[LargeFormat] Some simple lens coverage tests with paper negatives

[Richard Knoppow]

----- Original Message -----
From: "Jim Hemenway" <Jim@hemenway.com>
To: "Large Format Group" <largeformat@f32.net>
Sent: Saturday, March 22, 2003 6:39 PM
Subject: [LargeFormat] Some simple lens coverage tests with
paper negatives


>>
> The 23 1/4 Protar used with both cells focuses at about
340mm.
>
> The Protarlinse which came with my 8x10 and which focuses
at about 310mm
> with both cells, vignettes. I didn't test it with the 41cm
or 59cm
> cells.
>
> http://www.hemenway.com/lens_coverage
>
> --
>
> Jim - http://www.hemenway.com
>
  I am curios about the 23-1/4 Protar, is this the marked
focal length of each cell? I can not find this focal length
listed as either a Zeiss or Bausch & Lomb lens.
  The closest FLs are:
 Zeiss; 23" two identical 23" cells having a combined FL of
13" at f/6.3 Coverage at small stops (probably f/45) 21-1/2"
  Bausch & Lomb; 23-1/8" Combined FL for two identical
cells; 13-1/4, f/6.3
  B&L states coverage at full aperture is sufficient for an
8x10 plate.
  Typically, a Convertible Protar with equal Fl cells has
coverage of perhaps 55 degrees wide open increasing to about
70 or 75 degrees at f/45.
  The individual cells cover about 45 to 50 degrees when
stopped down to about f/36 to f/45.
  My Zeiss Protar individual cells have surprizingly good
quality and the combined lens is excellent.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com