[LargeFormat] plastigmat lens

[Richard Knoppow]

At 06:07 PM 08/21/2002 -0400, you wrote:
>Mr. Warren, I have a copy from the B&L catalog that list the plastigmat
>lenses available. It's my understanding that these were made as early as
>1900. If I recall, the front and rear elements were each made of 4 glass
>elements cemented together. They were like anastigmats in that either
>the front or rear elements could be used separately. The plastigmat I am
>interested in was code named by B&L by the name "Plastpox". This
>particular lens was 4 inches in diameter (unmounted) and had a focal
>length (both lens elements) of 26 inches (52 inch fl for individual
>elements).  I'm interested because of research on an 11 ft. x 6 ft. x 5
>ft. camera that was used to make 1.33 times life size negatives, from
>which large contact prints (5 ft. x 30 in.) were then made. If you have
>any information about the existence of this lens, I'd be glad to hear of
>it.
>
>Thanks,
>
>Charles (Huntsville, AL)
>
>
  FWIW, the patent for the Plastigmat is USP 660,747 (1900) issued to
Edward Bausch. 
  The lens is listed in the 1907 B&L lens catalogue. One longer FL is
listed, a 29-1/2 inch lens. 
  The only coverage data given is that the 26" lens will cover a 16x18 inch
plate at f/6.8. Assuming it behaves like a Protar, which it resembles in
general type, it should have significantly larger coverage at small stops,
up to perhaps 80degrees. Since a lens covers an image circle at 1:1 twice
the diameter of its infinity coverage this lens would just about make it
for the size format mentioned. 
  The single cells of convertibles have no larger image circles than the
combined lens despite the nearly double focal length. 
  The catalogue does not list the FL of the individual cells but they
should be around 1.8X the combined FL. Remember, the spacing between the
cells must be taken into account in calculating the combined FL.
  A slightly later (but undated) B&L catalogue no longer has the Platigmat,
perhaps because it was competing head to head with the Protar.
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com