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[OM] OM offerings

Subject: [OM] OM offerings
From: Joseph Albert <jalbert@xxxxxxx>
Date: Fri, 25 Sep 1998 23:51:54 -0600 (MDT)
Denton writes:

>We could also use a 200 macro, and a couple other fancy zooms, like Canon
>L, say 17-35. Wouldn't a 17-35 2.8, 35-80 2.8, and a 80-200 2.8 be nice?

nice, but I don't see it as so necessary beyond the 80-200/2.8 sort of
lens and even that isn't so necesary.  a 35-80/2.8 already shoots
at 35mm, so I'd be more inclined to add a 21mm fixed focal to that
than a 17-35 zoom, or maybe an 18mm and 24mm pair.  so that is already
supported.  the canon 17-35 and 20-35 L zooms are very expensive, a little
more prone to flare than the primes, and I doubt they focus as closely.
the wider the lens, the closer it needs to focus since it de-magnifies more
and you have to get closer in to have the foreground subject be large
enough.   I don't think the Canon wide-angle primes are as good as the
Zuikos, so the L wide zoom is a more important part of Canon's lineup.

I'd rather see a 180/3.5 macro that focused by extension and maintained
180mm at all magnifications.  The 200/4 macro's on the market from
Nikon and Pentax are internal focusing lenses.  By focusing internally
instead of by extension, they avoid light loss due to extension, so
there is no bellows factor correction to be applied to the exposure.
This is the good news.  The bad news is that the focal length gets shorter
as the lens focuses closer.  At 1:2, which the 200/4 Micro-Nikkor can
do without extension tubes, the lens is in fact about a 150mm lens only.
It is only a 200mm lens at infinity.  I'm pretty sure a similar situation holds
with the Pentax 200/4 macro, it being an internally focused lens.  But you
don't get the expected working distance of a 200mm lens that focuses by
extension, and certainly nowhere close to double the working distance at 1:2
of a 100mm macro lens.  If this sounds far-fetched (it did to me when I
first read it), you can read all about it in John Shaw's book,
"Close-ups in Nature".

You can add a 1.4x teleconvertor to the 90/2 macro Zuiko and get
a 126/2.8 or a 2x teleconvertor to get a 180/4 that focuses to
1:1 without external tubes and maintains the working distance of
a 180mm lens.

One of the things I like about the Tamron 90/2.5 macro is that Tamron
makes a matched 2x flat field teleconvertor.  It is well corrected
for curvature of field to maintain a macro-quality lens when attaeched
to the Tamron 90/2.5, yielding a good 180/5 that focuses down to 1:1.
Unfortunately, this teleconvertor is adaptall only, no OM or other
mounts available (it goes between the adaptall-2 adapter and the lens.

j. albert

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