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Re: [Rollei] OT: Crown Graphic recommendation



- ----- Original Message -----
From: "Paul Kollas" <pkkollas  >
To: <rollei  
Sent: Tuesday, November 05, 2002 11:24 AM
Subject: Re: [Rollei] OT: Crown Graphic recommendation


> I have an old uncoated Ektar 127, a Xenar 135, and a
Linhof Xenar 150.
> I don't do portraits, and I've never made any critical
tests or
> comparative analysis of the results of these 3.  So I'm
essentially
> useless to you, EXCEPT that I have always been impressed
with the
> Ektar's sharpness, and gut-feel that it isn't back-seat to
any other
> Tessar type lens.
> Just to add to my already frivolous information, I also
use a Bausch
> and Lomb Wide Angle 88mm f/6.8 (uncoated), and a 7" Goerz
Dagor f/6.8
> (uncoated).  The Ektar goes on my Anniversary Speed, along
with (at
> separate times) a Schneider Componon f/5.6 150mm.  The
others are for
> my Pacemaker Crown.
>
> pk
>
> On Monday, November 4, 2002, at 06:58  AM, Jonathan
Prescott wrote:
>
> > A couple of more specific questions: How does the Ektar
stack up
> > against the Xenar? Does a Graphic have enough extension
to use a
> > portrait lens in the 210 range?
> >
> >
> >
> > Jonathan
>
   I have both coated and uncoated 127mm Ektars. They are
extremely sharp lenses with excellent color correction. The
uncoated version has a slight ghost image of very bright
objects. You will see it if you point the camera at a
lightbulb but it probably has no effect on average
photographs. The ghost image is not present in the coated
version.
  Ektars, and many other older lenses, tend to become hazy
inside. The haze ruins the contrast but is easily removed.
The front cell of the 127mm lens can be opened with a
friction tool. The front retaining ring is threaded in. The
friction tool is a tube the right diameter with sticky
rubber around its periphery. Sometimes the paint around the
threads must be removed.
  152mm Ektars have threaded back caps which can be removed
by hand. The haze cleans off with any lens cleaner.
  Ektar lenses were intended to boost color film sales. They
are completely corrected for lateral color and have very
little longitudinal color.
  I don't have an equivalent Xenar but remember a couple I
checked some time ago had more coma than the Ektar, meaning
they had to be stopped down more to be sharp in the corners.
  The Wollensak Raptar/Optar is very sharp in the center but
has excessive coma and must be used at f/22 or smaller to be
sharp in the corners, the Ektar will do it at f/11. FWIW,
the older f/4.5 Zeiss Tessars, once the standard lens on
Speed Graphics, is nearly as good as the Ektar. It has a bit
of spherical wide open but is sharp all over at f/11. The
Tessar has no ghost image but the Ektar is just a bit
sharper and probably better color corrected.
  The required bellows draw is:

v = Fu/u-F  where

v = Image distance
F = Focal length
u = Subject distance

Subject distance = u = Fv/v-F

Note that these distances are measured from the principle
points of the lens. For normal (not telephoto or retrofocus)
lenses they can be measured from the center of the lens.


  The extension from the infinity focus position is:

x' = F^2/u-F  where x' is the extension.

 For a 210mm lens and a 12" bellows the minimum distance is
27 inches.

  Since magnification = m = v/u the image size will be a
little less than half the object size.

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