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What does EV mean?

Bert Krages , Sep 09, 1999; 10:35 a.m.

One of the specifications for exposure meters is EV. Although I have checked several books, I have been unable to find out what the term means or how to use it. Can anyone tell me how to figure out what shutter speeds and apertures correspond to a particular EV value? Thanks.


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Jacques Desjardins , Sep 09, 1999; 10:54 a.m.

EV stands for "Exposure Value" and a 1 second exposure at F1 is EV 0, 1 second at F1,4 is EV 1 and so on.

John Robison , Sep 09, 1999; 10:59 a.m.

EV means exposure value, and is a measure of light intensity. Determination of shutter speed and aperture for a particular light level requires that you know the film rating and make a judgement as to the color and quality of the light. Most modern light meters give a direct readout of base shutter and aperture settings given a film speed input.

Jacques Desjardins , Sep 09, 1999; 11:03 a.m.

I'm sorry, I forgot to ad that the parameters I gave were for ISO 100 film.

Ellis Vener , Sep 09, 1999; 11:36 a.m.

It means me: Ellis Vener. Light brightness is now measured in units of Ellis Veners. I was able to change the official notation system while everyone was worried about 9/9/99 Cobal crashes and the Y2K thingy.

By the way this question has asked before here on photo.net and if you had looked through the categories involving lighting or miscellaneous you have found the real answer and avoided my silly one.

Alan Gibson , Sep 09, 1999; 11:46 a.m.

Jacques's second post is incorrect. His first post is correct for all film speeds.

Fritz Brown , Sep 09, 1999; 11:55 a.m.

In embryologic research there is a measure of the distance across the suface of an embryo that is in the units of "sturts" which were named after the guy, Sturtevant, who worked in the area. So why cant we measure light in "Ellis Veners". Then we could come up with another measure in units of "Dan Smiths" that could be aplied to the quality of an image. With a 10 on the DS scale being a masterpiece to be hung in the Louvre and 0 DS being an image that you really don't want to hear whan Dan has to say about it. (Me thinks that there would be a lot of ones and twos assigned to images posted for critique here in the past). 8)

Christopher Hawkins , Sep 09, 1999; 12:07 p.m.

From: http://photo.net/photo/optics/lensTutorial.html

Ev = Av + Tv = Sv + Bv

where: Ev = Exposure Value Av = Aperture Value = lg2 N^2 where N = f-number Tv = Time Value = lg2 (1/t) where t = time in sec.s Sv = Speed Value = lg2 (0.3 S) where S = ASA speed Bv = Brightness Value = lg2 Bfl lg2 is logarithm base 2 from which, for example: Av(N=f/1) = 0 Tv(t=1 sec) = 0 Sv(S=ASA 3.125) E Bv( Bfl = 1 foot-Lambert) = 0 and therefore: Bfl = 2^Bv Ev (Sv = 0) = Bv

Matthew Francey , Sep 09, 1999; 12:23 p.m.

Hasn't this been asked before? [Search...search] Yep. Click on "film", under the "Q&A" page, and search that page for "EV".

[DS units]

Closed, linear, scales are usually bad design. Ask rock climbers and white water kayakers: they know. The geologists, too, botched it with the initial Richter scale. But at least they had the presence of mind to go to an open-ended system. So should photography. Hence the "DS" scale should be open at both ends, and like the EV unit, be logarithmic. We need only find two standards, assign them measures on the DS scale and the rest is simple. I might suggest we assign a typical family snap-shot a "0", and maybe Adams' "Moonrise" a 10. Under this system, more than a few of the images offered for critiques here would come in as negative numbers... Actually, most of the photographs I take would be multi-digit negative numbers. ;-(

Tony Rowlett , Sep 09, 1999; 12:28 p.m.


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