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Re: [OM] Zuiko 180 lens

Subject: Re: [OM] Zuiko 180 lens
From: "Paul Farrar" <farrar@xxxxxxxxxxxx>
Date: Thu, 2 Jul 1998 13:42:03 -0500 (CDT)
> 
> My direct experience with the Zuiko 180mm lens is null; my remarks are 
> a summarization of those of others from the astrophotographers list.  
> Please take this accordingly.
> 
> The f/2.0 version of the 180 is reported to have outstanding focus of 
> all colors at the film plane and crisp resolution all the way to the 
> corners of the frame.  Therefore, star images, which are always a point 
> source, are round and consistent in color.  On the other hand, the 
> f/2.8 version reportedly does not focus blue wavelengths as preceisely, 
> resulting in a blueish, fuzzy fringe around stars.  This effect is 
> especially pronounced near the outer edges of the frame leading some 
> to speculate this lens also has some coma or other optical abberation.
> 
> This is possibly the result of one bad experience getting distorted out 
> of proportion or is indeed representative of this specific lens.  I do 
> know from experience that a lens that is an outstanding performer in 
> "earth-bound" photography does not necessarily perform well in astro 
> work.  The demands placed on optical and mechanical systems for astro 
> imaging are different, requiring a different set of design compromises 
> for optimal results.  FWIW
> 
> John P

The 180/2.8 is a scaled up version of the 100/2.8 and 135/2.8. As a result
abberations that might be less noticeable at smaller scales may have
gotten scaled up to. I would guess that it was not 3-color corrected, and
as the size was increased, the blue started to get far enough from red and
green that film could resolve it separately. Also as the diameter of the
elements increased, spherical abberation increased. 

Now for astronomers this is a lot more serious defect than it may be for
terrestrial use. It does diminish sharpness and local contrast, but one
has to take the whole package -- flare, ghosts, field-curvature, distortion,
etc. A good astronomical camera is the Schmidt camera, but it wouldn't
be so hot on earth: bad filed curvature (the plates have to be warped),
donut out-of-focus highlights (not a problem with stars), plus the film
is inside the lens. The 180/2.8 seems pretty good on earth to me (an 
owner). And, supposedly, undercorrected spherical abberation gives good
bokeh!

Nonetheless, it is somewhat dated. Ideally, it should be supplemented with
an internal-focusing, apochromatic version. The IF would help on what
I find to be a major shortcoming, the 2m min focus (the 200s are worse,
though). Indoors and for headshots, I just mount it on the 7mm tube from 
the start. That makes it a 1.5m - 5m focusing lens. Olympus does have
an APO-IF 180; it's the too-rich-for-me f/2. If you want a cheaper
alternative (to the f/2), try the Tamron, it's ED IF, and I've heard it's
good.

I don't understand why it costs more than the 300mm.

Paul Farrar

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