[LargeFormat] Double Protar Lens

[Richard Knoppow]

----- Original Message ----- 
From: "Clive Warren" <cocam@blueyonder.co.uk>
To: <largeformat@f32.net>
Sent: Thursday, September 04, 2003 12:39 PM
Subject: Re: [LargeFormat] Double Protar Lens


> At 7:20 pm -0400 1/9/03, LNphoto wrote:
> Huge Snip
> >According to my 1911 catalog, a pair of 11 3/16" cells
give a
> >combinded focal lenght of 6 3/8" @ f6.3 and covers 4 1/2
x 7 1/4.
> >Something tells me in later years that was rounded to
5x7.    The 11
> >3/16" cell alone will cover 6x8 (whole plate) and has a
back focus
> >of 12 7/16".
> >
> >I have a couple of B&L double protars....enough to make a
D set.  I
> >also have C+ set from Zeiss.   While the glass may be
similar, you
> >have to remember these were made with "native"
machines.... The
> >Zeiss is metric through and through,  The B&L is Yankee.
The Ross
> >may be "stricken" with Whitworth threads, so that tube
may need
> >different threads at one end than the other.
> >
> >Les
>
> Les and Richard,
>
> I seem to have become the target of used Protar dealers
;-)
>
> There is now another set winging its way towards sunny
Bristol from
> the caves of Mordor in the North.  This time it is again a
set of
> same focal length cells, Bausch & Lomb - Zeiss Protar
Series VII
> Focus 16 1/8" both front and rear cells.
>
>  From what you have said, it seems that one of these would
have formed
> part of a D set? Presumably in a larger diameter barrel
than the C
> set. Perhaps your catalog has the info. for the combined
focal
> length..... would be great if the combined lens covers
8x10 however I
> have the feeling that you are going to tell me that the
combined FL
> is around 8".
>
> It seems almost certain that the previous lens is a pair
of 11 3/16"
> cells as you suggested. The stops are marked in the
Unified System
> which caused me some confusion initially f:16 = f/16 and
work from
> there......
>
> Cheers,
>         Clive
>

   From my undated but c.1910 B&L catalogue this is a No.13
Series VIIa Cells are both 16-1/8", combined focal length:
9-1/4", at f/6.3.  Covers 6x1/2 x 8-1/2 at full aperture.
This is an image circle of not quite 11 inches.
   The maximum image circle is around 80 degrees at f/45
(from experience, not the catalogue.) Individual cells have
about 40degree coverage, they are f/12.5.
  This catalogue shows only the "C" set.
  Any Series VII Protar can be used with any other provided
they are mechanically compatible and the ratio of focal
lengths does not exceed about 1.5X
  Stopped down the lens should cover 8x10 at around f/22 or
f/32. The image circle at f/45 should be around 14 inches,
maybe a bit more.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com