[LargeFormat] Carl Zeiss Protars

[Richard Knoppow]

At 03:00 PM 08/25/2002 -0700, you wrote:
>
>On Sunday, August 25, 2002, at 02:04 PM, Richard Knoppow wrote:
>
>> At 09:39 AM 08/25/2002 -0700, you wrote:
><bigsnip>
>>
>
>>
>>   I have a Convertible Protar.   Protar sets, either B&L or Zeiss, seem 
>> to be quite rare on the used
>> market.
>> ----
>> Richard Knoppow
>> Los Angeles, CA, USA
>> dickburk@ix.netcom.com
>>
>
>As I have said before I have the Zeiss C set, but I've also aquired the 
>4 cells of a B&L D set.  I've got some questions regarding distance the 
>cells should be from the shutter.  Which set do you have?
>
>Les
>
  I don't have the full set. I have a 35cm and 29cm cell in a dial set
Compur shutter. This combination was sold as a stock item. Its f/7.7,
equivalent FL 185mm. 
  There are two patents covering the Series VII protar. The first is USP
532,398 (Jan 8, 1895) the second, USP 1,021,337 (Mar, 16, 1912). The
spacing in the two are slightly different. In the older version the
distance from the apex of the rear element to the stop is 0.017 of the
focal length. In the second patent its given as 0.0234 of the focal length.
Note that this is the FL of the _cell_ not the entire lens.	
 On my lens the distance from the diaphragm to the center of the rear
element comes out to about 0.2*FL for both sides and is different for the
two cells. 
  I forgot in my original post that the coverage of the combined lens
varies from about 80 degrees for two identical cells to about 75 degrees
for the maximum ratio (f/7.7) at f/45. Plate size wide open indicates
coverage of about 60 degrees for all combinations. Zeiss tends to be
conservative in its coverage figures. 
  Like Dagors, and other double meniscus type lenses, the Protar tends to
have some uncorrected zonal spherical aberration, leading to some focus
shift. Most of this is gone after stopping down about two stops from
maximum.   
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com