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An Equation
Old 07-05-2007, 04:49 AM   #1 (permalink)
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I was reading the text for my photo class a few days ago and came across this equation. E=IT Exposure=Intensity (times) Time

My question is this. If you were to re-write this formula, where would ISO fit into the equation? What about white balance?


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Re: An Equation
Old 07-05-2007, 05:13 AM   #2 (permalink)
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ISO affects the perceived intensity.

White balance has (pretty much) no influence on exposure.

Nice way to present your question - not sure that I'd have wanted my exam questions presented that way, however, because it's a tad distracting
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Re: An Equation
Old 07-05-2007, 05:51 AM   #3 (permalink)
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If I were to rewrite the equation, I would... well... I wouldn't rewrite it. E=I*T is not a calculation of exposure. It is an expression of equivalent exposure, i.e. reciprocity. As such, white balance is irrelevant. If I absolutely had to include ISO, it would be E=I*T*ISO. Increase any of the terms and one or two of the others needs to be decreased to keep the exposure constant. However, this changes the whole meaning of the equation, as changing the ISO implies changing the nature of your recording medium. E=I*T is meant to express the reciprocity characteristic of a given recording medium along the straight portion of the medium's characteristic curve. Outside the strait portion of the curve, the medium experiences reciprocity failure. I realize that I have made this about as clear as mud. I have been up for too many hours. Take a look at this:

http://en.wikipedia.org/wiki/Reciprocity_(photography)

and then hit the really technical description here:

http://micro.magnet.fsu.edu/primer/p...mexposure.html
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Re: An Equation
Old 07-05-2007, 10:26 AM   #4 (permalink)
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If I were your teacher, I would give you an A+ for your note taking.
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Re: An Equation
Old 07-05-2007, 12:54 PM   #5 (permalink)
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Quote:
Originally Posted by Murphy66 View Post
If I were your teacher, I would give you an A+ for your note taking.
I'll be sure to show him this thread, and see that he pays attention to your suggestion
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Re: An Equation
Old 07-05-2007, 12:58 PM   #6 (permalink)
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Quote:
Originally Posted by RobArtLyn View Post
Wow, just wow. That's a lot of info. Thanks.

Also, just as a side note, the wikipedia entry link you posted does not work, I think it's because the close parenthesis isn't attached to the link. But when you go to wiki and type in Reciprocity (photography) it works just fine. Thanks again for sharing. Lots to learn, better get going.
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Re: An Equation
Old 07-05-2007, 05:57 PM   #7 (permalink)
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Not sure how the link got messed up, but I have fixed it.
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