Help settle an argument!!

[ARMEE]

Hi
Help me settle an argument.
For studio work, what's best for white balance...A gray card or a
an Expodisc...Is one better than the other and if yes why??
Thank you.

[Wilt]

They both do the same thing, but the Expo disk has to be placed over the lens and pointed at the light source...wasted motion in a studio setting with the camera mounted on a tripod!


BTW, a gray card is either a device used for exposure, or it is a device for white balance setting. The fact that the gray card was made for WB does not make it suitable for exposure, and vice versa! Oddly, for some unkonwn reason, the gray-card-for-WB people don't make them in a tonality suitable for use as a reflective light meter target!

[ARMEE]

They both do the same thing, but the Expo disk has to be placed over the lens and pointed at the light source...wasted motion in a studio setting with the camera mounted on a tripod!


BTW, a gray card is either a device used for exposure, or it is a device for white balance setting. The fact that the gray card was made for WB does not make it suitable for exposure, and vice versa! Oddly, for some unkonwn reason, the gray-card-for-WB people don't make them in a tonality suitable for use as a reflective light meter target!

Thank you Wilt:
I got the first part..easy...
the second part is a bit confusing...can you please clarify..
or maybe it's me(dense i.e.).

Thank you very much..

[Wilt]

A gray card for exposure setting is, by convention, 18% gray tonality. The gray pigment used for the card may or may not be color neutral, however. If you photograph it in sunlight and use an eyedropper tool in post processing program, it might have values for R-G-B of 128-110-128 (in this example, deficient in Green), so it is useless as a White Balance tool because it would bias the result to have too much green (compensating for the lower G value of the card).

A gray card for WB might have R-G-B values of 160-160-160, which is color neutral, but useless for pointing a meter at that card to set exposure, because the departure from 128-128-128 makes it too bright in tonality, leading you to underexpose if you used that card for exposure determination.

[ARMEE]

A gray card for exposure setting is, by convention, 18% gray tonality. The gray pigment used for the card may or may not be color neutral, however. If you photograph it in sunlight and use an eyedropper tool in post processing program, it might have values for R-G-B of 128-110-128 (in this example, deficient in Green), so it is useless as a White Balance tool because it would bias the result to have too much green (compensating for the lower G value of the card).

A gray card for WB might have R-G-B values of 160-160-160, which is color neutral, but useless for pointing a meter at that card to set exposure, because the departure from 128-128-128 makes it too bright in tonality, leading you to underexpose if you used that card for exposure determination.

Got it:
Thank you very much Wilt for the detailed expalnation..:-)

[Player9]

Hi
Help me settle an argument.
For studio work, what's best for white balance...A gray card or a
an Expodisc...Is one better than the other and if yes why??
Thank you.


As your question involves white balance and not exposure, I would say that your best bet would probably be to use a totally neutral gray card (as explained in prior posts). You could put the card right up in the face of the model to take a reference shot that you would use in computer post processing to adjust all of the other shots from the same session. Even better, would be to use the card in every shot, by putting it in a strategically determined location that is close enough to the center of attention in the shot to be accurate, but far enough away to be cropped out in computer PP. This second method would totally eliminate any shot-to-shot inconsistencies in the color of the lighting.

[ARMEE]

As your question involves white balance and not exposure, I would say that your best bet would probably be to use a totally neutral gray card (as explained in prior posts). You could put the card right up in the face of the model to take a reference shot that you would use in computer post processing to adjust all of the other shots from the same session. Even better, would be to use the card in every shot, by putting it in a strategically determined location that is close enough to the center of attention in the shot to be accurate, but far enough away to be cropped out in computer PP. This second method would totally eliminate any shot-to-shot inconsistencies in the color of the lighting.
Thank you Player:
my reference: I took a studio lighting class and the "teacher" instructed us
to ask the model to hold up the gray card,take a full frame picture of it
and use this picture to set a custom white balance through the camera's
white balance menu.Then use the white side to set the exposure using
the histogram as reference.
First question:is this the method to use.
Second question:Will the expodisc do the same job as a gray card,or better
or worse.
Thank you for your help...confused soul....

[Curtis N]

A couple products worth considering:

WhiBal card:
http://www.rawworkflow.com/whibal/

Photovision calibration target:
http://www.photovisionvideo.com/store/shop.mvc?Screen=CTGY&Category_Code=DCT

I have both. The Photovision target produces slightly warmer images.

[moeronn]

I'm definitely no expert, but In a studio environment, assuming you aren't doing any drasting changes with gels, your white balance shouldn't change, right? You may use more or less light depending on placement and power of the strobes, but the color temp should be constant. Using the grey card once for in-camera custom white balance or taking a reading in PP once should be sufficient.

[FlyingPhotog]

For critical WB and Color Balance in a studio environment, get one of these:

Color Checker (http://www.amazon.com/GretagMacbeth-ColorChecker-Chart-Win-Mac/dp/B000E36T94/ref=pd_bbs_sr_2?ie=UTF8&s=miscellaneous&qid=1239143608&sr=8-2)

[umphotography]

For critical WB and Color Balance in a studio environment, get one of these:

Color Checker (http://www.amazon.com/GretagMacbeth-ColorChecker-Chart-Win-Mac/dp/B000E36T94/ref=pd_bbs_sr_2?ie=UTF8&s=miscellaneous&qid=1239143608&sr=8-2)


x2

eddie tapp uses this,,and in photoshop it makes things sooo easy. awesome tool,,,,may seem a bit pricey until you figure your time,,worth every penny.

[ARMEE]

A couple products worth considering:

WhiBal card:
http://www.rawworkflow.com/whibal/

Photovision calibration target:
http://www.photovisionvideo.com/store/shop.mvc?Screen=CTGY&Category_Code=DCT

I have both. The Photovision target produces slightly warmer images.
Sorry for delay in replying.
Thank you Curtis,I will certainly look them .

[ARMEE]

A big thanks for Moer..Flying..and Mike.

JC, I didn't know about this product but I will certainly look it up.
Cost in not an issue(within reason) ,i am trying to get the best results I can.
I don't own Photoshop but will buy it as it seems essential.

Again,I appreciate all your input.
Armand...

[Wilt]

i am trying to get the best results I can.
I don't own Photoshop but will buy it as it seems essential.

You do not need to buy pricey Photoshop to have WB adjustment! You can just as easily use Elements or Paint Shop Pro, at a fraction of the price of Photoshop. For example, PSP has an eye dropper tool that automatically balances WB to the color patch (perhaps the WhiBal card, for example) in the scene which you click on, no guessing what is 'right'. I presume Elements has that kind of tool, too.

[Curtis N]

While the RAW conversion features in Paint Shop Pro are lackluster at best, Canon's Digital Photo Professional is a very capable software package, and it's free!

[Wilt]

While the RAW conversion features in Paint Shop Pro are lackluster at best, Canon's Digital Photo Professional is a very capable software package, and it's free!

You assumed the OP shoots RAW...they could just as easily shoot JPG, which is what I assumed when suggesting PSP or Elements.

[Benji]

I'm definitely no expert, but In a studio environment, assuming you aren't doing any drasting changes with gels, your white balance shouldn't change, right? You may use more or less light depending on placement and power of the strobes, but the color temp should be constant. Using the grey card once for in-camera custom white balance or taking a reading in PP once should be sufficient.

I have been using an 18% gray card ever since I went digital nearly five years ago. I make an exposure of it at the beginning of EVERY session in the studio and I make an exposure of it EVERY time I shoot outdoors, and when I move to another location (regardless of whether it is 10 or 100 feet) I make an additional exposure of the card. It gives me perfect white balance every time.

I have discovered that moderate over or under exposure has no affect when checking the color temperature but differences in color temperature does affect exposure!

Benji

[vadim_c]

.... Even better, would be to use the card in every shot, by putting it in a strategically determined location that is close enough to the center of attention in the shot to be accurate, but far enough away to be cropped out in computer PP. This second method would totally eliminate any shot-to-shot inconsistencies in the color of the lighting.

Which dramatically increase the processing time as you need do something with that grey card in the image.
Shot-to shot inconsistency is not an issue enough that can be fixed with a greycard unless one uses a crappy cheapest strobes.

[eduardofrances]

For a good WB correction a gray card is an essential tool like the Whibal, but for critical color work nothing beats the Gretag Mcbeth color checker, even Broncolor users have this 2 tools in their bags.

[ARMEE]

You assumed the OP shoots RAW...they could just as easily shoot JPG, which is what I assumed when suggesting PSP or Elements.
Thank you Wilt:
Sorry for delay in response as I was away for three days.
You assume correctly,I always shoot in Raw and if need be Raw+small Jpeg.

[ARMEE]

I have been using an 18% gray card ever since I went digital nearly five years ago. I make an exposure of it at the beginning of EVERY session in the studio and I make an exposure of it EVERY time I shoot outdoors, and when I move to another location (regardless of whether it is 10 or 100 feet) I make an additional exposure of the card. It gives me perfect white balance every time.

I have discovered that moderate over or under exposure has no affect when checking the color temperature but differences in color temperature does affect exposure!

Benji

Thank you Benji..appreciate learning about your technique.

[ARMEE]

For a good WB correction a gray card is an essential tool like the Whibal, but for critical color work nothing beats the Gretag Mcbeth color checker, even Broncolor users have this 2 tools in their bags.

Thank you Eduardo:
I will certainly look into it.
At first glance which "version" of it do you use?as it looks there more than one.

[SkipD]

This color reference card (http://www.bhphotovideo.com/c/product/465286-REG/Xrite_MSCCC_Original_ColorChecker_Card.html) is the original ColorChecker card commonly known as the Gretag MacBeth ColorChecker card. X-Rite bought the maker of the card - see below.

The following was copied from Wikipedia's Color Chart (http://en.wikipedia.org/wiki/Color_Chart) page: A well-known and commonly used color chart is the Munsell ColorChecker—first produced as the Macbeth ColorChecker in 1976 and still widely known as the Gretag Macbeth ColorChecker—a cardboard-framed arrangement of twenty-four squares of painted samples based on Munsell colors. Its maker Munsell Labs and parent Gretag Macbeth were acquired in 2006 by X-Rite, a color management and colorimetry company.

[ARMEE]

This color reference card (http://www.bhphotovideo.com/c/product/465286-REG/Xrite_MSCCC_Original_ColorChecker_Card.html) is the original ColorChecker card commonly known as the Gretag MacBeth ColorChecker card. X-Rite bought the maker of the card - see below.

The following was copied from Wikipedia's Color Chart (http://en.wikipedia.org/wiki/Color_Chart) page: A well-known and commonly used color chart is the Munsell ColorChecker—first produced as the Macbeth ColorChecker in 1976 and still widely known as the Gretag Macbeth ColorChecker—a cardboard-framed arrangement of twenty-four squares of painted samples based on Munsell colors. Its maker Munsell Labs and parent Gretag Macbeth were acquired in 2006 by X-Rite, a color management and colorimetry company.

Thank you Skip,greatly appreciated.

[Tareq]

I m experimenting this color checker from Xrite, great tool, i always buy some important gear late.

[ARMEE]

I m experimenting this color checker from Xrite, great tool, i always buy some important gear late.

Tareq:
If you can share your experience with the board,I would greatly appreciate it.

[Tareq]

Tareq:
If you can share your experience with the board,I would greatly appreciate it.

It will take me long time as i have also gray cards, so i want to experiment all these cards with my light meter and see the results, as i can do many tests now but it may not be an accurate or scientific or logic tests, so i can't tell you now until i read and experiment more then i am more than pleased to post the results.

[Jim M]

You assumed the OP shoots RAW...they could just as easily shoot JPG, which is what I assumed when suggesting PSP or Elements.
I shoot RAW these days and use Elements, to the disgrace of my graphic artist son. I normally use Canon DPP for conversion, but I have used Adobe Camera Raw in Elements for conversion. DPP is just faster.

[Tareq]

I shoot RAW these days and use Elements, to the disgrace of my graphic artist son. I normally use Canon DPP for conversion, but I have used Adobe Camera Raw in Elements for conversion. DPP is just faster.

All my work is using DPP then Photoshop [CS2, or CS4], or FlexColor [for hasselblad RAW to convert first].

[James P]

I took a course from a world-travelled portrait photographer named Jean Francois O'Kane (http://www.thestudiocoach.com/). He had a model hold a gray card in front of her face, he then set his exposure from the card and used the image to set a custom white balance. The model discarded the gray card and the shot was taken. It turned out perfect. There are as many opinions as there are photographers, but in this case, the above method worked flawlessly and I've used it many times.

[Wilt]

I took a course from a world-travelled portrait photographer named Jean Francois O'Kane (http://www.thestudiocoach.com/). He had a model hold a gray card in front of her face, he then set his exposure from the card and used the image to set a custom white balance. The model discarded the gray card and the shot was taken. It turned out perfect. There are as many opinions as there are photographers, but in this case, the above method worked flawlessly and I've used it many times.


A many decades old, proven method for exposure setting with a reflected light meter, used in lieu of an incident light meter. For setting WB, the standard gray card may not be suitable with today's electronic tools (eye dropper used to set Auto color balance in post processing), as the color neutrality of 18% tonality gray cards may not be truly neutral in color balance.

However, when used as a means of assessing a print which is compared to the original card for tonality and color fidelity, it is also a many decades old, proven method for helping to set color balance when color fidelity was important during the film dominant era in photography.

[ARMEE]

I shoot RAW these days and use Elements, to the disgrace of my graphic artist son. I normally use Canon DPP for conversion, but I have used Adobe Camera Raw in Elements for conversion. DPP is just faster.
Jim:
can you explain to me why it's a disgrace to use Elements?
Thank you

[ARMEE]

I took a course from a world-travelled portrait photographer named Jean Francois O'Kane (http://www.thestudiocoach.com/). He had a model hold a gray card in front of her face, he then set his exposure from the card and used the image to set a custom white balance. The model discarded the gray card and the shot was taken. It turned out perfect. There are as many opinions as there are photographers, but in this case, the above method worked flawlessly and I've used it many times.
James:

you see this is when it's becomes confusing to me..
I took a one day free shoot in a studio and the "teacher" made the model
hold up the white side of the card foe exposure and the gray part for
the white balance.
As far as I can tell,the pictures came out fine.!!

[ARMEE]

A many decades old, proven method for exposure setting with a reflected light meter, used in lieu of an incident light meter. For setting WB, the standard gray card may not be suitable with today's electronic tools (eye dropper used to set Auto color balance in post processing), as the color neutrality of 18% tonality gray cards may not be truly neutral in color balance.

However, when used as a means of assessing a print which is compared to the original card for tonality and color fidelity, it is also a many decades old, proven method for helping to set color balance when color fidelity was important during the film dominant era in photography.
Thank you Wilt.
I think I understand..

[James P]

James:

you see this is when it's becomes confusing to me..
I took a one day free shoot in a studio and the "teacher" made the model
hold up the white side of the card foe exposure and the gray part for
the white balance.
As far as I can tell,the pictures came out fine.!!


I'm only a humble student of photography, but I've seen O'Kane's work and it's first rate, so I copy his methods whenever I can. I'm also aware that lots of other well qualified pros use different techniques to produce equally fine work. I guess we all find whatever works for us and go from there.

[ARMEE]

I'm only a humble student of photography, but I've seen O'Kane's work and it's first rate, so I copy his methods whenever I can. I'm also aware that lots of other well qualified pros use different techniques to produce equally fine work. I guess we all find whatever works for us and go from there.

James:
I agree 100% but you would think that there would be a "basic" method
to start with and experiment from there,no??

[Wilt]

James:

you see this is when it's becomes confusing to me..
I took a one day free shoot in a studio and the "teacher" made the model
hold up the white side of the card foe exposure and the gray part for
the white balance.
As far as I can tell,the pictures came out fine.!!


The reason for gray side is to avoid the issue of 'clipping' (too high of signal) causing the WB to be confused if one channel clips before the others...so that you do not get a wrongly biased result.

The use of white side for exposure is somewhat bizarre, but maybe he was simply adjusting that so the histogram moved those pixels to the right, thereby retaining detail in the highlights.

[SkipD]

You see this is when it's becomes confusing to me..
I took a one day free shoot in a studio and the "teacher" made the model
hold up the white side of the card foe exposure and the gray part for
the white balance.

The reason for gray side is to avoid the issue of 'clipping' (too high of signal) causing the WB to be confused if one channel clips before the others...so that you do not get a wrongly biased result.

The use of white side for exposure is somewhat bizarre, but maybe he was simply adjusting that so the histogram moved those pixels to the right, thereby retaining detail in the highlights.I agree 100% with Wilt.

The fellow was apparently NOT using a light meter to decide what exposure settings to use. It appears that he was merely using the white reference to create a peak on the histogram and adjusting exposure controls to get that peak to the right side of the histogram. This is, in my opinion, a rather silly and time-consuming way to determine exposure settings.

A far better way to determine exposure settings in a studio environment is to use either a handheld meter set up for incident readings (with a white hemisphere gathering the light) or a reflected light meter and a standard gray card. Either method measures the light falling on the subject rather than the light reflected from the subject.

If a flash source is used, the meter in a camera cannot measure the light. If the "teacher" did not have a handheld meter that could measure light from a flash source, that may be the reason that he used the oddball metering method. He was using a captured image and the histogram analysis of it to determine the exposure. Was the lighting from a flash source (or sources)?

[Faolan]

I use a WhiBal card for several reasons:

1) To make sure the exposure is correct
2) The colour balance before creatively tweaking
3) Black and white points to avoid clipping in post and print.
4) Consistancy for all shots from the session saving a lot of post work.

For colour critical work I've used the GretaMacbeth Colour reference card, but to get this to work properly you need a fully calibrated workflow.

They only take a few seconds to use so it's not a big issue but they can save hours, especially in complex white balanced environs.

The Expo disc can't do any of this other than make sure the exposure is ok and also that you've got a good balance.

[Tareq]

This is first Test i did in the studio by the Color Checker.

1.
http://img524.imageshack.us/img524/1595/test1a.jpg

2.
http://img524.imageshack.us/img524/2994/test1b.jpg

3.
http://img245.imageshack.us/img245/103/test2a.jpg

4.
http://img245.imageshack.us/img245/4200/test2b.jpg

I chose the "Florescent" as a WB in camera.
I used the profile created [in fact i didn't create a profile but i dragged the adjusted corrected layer] from #2 to correct #3.

[Tareq]

I will test with a WhiBal later and see what i will get.

[SkipD]

The WhiBal cards cannot be used for measuring exposure without using a significant offset value. Yes, they will provide a consistent target for a reflected-light meter, but they are quite a bit lighter than the required 18% gray (like a standard Kodak gray card is) and thus would have you underexposing your images by at least a full stop - maybe more.

I do have a full set of three WhiBal cards (wallet size to 8x10) that I use as a neutral color reference in different ways. They are very nice for that purpose.

The ExpoDisc cannot be used for anything but setting a custom white balance. That's it - nothing else. It cannot be used for setting exposure levels or even putting into a scene as a neutral reference. It is also VERY expensive for what little it can do for you and, in my opinion, a bit on the clumsy side to use.

[Faolan]

It can be used as such, if you have a good reading from the lightmeter for reference. It's the same principle as you would use levels in Photoshop to judge the image exposure. All you need to do is make a selection around the target and adjust.

It's a bit of a jury rig but it does work. Also I tend to shoot to the right in the histogram, so it doesn't really affect my workflow that much.

[Tareq]

I thought the OP was asking about "White Balance" and not "Exposure".

[Faolan]

It is, but it's a incidental conversation as to usage of the cards. He asked why one was better than another and the reasons... ;)

[Tareq]

It is, but it's a incidental conversation as to usage of the cards. He asked why one was better than another and the reasons... ;)

OK, for that part of question about the 2 cards fine, but he was looking for WB cards maybe, i may use that "Exposure" card for the "WB" but i may not get the accurate results because maybe i used the wrong tool, and then i will ask why that "Exposure" gray card didn't work fine for "WB" issue.

But i know that many answered him already, i am just new in this cards world and i am doing tests nowadays, i've got WB cards and Exposure card, including light meter which i have long time ago, so now i will work more on Exposure and WB.

[vadim_c]

Hi
Help me settle an argument.
For studio work, what's best for white balance...A gray card or a
an Expodisc...Is one better than the other and if yes why??
Thank you.
The key word is "Studio". If you have good lights you need neither.
The color is always the same, measure it once and use that value ever after.
It always works for me even though I tend to change the setup very often.
If you have AB or similar that drift color than things are getting a bit complicated but still it is possible to cope without measuring white balance every time.

[vadim_c]

The WhiBal cards cannot be used for measuring exposure without using a significant offset value. Yes, they will provide a consistent target for a reflected-light meter, but they are quite a bit lighter than the required 18% gray (like a standard Kodak gray card is) and thus would have you underexposing your images by at least a full stop - maybe more.
.
That is common misunderstanding. To measure exposure you need 12% grey card not 18%.
Google ANSI PH3.49-1971.

[Tareq]

That is common misunderstanding. To measure exposure you need 12% grey card not 18%.
Google ANSI PH3.49-1971.

Where can find that 12% gray card?

[Wilt]

That is common misunderstanding. To measure exposure you need 12% grey card not 18%.
Google ANSI PH3.49-1971.

Nope! 12% grey happens to be the standard for CALIBRATION of a meter, testing to the ANSI standard...corresponding to the incident meter light level used for calibration.

Exposure is measured to the 18% gray mean scene brightness that Kodak engineers discovered a very long time ago.

[ARMEE]

I agree 100% with Wilt.

The fellow was apparently NOT using a light meter to decide what exposure settings to use. It appears that he was merely using the white reference to create a peak on the histogram and adjusting exposure controls to get that peak to the right side of the histogram. This is, in my opinion, a rather silly and time-consuming way to determine exposure settings.

A far better way to determine exposure settings in a studio environment is to use either a handheld meter set up for incident readings (with a white hemisphere gathering the light) or a reflected light meter and a standard gray card. Either method measures the light falling on the subject rather than the light reflected from the subject.

If a flash source is used, the meter in a camera cannot measure the light. If the "teacher" did not have a handheld meter that could measure light from a flash source, that may be the reason that he used the oddball metering method. He was using a captured image and the histogram analysis of it to determine the exposure. Was the lighting from a flash source (or sources)?

Skip:
thank you for your answer.
I will elaborate. there was 2 fellows running the "show",one was a light meter type and the other I guess had a light meter built in his eyes.
The first guy did say to use a light meter reading off each light to determine
the ratios and suggested moving the strobes back n forth as not to get
readings between f stops(like 8.3 etc) but rather f8.0 etc.
And then take a reading off the model facing the camera to set it.
It all made sense then.
From what I understand (correct me if I am wrong) the white side
of the card will serve for setting the custom white balance through
the menu of the camera.
I do apologize for rambling on.

[ARMEE]

I use a WhiBal card for several reasons:

1) To make sure the exposure is correct
2) The colour balance before creatively tweaking
3) Black and white points to avoid clipping in post and print.
4) Consistancy for all shots from the session saving a lot of post work.

For colour critical work I've used the GretaMacbeth Colour reference card, but to get this to work properly you need a fully calibrated workflow.

They only take a few seconds to use so it's not a big issue but they can save hours, especially in complex white balanced environs.

The Expo disc can't do any of this other than make sure the exposure is ok and also that you've got a good balance.
Faolan:
Thank you for you explanation, is white clipping when it flashes in
the histogram?

[ARMEE]

I will test with a WhiBal later and see what i will get.
Thank you Tareq

[ARMEE]

Nope! 12% grey happens to be the standard for CALIBRATION of a meter, testing to the ANSI standard...corresponding to the incident meter light level used for calibration.

Exposure is measured to the 18% gray mean scene brightness that Kodak engineers discovered a very long time ago.
Wilt:
Can you please clarify the 12...18% ,
Me,too , I thought it was 18% gray....:o

[Wilt]

Wilt:
Can you please clarify the 12...18% ,
Me,too , I thought it was 18% gray....:o

The ANSI standard deals with meter calibration. It specifies that reflected light meters are calibrated to, “an area of known uniform luminance which covers completely the whole field of view of the meter”, and that incident light meters are calibrated, “to a point source of light of known luminous intensity located on the meter axis”.

There are equations provided within the standard, one for calibration of reflected light meter and one for incident light meters. If one attempts to derive a reflected light level equivalent to the incident light intensity, one ends up with about 13% tonality surface. So per the standard, reflected light meters should be calibrated to about 12-13% gray, with an allowable error of plus or minus 1-2%.

But calibration to a standard is not the same as deriving an exposure value for a given level of light and average scene brightness. A snow scene or a sandy beach is not 'average' in scene brightness, nor is a coal mine with a black cat inside. But the 18% tonality is not only representative of the 'average' scene, but it also happens to be the midpoint in a 9 level range of photographic brightnesses ( the Zone system!) And if you take an R-G-B mix of 128-128-128 (where 256 is the max value of each color), you get 18% gray as the output.

Holding an 18% card at an angle is not the same as making it appear to be 12% in brightness, it is merely avoiding the issue of surface sheen reflecting MORE light to a meter than the inherent 18% tonality of the card. On that point, the David Spiegelman article is incorrect! Put that 18% card into diffuse light, with no surface sheen, and it registers 18% gray and gives you the right exposure.

[ARMEE]

The ANSI standard deals with meter calibration. It specifies that reflected light meters are calibrated to, “an area of known uniform luminance which covers completely the whole field of view of the meter”, and that incident light meters are calibrated, “to a point source of light of known luminous intensity located on the meter axis”.

There are equations provided within the standard, one for calibration of reflected light meter and one for incident light meters. If one attempts to derive a reflected light level equivalent to the incident light intensity, one ends up with about 13% tonality surface. So per the standard, reflected light meters should be calibrated to about 12-13% gray, with an allowable error of plus or minus 1-2%.

But calibration to a standard is not the same as deriving an exposure value for a given level of light and average scene brightness. A snow scene or a sandy beach is not 'average' in scene brightness, nor is a coal mine with a black cat inside. But the 18% tonality is not only representative of the 'average' scene, but it also happens to be the midpoint in a 9 level range of photographic brightnesses ( the Zone system!) And if you take an R-G-B mix of 128-128-128 (where 256 is the max value of each color), you get 18% gray as the output.

Holding an 18% card at an angle is not the same as making it appear to be 12% in brightness, it is merely avoiding the issue of surface sheen reflecting MORE light to a meter than the inherent 18% tonality of the card. On that point, the David Spiegelman article is incorrect! Put that 18% card into diffuse light, with no surface sheen, and it registers 18% gray and gives you the right exposure.


Thank you Wilt..