversed is not a true macro
>lens. And if that is how your friend wishes to use it a Zuiko will not be
>much different from a Canon, Nikon, Pentax or the likes.

I agree, any 50/1.8 will do the job. But the afocal setup makes the
reversed lens work like at "infinity" focusing, so a *true* macro, like the
Zuiko 80mm F4, will perform *poorly* in this particular setup.

However, I think a Zuiko is the best for this task because:

a) It's compact and lightweight

b) The flange-to-film (flange-to-subject, when reversed) distance is
somewhat larger than most other SLRs, which means a bit more of working
distance.

c) The lens keeps always wide-open when reversed -- a hassle with a
bellows, but needed for the afocal method.

d) Last, but not least, IT'S A ZUIKO :-)

>Secondly, simply reversing the lens is not likely to do much good. Non macro
>lenses are optimized for use where the distance between the lens and film
>is much smaller than that between the lens and subject.

Yes, that's the problem when reversing a standard lens on a bellows -- an
extreme extension is needed for optimum performance. But the afocal method
is fine for moderately high reproduction ratios: the reversed lens takes
the subject where the film should be normally, and renders the image at
infinity (where the subject usually goes) -- the scheme is reversed as the
lens is, so everything's OK. Then, the main (fixed) lens on the (digital)
camera won't have any problem to take the rendered image at infinity, as
usual.

To avoid light loss, the entrance pupil (the aperture) of the reversed lens
should be larger than that of the main lens. Digicam lenses are usually
small, so that won't be a problem. BTW, the total magnification is: (main
focal length)/(reversed focal length). This won't give a high magnification
with a digicam, but due to the small size of the CCD, if would allow
extreme close-ups!

Hope this helps,

...

Carlos J. Santisteban

<cjss@xxxxxxxxxxxxx>
<http://cjss.galeon.com>



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