[LargeFormat] Carl Zeiss Protars

[Richard Knoppow]

At 09:39 AM 08/25/2002 -0700, you wrote:
>
>O>Richard,
>
>Thanks much,
>
>Not being set up for the telegraph, and probably would have a hard time 
>reaching 1920s Jena if I did, I'll pass on the codes, but I would like 
>to see the coverage of the  elements and combinations, and the speed of 
>the combinations.  When I was in the field I guessed.  One of the 
>benefits of using a Packard shutter is that you don't stress out on 
>whether or not it's f6.3, 7 or 7.7  There's something the BTZS people 
>can't say!
>
>
>"Packard shutters--ask the man who owns one".
>
   Single Protar cells are f/12.5 Typical coverage is about 53deg, i.e.,
the image circle is about equal in diameter to the focal length.  Zeiss
indicates the coverage reaches about 66deg at "small stops" meaning f/45.
   Single cells should be used behind the diaphragm. However, bellows draw
is significantly shorter when used in front of the diaphragm, the main loss
being some field curvature. 
  Speeds of combinations are:
Identical cells: f/6.3
Focal lengths in the approximate ratio of 1.25:1 are f/7.0
Focal lengths in the approximate ratio of 1.4:1  are f/7.7
 Cells of greater ratio should not be used together.
 The longer FL lens should be used on the front of the combination. 
  Note that the shortest and longest cells in a four lens set can not be
used together.
  Some shutters supplied with these sets are calibrated in millimeters
rather than f/stops. The lens sets came with calibration charts. For the
most part the pupilary magnification is close to 1 so the physical stop
size can be used as the f/stop size. Its easy to measure the effective size
if you want to be precise.
  Also note that the principal planes of single cells lie outside the cell.
When used behind the stop they are somewhat retrofocus, when used in front
of the stop they are slightly telephoto. 
  Series VII Protars are individually corrected for coma so perform fairly
well at larger stops, unlike a half Dagor which must be stopped down to
around f/45. 
  I have a Convertible Protar. The performance of the single cells is quite
surprizingly good and the performance of the combined lens is excellent.
Actually, I think the single cells are better than the single cells of the
covetible version of the Schneider Symmar although the combined lens is
probably not better.
  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