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post #121 of 122 Unread 08-05-2016, 01:11 PM
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Originally Posted by DLCPhoto View Post
So then, is my prior statement correct in how to incorporate those numbers when trying to get an effective 14-16 footlamberts coming off the screen?
Here is how I incorporate the screen gain, for a close estimation of how many foot lamberts I'm watching at. My screen - a 122" diagonal 16:9 screen - is 43.87 square feet in size. Here's what I measured my Sony VW600 at, at one point last year - 222 Lux divided by 10.76 = 20.631 X 43.87 = 905.12 lumens, x 1.1 ( screen gain ) = 995.63 divided by 43.87 = 22.69 foot lamberts. Now, Accucal says that my Neve screen is really closer to 1.25 gain, so that actually puts me at 25.78 foot lamberts.

You really are just trying to get a good idea where you are foot lambert and brightness wise. And hopefully one can re - check over time to see how their lamp is holding up. It isn't perfect, but it's much better than not using a light meter at all - then you have absolutely no idea how bright ( or dim ) your picture is, and whether it's your lamp or your eyes that are failing !!
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post #122 of 122 Unread 08-06-2016, 06:08 PM
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Originally Posted by Craig Peer View Post
Here is how I incorporate the screen gain, for a close estimation of how many foot lamberts I'm watching at. My screen - a 122" diagonal 16:9 screen - is 43.87 square feet in size. Here's what I measured my Sony VW600 at, at one point last year - 222 Lux divided by 10.76 = 20.631 X 43.87 = 905.12 lumens, x 1.1 ( screen gain ) = 995.63 divided by 43.87 = 22.69 foot lamberts. Now, Accucal says that my Neve screen is really closer to 1.25 gain, so that actually puts me at 25.78 foot lamberts.
You're kind of overcomplicating things here There's no point converting back and forth to lumens. Just measure the Lux, or better yet, if your meter will display foot-candles, measure that, and then multiply that by your gain value. And that's your fL.

So for your numbers all you have to do is take 222 Lux, divide by 10.76 to get 20.6 foot-candles. Multiply by 1.25 to get ~26fL. Of course none of this is accurate enough for rigorous scientific testing, but for just setting your aperture in the ballpark of 16fL or measuring brightness change over time, it's good enough.

Or it's really easy if you've got a meter that can be set to display foot-candles, then you just measure, you'd get 20.6 fc right off the meter, multiply by 1.25 to get ~26fL, and you're done.

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