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Re: [OM] Weston Meters

Subject: Re: [OM] Weston Meters
From: "John A. Lind" <jlind@xxxxxxxxxxx>
Date: Fri, 25 May 2001 01:09:13 +0000
At 00:35 5/25/01, Rich Lahrson wrote (in part):
It looks like the current one. I've got a reconditioned Master III. Back in the '50s, there wasn't a lot of choices in exposure meters and the Weston Master series was one of the most popular. Great meters! No batteries to replace or hassle with in the cold.

This is basic meter! Use one and learn the wonders of calculating exposure factors for lens extensions. With the earlier Western Masters, like the model II and III, the needle points to numbers that are candles-per-square foot.

Now, I don't fully konw how this works, but I picked it up years ago from the old Ansel Adams' Basic Photo series books: You get the square root of the ASA (like ASA 64, square root is 8) of the film you are using. That's your f-stop (in the example, f/8) and the meter dial indicates a number, the reciprical of which is the indicated shutter speed (like, 200 c/ft2 is 1/200 sec). Or, f/11 @1/00, etc. That's middle grey, the big arrow exposure. Those of you with this meter, if you haven't tried, check it out.

Well, enough math. The point is that this system is way faster, as the simple exposure calculations can be figured in the head So the exposure dial can be by-passed in many situations.

I don't know of any other meters which will read directly in c/ft2 like the old Weston meters. Of course these meters were popular before cameras generally had them built-in and automatic. Not all Weston models read directo c/ft2, just the earlier models.

See my tutorial about exposure and Exposure Value, or EV, the full name for which is the Additive Photographic Exposure System. Just after the introduction is a discussion of luminous intensity, flux, illumination, luminance, and what they all mean. Among other conversion is the one from Candles/ft^2 (now Candelas per square foot) to foot-Lamberts:
  http://johnlind.tripod.com/science/scienceexposure.html

BTW, Weston is one of the meters that uses *proper* units in this regard by using a true measure of luminance. Other meters I've seen are improperly marked with "foot-candles" or "lux" which are measures of _illumination_ not of _luminance_ which is what a photographic light meter really measures when making a reflected reading.

-- John


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