EV (Exposure Value) to LUX

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EV (Exposure Value) to LUX

Postby bngoofy » Thu Jan 22, 2004 10:30 pm

Any idea how to do this?
bngoofy
 

Re: EV (Exposure Value) to LUX

Postby Knight » Fri Jan 30, 2004 3:06 am

bngoofy wrote:EV (Exposure Value) to LUX
Any idea how to do this?

The definition of EV=0 is an exposure of 1 second at f/1 using ISO 100 film, or any equivalent thereof (2 seconds f/1.4, 4 seconds f/2.0 etc)

The technical definition of Ev is 2Ev = LS/C.

Where:

• Ev = the exposure value
• L = field luminance
• C = Exposure Constant - If you use candelas/ft2, it is 1.3. If you are using LUX (candelas/m2), it is 12.5.
• S = film speed following the ISO standard

Now, as far as where I think you're trying to go with this... Consider that 2ev = A2/T

where:

• A = the f-stop number of the aperture
• T = shutter time in seconds

Combining these two; EV = log2(A2/T) = log2(LS/C) - This is perhaps the most vital formula there is for understandiing the basics of the mathematics behind photography.

I hope this helps!
William J. Knight
Health Physicist
Los Alamos National Labs
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