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Beginner Question: Brightness range


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#1 Therese Kim

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Posted 16 January 2012 - 09:11 PM

Not sure it's appropriate for a beginner to post in this forum? But I've been scratching my head about a line in Blain Brown's "Lighting" book. It said that a subject with a brightness range of 1000:1 is 15 stops. I thought it would be 10? Would someone be willing to explain?
Thanks!
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#2 David Mullen ASC

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Posted 16 January 2012 - 09:40 PM

Not sure it's appropriate for a beginner to post in this forum? But I've been scratching my head about a line in Blain Brown's "Lighting" book. It said that a subject with a brightness range of 1000:1 is 15 stops. I thought it would be 10? Would someone be willing to explain?
Thanks!


I would think it would be 10 as well, but maybe I don't understand ratios enough. But if 2:1 is a 1-stop difference and 4:1 is a 2-stop difference, each doubling of light equals a stop, then a 10-stop difference should be 1024:1?

Found this online:
http://www.cambridge...namic-range.htm

Overall, the dynamic range of a digital camera can therefore be described as the ratio of maximum light intensity measurable (at pixel saturation), to minimum light intensity measurable (above read-out noise). The most commonly used unit for measuring dynamic range in digital cameras is the f-stop, which describes total light range by powers of 2. A contrast ratio of 1024:1 could therefore also be described as having a dynamic range of 10 f-stops (since 210 = 1024). Depending on the application, each unit f-stop may also be described as a "zone" or "eV."


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#3 M Joel W

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Posted 16 January 2012 - 10:35 PM

The difference between a very bright and very dark object (through a spot meter) is generally around 4-6 stops. In my experience, black fabric and white fabric are about four stops apart and I believe that the best black and white photographs approach six stops of contrast. Obviously reflective objects, street signs and reflective tape, specular highlights, and anything with UV dye pushes that a bit, but who meters for specular highlights?

My guess is the 15 stop figure refers to the approximate dynamic range of an average scene when lit with a 1000:1 (ten stop) contrast ratio. Especially since the book mentions the subject, not the ratio itself.

Edited by M Joel Wauhkonen, 16 January 2012 - 10:36 PM.

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#4 Chris Millar

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Posted 16 January 2012 - 11:16 PM

Not sure it's appropriate for a beginner to post in this forum? But I've been scratching my head about a line in Blain Brown's "Lighting" book. It said that a subject with a brightness range of 1000:1 is 15 stops. I thought it would be 10? Would someone be willing to explain?
Thanks!


Completely appropriate.

Without any further context you (and David) are right and he is wrong.

Joel, black and white material might only be 4~6 stops apart, but that is under constant illumination. Something 'black' outside a window in daylight might register as brighter than something white and lit in a metered interior.

When you talk about the best black and white photographs do you mean 6 stops of contrast captured and pushed through to the print as distinguishable tones, or 6 stops of reflective contrast on the print itself ?
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#5 M Joel W

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Posted 16 January 2012 - 11:35 PM

Joel, black and white material might only be 4~6 stops apart, but that is under constant illumination. Something 'black' outside a window in daylight might register as brighter than something white and lit in a metered interior.



No, Chris. Of course you're right but you misunderstand what I wrote. Under even illumination flat art is at most six stops (in reality closer to five stops) apart (in terms of diffuse, not reflective/specular light). So if you have a scene that's 1000:1 (ten stop contrast ratio), chances are the dynamic range of the scene is about 15 stops. So it's sloppy writing (and obviously the exact number varies based on subject), but since the book references the subject and not the lights themselves, a 1000:1 contrast ratio correlates generally with a roughly 15 stop subject dynamic range.


When you talk about the best black and white photographs do you mean 6 stops of contrast captured and pushed through to the print as distinguishable tones, or 6 stops of reflective contrast on the print itself ?


Six stops on the print itself.

Edited by M Joel Wauhkonen, 16 January 2012 - 11:40 PM.

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#6 Chris Millar

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Posted 17 January 2012 - 12:13 AM

I'm self taught via what makes sense (to me, which is a scary thought for some) so I guess it boils down to the definitions of dynamic range and contrast ratio.

What is your definition of contrast ratio ? (that distinguishes it from DR)
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#7 M Joel W

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Posted 17 January 2012 - 12:31 AM

At least in terms of how I approach it, contrast ratio is the key to fill ratio as read through the incident meter. So 1000:1 is a ten stop contrast ratio.

Dynamic range is the range from brightest value to darkest value in a given scene. So, assuming a 1000:1 contrast ratio, and assuming a subject with a roughly five stop range under even lighting (a big assumption, but one I'm guessing the author made), you'd end up with 15 stops of dynamic range in the scene through the spot meter.

It still doesn't totally make sense--each scene has a different color palette and five stops is a lot of contrast for flat art. But I think this is what the book is getting at. Either that or it's a typo! Anyway, what you and David have said makes perfect sense; I'm just not sure the author is outright wrong about this, though. I'm sure every capable DP or gaffer approaches this differently, just as some people light primarily with an incident meter (which makes a lot more sense to me, personally) and some with a spot meter.

I'm self-taught, too, excluding one intro course in school, so I could be wrong.

Edited by M Joel Wauhkonen, 17 January 2012 - 12:32 AM.

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#8 Chris Millar

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Posted 17 January 2012 - 12:43 AM

Key vs. fill on a grey card - or the darkest object in the fill compared to the brightest in the key ?
Include the sun in any shot and your DR will rocket ... I suppose a black hole would do wonders in the other direction Posted Image

I agree that in the end it's your output that counts - sometimes I've let myself believe things about aspects of my work as I've managed (despite myself) to produce good output in that field, but in describing it technically to someone I realise I'm talking out of my bum. Often just putting your hands over your ears is the best response...

Unless of course you hear voices ... telling you to do things ...

(radio earplugs)
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#9 M Joel W

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Posted 17 January 2012 - 01:38 AM

That's the idea, or at least my interpretation of it. As for light sources in scene, that's one time I personally use a spot meter--when a light, the sun or moon or clouds, an overcast sky, a lampshade, some 1000H, etc. is in frame. I guess in those cases the scene dynamic range is usually pretty extreme and the source just blows out, but I feel cool using a spot meter.

I'm sure photo printers would love to get their hands on some of that black hole emulsion, btw.

The best people I know work primarily intuitively, and I often feel embarrassed talking technically around them since their work far outstrips mine and with less pretense, but I'm a verbal thinker so I go through these cognitive hoops with any creative endeavor. You should read the (somewhat brilliant) twenty page neoformalist manifesto I wrote to pitch the horrible short film I never finished. Some day, hopefully, my work will speak for itself--or at least speak the same language I do.

Edited by M Joel Wauhkonen, 17 January 2012 - 01:40 AM.

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#10 Phil Rhodes

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Posted 17 January 2012 - 04:10 AM

But if 2:1 is a 1-stop difference and 4:1 is a 2-stop difference, each doubling of light equals a stop, then a 10-stop difference should be 1024:1?




That would be my interpretation of the language mentioned in this thread.


But I suppose it depends what you mean by "ratio" in that circumstance - people often confuse what a ratio really is, using real-world numbers either side of the colon as opposed to the lowest common denominators, etc.


And let's not even get into the relationship between stops and bits.


P
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#11 Chris Millar

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Posted 17 January 2012 - 04:17 AM

no, lets !

go on.

Edited by Chris Millar, 17 January 2012 - 04:18 AM.

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#12 Therese Kim

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Posted 17 January 2012 - 08:52 PM

I would think it would be 10 as well, but maybe I don't understand ratios enough. But if 2:1 is a 1-stop difference and 4:1 is a 2-stop difference, each doubling of light equals a stop, then a 10-stop difference should be 1024:1?

Found this online:
http://www.cambridge...namic-range.htm


Thank you! How cool--I read about you in "American Cinematographer!" Yes, it seems a 10-stop difference should be 1024:1. I didn't understand the "210=1024" in the quote, though.

Edited by Therese Kim, 17 January 2012 - 08:53 PM.

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#13 Therese Kim

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Posted 17 January 2012 - 09:13 PM

At least in terms of how I approach it, contrast ratio is the key to fill ratio as read through the incident meter. So 1000:1 is a ten stop contrast ratio.

Dynamic range is the range from brightest value to darkest value in a given scene. So, assuming a 1000:1 contrast ratio, and assuming a subject with a roughly five stop range under even lighting (a big assumption, but one I'm guessing the author made), you'd end up with 15 stops of dynamic range in the scene through the spot meter.

It still doesn't totally make sense--each scene has a different color palette and five stops is a lot of contrast for flat art. But I think this is what the book is getting at. Either that or it's a typo! Anyway, what you and David have said makes perfect sense; I'm just not sure the author is outright wrong about this, though. I'm sure every capable DP or gaffer approaches this differently, just as some people light primarily with an incident meter (which makes a lot more sense to me, personally) and some with a spot meter.

I'm self-taught, too, excluding one intro course in school, so I could be wrong.


Thanks to everyone who responded. The author's statement came from a subheading, "The Zone System." Here's are some excerpts from paragraphs preceding the statement in question:

"In evaluating exposure, we must look at a subject in terms of its light and dark values: the subject range of brightness...What we are measuring is subject brightness (luminance), which can vary in two ways: its inherent reflectance and the amount of light that falls on it. Reflectance is a property of the material itself..."

And here's the actual quote I'd paraphrased in my original post:
"The brightness range of a typical outdoor subject is about 1000:1. This is 15 stops, but here's the rub: imaging systems cannot reproduce this range of subject brightness..."
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#14 David Mullen ASC

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Posted 17 January 2012 - 11:03 PM

I didn't understand the "210=1024" in the quote, though.


I think the copied text just couldn't reproduce 210 correctly so it came out 210.
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#15 Therese Kim

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Posted 18 January 2012 - 08:15 PM

I think the copied text just couldn't reproduce 210 correctly so it came out 210.


Got it. Thanks!
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