Gray cards : the 12% - 18% controversy

Started Apr 13, 2013 | Questions
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cquarksnow Contributing Member • Posts: 518
Gray cards : the 12% - 18% controversy

http://dpanswers.com/content/tech_kfactor.php

Given spot-metering with a Merrill based camera, what percentage would seem appropriate for a gray card ?

Thanks,

Chris

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ANSWER:
Zone8 Forum Pro • Posts: 16,524
Re: Gray cards : the 12% - 18% controversy

The traditional Kodak Neutral Test Card (Grey  card) was 18% and specifically designed for using for colour transparency films as Zone 5 - and thus was never Zone 5 but actually Zone 6 for all negative films, something many writers of exposure system books did not seem to understand.  Thus if used as a midtone for exposure for negative films, the result was underexposure by one full f-stop.  With the original Kodak packets, containing two 10x8 cards, Grey one side and White the other, was a small printed leaflet actually indicating its intent.  Presumably, as with camera manuals and suchlike, was ignored or disbanded without being read.  

For transparency films - and thus digital sensors - the card was correct in sense of being Zone 5.  Of course, that does not mean creative exposure techniques as such but just a statement of fact.

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Hardy Steiner Senior Member • Posts: 2,442
Re: Gray cards : the 12% - 18% controversy

Yeah, there is a lot of talk about what's right and what isn't in regards to grey cards ... this seemed all too complicated to me, so I got myself an ExpoDisc ... just put it on front of the lens, point it against the light source with the lens in MF and then take the CWB shot ... easy as this.

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PicOne
PicOne Veteran Member • Posts: 6,923
Re: Gray cards : the 12% - 18% controversy

Hardy Steiner wrote:

Yeah, there is a lot of talk about what's right and what isn't in regards to grey cards ... this seemed all too complicated to me, so I got myself an ExpoDisc ... just put it on front of the lens, point it against the light source with the lens in MF and then take the CWB shot ... easy as this.

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I don't think the OP is talking about white balance at all.  He's talking about metering.

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Hardy Steiner Senior Member • Posts: 2,442
Re: Gray cards : the 12% - 18% controversy

yes, true I clearly wasn't paying enough attention.

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Hardy Steiner Senior Member • Posts: 2,442
Re: Gray cards : the 12% - 18% controversy

Actually, I just remember that you can use the Expodisc as an incident light meter as well ... just never used it therefore ...

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xpatUSA
xpatUSA Senior Member • Posts: 7,351
Re: Gray cards : the 12% - 18% controversy

cquarksnow wrote:

Given spot-metering with a Merrill based camera, what percentage would seem appropriate for a gray card ?

The well-respected Doug Kerr covers the subject at length here:

http://dougkerr.net/pumpkin/articles/Exposure_metering_18.pdf

and at even greater length here:

http://dougkerr.net/pumpkin/articles/Scene_Reflectance.pdf

The answer is not obvious, but it will be in there somewhere . . cuz he's the MAN!

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Roland Karlsson Forum Pro • Posts: 24,553
Re: Gray cards : the 12% - 18% controversy
2

cquarksnow wrote:

http://dpanswers.com/content/tech_kfactor.php

Given spot-metering with a Merrill based camera, what percentage would seem appropriate for a gray card ?

Personally I would say that the answer to this question has become less important in the digital era. If you take the time to use grey cards, you also have the time to take a test image, and look at the histogram.

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yvind Strm Veteran Member • Posts: 4,130
Re: Gray cards : the 12% - 18% controversy

edit

Zone8 wrote:

The traditional Kodak Neutral Test Card (Grey  card) was 18% and specifically designed for using for colour transparency films as Zone 5 - and thus was never Zone 5 but actually Zone 6 for all negative films, something many writers of exposure system books did not seem to understand.  Thus if used as a midtone for exposure for negative films, the result was underexposure by one full f-stop.  With the original Kodak packets, containing two 10x8 cards, Grey one side and White the other, was a small printed leaflet actually indicating its intent.  Presumably, as with camera manuals and suchlike, was ignored or disbanded without being read.  

For transparency films - and thus digital sensors - the card was correct in sense of being Zone 5.  Of course, that does not mean creative exposure techniques as such but just a statement of fact.

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Zone8: Although I am a handsome genius, when I stand in front of a mirror, I vaguely recognise the ugly idjit standing on the other side!
LINK: For B+W with Epson 1400 (and other models) using black ink only PLUS other useful tips:
http://www.photosnowdonia.co.uk/ZPS/epson1400-B&W.htm
Cleaning DSLR Sensors, including Kodak DSLR Factory Cleaning method:
http://www.photosnowdonia.co.uk/ZPS/KodakDCS-sensorcleaning.htm
Solving back/front focus problems on Sigma and most other DSLRs
http://forums.dpreview.com/forums/read.asp?forum=1027&message=35565277
PDF format list of lenses you can print or download - covers Italian Flag YES/NO for DCS 14n but applies to others. http://www.photosnowdonia.co.uk/ZPS/ItiFlagLensList.pdf

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Kind regards
Øyvind

yvind Strm Veteran Member • Posts: 4,130
Re: Gray cards : the 12% - 18% controversy

Careful, Roland.

I claim that using a grey card is much more precise than using the histogram.

Roland Karlsson wrote:

cquarksnow wrote:

http://dpanswers.com/content/tech_kfactor.php

Given spot-metering with a Merrill based camera, what percentage would seem appropriate for a gray card ?

Personally I would say that the answer to this question has become less important in the digital era. If you take the time to use grey cards, you also have the time to take a test image, and look at the histogram.

-- hide signature --

Kind regards
Øyvind

yvind Strm Veteran Member • Posts: 4,130
Re: Gray cards : the 12% - 18% controversy

edited

cquarksnow wrote:

http://dpanswers.com/content/tech_kfactor.php

Given spot-metering with a Merrill based camera, what percentage would seem appropriate for a gray card ?

Thanks,

Chris

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Kind regards
Øyvind

xpatUSA
xpatUSA Senior Member • Posts: 7,351
Re: Gray cards : the 12% - 18% controversy

cquarksnow wrote:

http://dpanswers.com/content/tech_kfactor.php

Given spot-metering with a Merrill based camera, what percentage would seem appropriate for a gray card ?

Thanks,

Chris

This is a transcript from one of the links by Doug Kerr that I posted earlier:

"Now, where can we get such a gray card of 12.8% reflectance? It isn’t easy. But we can easily acquire a gray card whose reflectance is 18%—all photo supply houses sell them. If we follow the scenario above with such a card as our “metering target”, the exposure recommended or set by the metering system will be 1/2 stop less than [that] needed to produce the effect we seek. (The greater illuminance seen from the 18% card will cause the metering system to feel that a lesser exposure is required than we [actually] need, by 1/2 stop). So, after we see the exposure that the metering system recommends (or actually sets) when the meter is regarding the 18% gray card, we [could] manually force the camera to use a 1/2 stop greater exposure and use that for the shot."

So, assuming the 'Merrill-based camera' to be compliant with the ISO standard, the answer to the actual question is . . .12.8%.

Having said all that, what's half a stop between friends?

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Ted http://kronometric.org
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cquarksnow OP Contributing Member • Posts: 518
Re: Gray cards : the 12% - 18% controversy

So, assuming the 'Merrill-based camera' to be compliant with the ISO standard, the answer to the actual question is . . .12.8%.

Having said all that, what's half a stop between friends?

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Regards,
Ted http://kronometric.org
SD9, SD10, EF-500, GH1.

Thanks to all ; this is very enlightening, and the only portion that is not confirmed is the ISO compliance of the Merrill-based cameras.

Chris

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jande9
jande9 Contributing Member • Posts: 845
Re: Gray cards : the 12% - 18% controversy

One problem with using a grey card is that it doesn't compensate for the direction of the light.

If you are in a side lit situation and hold up a card facing your lens and take a reading off that, any 3 dimensional object like a face will have the lit side overexposed.

If you try and compensate for that and hold the card facing the light and take your reading, shaded parts of the image will be underexposed.

People often take readings off the back of their hands, white skin being around 18% reflectance, and then turn their hands towards or away from the light to see how their exposure will change.

Incident meters are often supplied with a hemispherical bulb over the light cell to try and integrate the illumination over a three dimensional object.

I used a Sekonic Studio Incident light meter for many years, and you could turn the bulb towards the light or away from the light to see how your exposure would change depending on what part of the object was most important to you.  i still have it and use it occasionally, and I marvel at how photographically pleasing my results are using it.

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Roland Karlsson Forum Pro • Posts: 24,553
Re: Gray cards : the 12% - 18% controversy

yvind Strm wrote:

Careful, Roland.

I claim that using a grey card is much more precise than using the histogram.

The grey card method assumes even illumination of the scene. Something that is almost never the case. Even the direction of the card matters.

Moreover, if its very critical how to expose, I assume bracketing is a good idea. You are not wasting any film with digital

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Roland Karlsson Forum Pro • Posts: 24,553
Re: Gray cards : the 12% - 18% controversy

cquarksnow wrote:

Thanks to all ; this is very enlightening, and the only portion that is not confirmed is the ISO compliance of the Merrill-based cameras.

Considering how they treat color management, I assume that ISO compliance is not one of their main goals

To be more serious. Its my experience that different camera brands expose differently. So, they cannot all be ISO compliant. Moreover, the ISO compliance can only really be useful for spot metering. The averaged metering and the multi area intelligent metering do whatever they are programmed to do, which of course varies from camera to camera.

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xpatUSA
xpatUSA Senior Member • Posts: 7,351
Re: Gray cards : the 12% - 18% controversy

Not only that, ISO gives what they call "latitude" so, when you set ISO 100 on the camera, it could be anything between about 75-125. A good indication might be to shoot a gray card metered to zero plus half a stop and check the histogram (with as little processing as possible, esp. brightness and saturation) - it should show a narrow distribution in middle of the horizontal axis.

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Roland Karlsson Forum Pro • Posts: 24,553
Re: Gray cards : the 12% - 18% controversy

xpatUSA wrote:

Not only that, ISO gives what they call "latitude" so, when you set ISO 100 on the camera, it could be anything between about 75-125. A good indication might be to shoot a gray card metered to zero plus half a stop and check the histogram (with as little processing as possible, esp. brightness and saturation) - it should show a narrow distribution in middle of the horizontal axis.

The middle? How do you define that?

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xpatUSA
xpatUSA Senior Member • Posts: 7,351
Re: Gray cards : the 12% - 18% controversy
1

Roland Karlsson wrote:

xpatUSA wrote:

Not only that, ISO gives what they call "latitude" so, when you set ISO 100 on the camera, it could be anything between about 75-125. A good indication might be to shoot a gray card metered to zero plus half a stop and check the histogram (with as little processing as possible, esp. brightness and saturation) - it should show a narrow distribution in middle of the horizontal axis.

The middle? How do you define that?

A trick question, I suspect

I define the middle of the histogram's horizontal axis (assuming 0-255) as 127.

Of course, it could also be defined as 118 depending how gray you like your mid-gray . . .

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D Cox Forum Pro • Posts: 13,840
Re: Gray cards : the 12% - 18% controversy

yvind Strm wrote:

Careful, Roland.

I claim that using a grey card is much more precise than using the histogram.

I disagree with your claim.

But we could argue all night.

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