[rollei_list] Re: Hello (again), new Rollei TLR

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <rollei_list@xxxxxxxxxxxxx>
  • Date: Sat, 30 Apr 2005 01:06:31 -0700

----- Original Message ----- 
From: "Jerry Lehrer" <jerryleh@xxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Friday, April 29, 2005 7:47 PM
Subject: [rollei_list] Re: Hello (again), new Rollei TLR


> Richard,
>
> I am not surprised at your statement, I am ASTOUNDED!
> At one time I compared all my Weston meters, to a Luna
> Pro.  All the Westons had been checked out by QLM.
> They were in agreement after the corrected film speeds
> were used (Weston vs. ASA) The Westons ranged from
> the pre-Master 650 to the Euromaster II, except for that
> POS Master 6 (Japanese made toy)
>
> Jerry
>
   I discovered this when I was doing a quick comparison of 
meters and noticed that the exposures given by the Weston 
seemed low. I did direct comparison of three Weston meters, 
Two General Electric PR-1 meters, a Luna-Pro (my standard), 
a Sekonic Studio Standard (a modern version of the Norwood 
Director). All of the meters read the same. The Weston 
meters read the same if I set them for _half_ of the 
equivalent Weston speed, i.e., 40% of the ISO speed. This 
has to do with the way the calculator is set up not with the 
method of measuring the speed. I was also surprized because 
I can't understand why Weston did this. Evidently, they 
included a safety factor in the film speeds and then removed 
it in the calculator. The equivalent speeds from the old 
Kodak material prove this. Kodak speeds are double modern 
ISO speeds, and the Weston speed should be about 80% of 
this, but its not. It IS 80% of the original ASA speeds 
which included a large safety factor of 2.5X. Modern ISO 
speeds have a 1.25X safety factor. AFAIK, the Kodak speeds 
had no safety factor but the ASA speeds were 1/4 of them so 
perhaps they did.
   There are also exposure charts for these films which 
indicate the Kodak speeds were indeed about double current 
ISO speeds. Some may be surprized that film of EI-400 were 
available in the early and mid 1940's but they were. The 
difference between these and modern films is in much 
decreased grain and better resolution, and probably improved 
latitude.
   Probably the best reference on Weston meters and the 
Weston speed measuring method is the original article by 
W.N.Goodwin: "The Photronic Photographic Exposure Meter" 
W.N.Goodwin Jr., _Journal of the Society of Motion Picture 
Engineers_ V.20, p.95 (1933).
  I have also the patents for the Weston but I don't have a 
patent number on the speed method or know if it was 
patented.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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