[LargeFormat] Process lenses... which one should I get?

[Richard Knoppow]

----- Original Message -----
From: "Jim Hemenway" <Jim@hemenway.com>
To: <largeformat@f32.net>
Sent: Monday, March 17, 2003 1:20 PM
Subject: Re: [LargeFormat] Process lenses... which one
should I get?


> Hi Folks:
>
> Thanks for the replies, I've decided on the 600mm.  It's
free and a
> Symmar and/or Sironar are not.  I broke the bank when I
bought the
> Symmar-S 360mm. It is clearly the best lens in my 11x14
kit.
>
> I spent some time the last several days making more 11x14
paper
> negatives with various lenses and developing them in the
kitchen sink at
> night with all lights out except the safe light. Did you
know that just
> a little bit of moonlight will fog the paper?  I ended up
taping
> newspapers over the kitchen windows above the sink for a
few days... I
> wonder what my fancy suburban Winchester neighbors thought
of that.
>
> The 210mm Apo-Gerogon and the 300mm APO Ronar will cover
8x10 well.  The
> 420mm APO Ronar covers 11x14 okay but the corners are
blurry... it is
> marginally acceptable for 11x14 at tiny apertures.
>
> I also tried the Protarlinse 300mm which came with my 8x10
Kodak Master
> camera, clearly not enough coverage for 11x14.
>
   Is this a single cell or a complete lens?  If its a
complete lens is should cover 11x14. A single cell will just
about cover 8x10.

> The other Protar, the shutter of which was fixed by SK
Grimes, turns out
> to have a lot of coverage for the 11x14.  This lens has
two aperture
> scales, (23 1/4 and 13 inches) and is the one which gave
me severe
> overexposure on the first try... I was probably using the
wrong aperture
> scale.  This afternoon, I'm now wondering if it isn't a
convertible.
> The front element is marked 23 1/4 inches and the rear has
no focal
> length marked on it at all. Together they appear to focus
on infinity at
> 300mm+ or about 13 inches. Would it make sense that the
front element
> can be used alone as a 23 1/4 lens?
>
> I've scanned all of the 11x14 paper negatives and plan to
put together a
> web page of/with them this week.
> --
>
> Jim - http://www.hemenway.com
>
  The Protar Series VII is a "convertible" lens. Each cell
can be used alone, or two cells can be used as a complete
lens. Coverage of the individual cells is no larger than the
complete lens although of longer focal length. Cells of
different focal length can be combined to get combinations
of various focal lengths providing the ratio of the two
focal lengths does not exceed about 1.4
  Speed of the individual cells is f/12.5, complete lenses
vary from f/6.8, for two cells of equal focal length to
f/7.7 for combinations at the greatest ratio.
  Individual cells of the Protar are corrected for coma. In
symmetrical lenses, like the Dagor, the individual cells are
not corrected for coma, the symmetry of the complete lens
being relyed on for that correction. Although the Dagor was
patented and sold as a convertible lens it really is not due
to the lack of coma correction in the cells.
  Series VII Protars were sold by both Zeiss and Bausch &
Lomb, who built them under Zeiss license, in sets of as many
as four cells along with a shutter and a barrel. The four
cells could be used singly or in combination for a great
variety of focal lengths. These were sometimes known as
casket lenses, from the packaging, or by the German term
Satz (sp?) for "set".
  When combined the longer focal length cell should always
be used on the front of the shutter or barrel. When used
singly the cells should, ideally, be on the rear of the
shutter because the stop position is important in minimising
several aberrations. However, the cells are slightly
retrofocus when used this way and slightly telephoto when
turned around, so, if you can tolerate a little field
curvature one can minimize the required bellows draw by
using the cells on the "wrong" side of the shutter or
barrel.
  Coverage of _combined_ Protars is about 70 to 75 degrees,
depending on the ratio of the combination. Coverage of the
single cells is only about 45 degrees, perhaps a little
more.
  The combined Protar has the same problem with zonal
spherical that the Dagor does. They tend to have a little
focus shift and to be a little soft when wide open, but
become very sharp when stopped down to perhaps f/16. Single
cells should be operated at f/32 or smaller to be sharp at
the margins.
  The combined Protar is an excellent lens. The single cells
are quite surprizingly good and have good color correction,
not always true of other convertible lenses.
  Wollensak built a version of the Protar under both the
Raptar and Velostigmat names. These are good lenses.
  I don't know what the quality difference between the Zeiss
and B&L versions of the Protar are exactly but, in general,
think Zeiss had better QC.
  There are several other lens designs based on Paul
Rudolph's original Protar. Most common are the Extra Wide
Angle Series V Protar, f/18, built by both Zeiss and B&L.
These were built as late as the late 1940's, at least by
B&L, and are included in both Zeiss and B&L's most elaborate
Convertible Protar sets. Coverage of this lens is about 100
degrees at around f/32. Despite the very slow speed the
ground glass image is bright enough to work with and image
quality is, again, quite surprizingly good.


---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com