Re: Sharper Copy Lens for Crown Graphic???????

"stacey" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Nick Zentena wrote:
>
> > stacey <[EMAIL PROTECTED]> wrote:
> >
> >
> >   Xenars don't seem to sell for very much. I've got a
150mm and a 127mm.
> >   The
> > 150mm wasn't very much and the 127mm came free with a
camera.  Best thing
> > about the 127mm was the 0 shutter that I was able to
screw a 150mm Claron
> > right into. My 150mm is just fine if a person didn't
want a lot of
> > movement.
> >
> >
>
> It's weird, almost every xenar I've used works great
except that 135mm f4.7.
> The 75mm one on the rolleicord is a really good performer
and I have a 35mm
> folder than has a 50 f3.5 that is sharp as a tack. Not
sure what the deal
> with the 135mm one is but it seems to be a dog for some
reason..
> -- 
>
>   Stacey

  For some reason the 127mm, f/4.7 Xenar has excessive coma
very similar to the Wollensak Raptar/Optar. If you look at a
small highlight near a corner at full aperture you will see
its smeared out roughly in a teardrop shape. As you stop
down the smearing becomes less. All Tessars have some coma
when wide open but for the 135mm, f/4.5 Zeiss Tessar or
127mm, f/4.7 Ektar, the coma is gone at f/8 and the corners
are quite sharp at f/11. Both the Xenar and Raptar/Optar
must be stopped down nearly all the way to eliminate the
coma. Both Xenar and Raptar are quite sharp in the center
when wide open. I suspect a design problem rather than a
manufacturing error. I wonder how both designs got to be so
wrong.
  Other Xenars do not suffer from this fault. The two I have
in Rollei cameras have little coma and are very sharp. I
have other Wollensak lenses which are very good but somehow
the lenses for the Speed Graphic and Wollensak Enlarging
Raptars have real problems.

-- 
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Richard Knoppow
Los Angeles, CA, USA
[EMAIL PROTECTED]