Weston Master Exposure Meters
A good general site for Weston exposure meters is the UK enthusiast site:
These are the exposure meters favored by Ansel Adams and used as the basis for his famous Zone system. I located a manual for the Weston Master II Exposure Meter on the Web, on the personal web site of Richard Urmonas:
This site has a wide variety of manuals, brochures, and catalogs from the pre-WW II era through the 1960's, particularly European camera, film, and equipment manufacturers. These are mostly in the form of B/W JPEG's for each page. I have converted his Weston Master II Exposure Meter manual and Weston Ratings booklet to PDF form to post here.
Weston Master II Manual
The Weston exposure manuals covered a wide range of models and types. Nearly all of them worked in similar ways. I have a Weston Master on hand and have observed an older metal-body Weston exposure meter, and, other than the shape and size of the case, the workings are exactly the same. They are selenium photocell (no battery needed or used) reflected light meters. The manual, in PDF form, is here (English, with French and Spanish summaries):
Weston Master Exposure Meter Manual (4.33 MB PDF file)
From the manual, the principal exposure meter output is in candles per square foot, or foot-candles. A foot-candle is 1/10.764 lux, where 10.7639 is the number of square feet in a square meter. There are two scales, 0-1600 and 0-50, a 32:1 fold-away baffle over the selenium cell selecting between them that selects between these two scales. This fact may be useful in working with this meter as an incident light meter, which is not treated in the manual.
A circular dial is used to set the film ISO speed and to match an arrow to the meter reading for scene average, a U mark for underexposure, and a O mark for overexposure, with one-stop markings around the arrow. Thus if you meter on a gray card, you can meter on other objects and the meter readings can be interpreted directly as Ansel Adams zones. The U mark is the center of zone 1 and the O mark is the center of zone 8 when the arrow is at the center of zone 5. Ansel Adams extended this to a science by calibrating zones at the scene to densities on the negative through standardized developing procedures, then to reflection densities on the print through standardized darkroom exposure and paper processing. Color processing standardizes processing, leaving only gamma, the ratio of contrast on the slide or print to light contrast, and exposure as the only variables, and the only variable available to the color photographer is exposure.
An interesting feature recommended for fast work in the manual is the direct reading feature. If you set the f/stop at f/11 for ISO 100 film, the reading in foot-candles is the shutter speed. You can scale this for other ISO speeds and other f/stops.
Weston Film Speed List (1958)
Weston tested most common films for IOS speed and published a table for use with its exposure meters. Richard Urmonas' web site included the 1958 edition, which, in PDF form, is presented here:
Weston Ratings (1.5 MB PDF)
The age of the file is shown by the fact that it gives speeds for Kodak Ektachrome E1 and E2 films, and the original ISO 10 Kodachrome. Kodacolor is listed as ISO 32 speed. Kodak B/W films are listed at between 1/3 stop and a full stop slower than the Kodak data sheets for the same films in the 1970's. Generally ISO speeds were 1/3 stop slower for tungsten or photoflood light than for daylight, but this may have been a function of the light coloration of the Weston meters, not the films.
An important disclaimer at the beginning of the Weston Ratings booklet is that its results apply to the Weston Master III Exposure Meter and that earlier Weston exposure meters should use 1/3 stop slower speeds.