Gray Card for Exposure Help

[Strodav]

When I first started using Tri-X 400 film developed with HC110, I studied and started using the zone system as part of my photography journey. When I moved to digital and began understanding the capabilities of my cameras and PP software, the zone system became moot as I now set exposure using the histograms displayed in the camera (or pay attention to the blinkies) and can adjust the tone reproduction curve(s) in post. I usually take a picture of a gray scale on shoots mainly to set white point in Post, but the days of assigning a part of a scene to a specific zone are over for me. As long as the DR of the scene is less than or equal to my camera's DR I am good to go. If the DR of the scene exceeds my camera's ability, then I choose to either bury the shadows or blow out the highlights, but I still have the ability to adjust the tone curves in Post.

 

[JBPhotog]

Exposure calibration is not the same as White Balance and there seems to be some confusion in this thread mixing the two.

FWIW, a known standard is important if you trying to achieve the precise exposure based on a calibration point. Incident and reflected meters are calibrated at 18%, thus the reason Kodak and Sekonic grey cards are also 18%.

Whether the photographer chooses to set the exposure from an 18% grey card is totally subjective.

 

[Strodav]

Exposure calibration is not the same as White Balance and there seems to be some confusion in this thread mixing the two.

FWIW, a known standard is important if you trying to achieve the precise exposure based on a calibration point. Incident and reflected meters are calibrated at 18%, thus the reason Kodak and Sekonic grey cards are also 18%.

Whether the photographer chooses to set the exposure from an 18% grey card is totally subjective.

I'm trying to understand your point. A gray card is a great reference to help adjust white point in Post, but is no longer needed to set exposure with modern digital cameras so what is "precise exposure"? If the DR of my camera was greater than the DR of my scene when I took the shot, then I can adjust exposure to my heart's content in Post and using tone curve(s) to map any input value to any output value I want (within reason) and I can easily expand or shrink the DR of the scene. So I don't understand why "precise" exposure is needed if the DR of my camera can capture the DR of my scene. If I had to bury the shadows or blow out the highlights because of an HDR situation, which the histogram or blinkies showed when taking the shot, I can still adjust the exposure to my heart's content as long as I know I can't recover the buried shadows or blown out highlights, which is why many of us bracket in HDR situations then fix it in Post.

 

[JBPhotog]

I'm trying to understand your point. A gray card is a great reference to help adjust white point in Post, but is no longer needed to set exposure with modern digital cameras so what is "precise exposure"? If the DR of my camera was greater than the DR of my scene when I took the shot, then I can adjust exposure to my heart's content in Post and using tone curve(s) to map any input value to any output value I want (within reason) and I can easily expand or shrink the DR of the scene. So I don't understand why "precise" exposure is needed if the DR of my camera can capture the DR of my scene. If I had to bury the shadows or blow out the highlights because of an HDR situation, which the histogram or blinkies showed when taking the shot, I can still adjust the exposure to my heart's content as long as I know I can't recover the buried shadows or blown out highlights, which is why many of us bracket in HDR situations then fix it in Post.

Your premise that precise exposure is of no value with a digital camera is simply not true. The DR of a scene can easily outstrip the DR of your sensor and knowing the actual range that can be captured based on your ISO is a useful tool. Sekonic make a high quality grey target and software to calibrate the DR of your camera and BTW, the grey card is 18% grey. Back in the film days a Kodak grey card, B&W film stock, your camera, a sunny day and densitometer were the tools used to determine meter calibration. These days software and a high quality known grey target can do the job.

I don't disagree, a white sheet, a piece of white foam board etc. etc. can be useful in WB but they don't help with exposure unless you do extensive testing to know exactly their reflective percentage.

 

[Strodav]

I'm trying to understand your point. A gray card is a great reference to help adjust white point in Post, but is no longer needed to set exposure with modern digital cameras so what is "precise exposure"? If the DR of my camera was greater than the DR of my scene when I took the shot, then I can adjust exposure to my heart's content in Post and using tone curve(s) to map any input value to any output value I want (within reason) and I can easily expand or shrink the DR of the scene. So I don't understand why "precise" exposure is needed if the DR of my camera can capture the DR of my scene. If I had to bury the shadows or blow out the highlights because of an HDR situation, which the histogram or blinkies showed when taking the shot, I can still adjust the exposure to my heart's content as long as I know I can't recover the buried shadows or blown out highlights, which is why many of us bracket in HDR situations then fix it in Post.

Your premise that precise exposure is of no value with a digital camera is simply not true. The DR of a scene can easily outstrip the DR of your sensor and knowing the actual range that can be captured based on your ISO is a useful tool. Sekonic make a high quality grey target and software to calibrate the DR of your camera and BTW, the grey card is 18% grey. Back in the film days a Kodak grey card, B&W film stock, your camera, a sunny day and densitometer were the tools used to determine meter calibration. These days software and a high quality known grey target can do the job.

I don't disagree, a white sheet, a piece of white foam board etc. etc. can be useful in WB but they don't help with exposure unless you do extensive testing to know exactly their reflective percentage.

Started in film and still have my Lunapro light meter and original Kodak 8x10 grey cards and McBeth color checker made in the 1980s. Yes, I used them with my film cameras, but no longer need them as I have a built in spot meter and histograms with blinkies in my digital cameras. I use to test the DR of a bulk roll of Tri-X 400 in my AE-1 to get exposure in line with the Zone system, but never felt the need to do the equivalent with digital cameras. Am I missing something. Please define “precise exposure” for me. As an Engineer I am always trying to learn new things.

 

[smoke665]

Your premise that precise exposure is of no value with a digital camera is simply not true. The DR of a scene can easily outstrip the DR of your sensor and knowing the actual range that can be captured based on your ISO is a useful tool.

Isn't the concept of a "precise exposure", also ambiguous? As you say the DR of the scene vs the capability of the sensor limit your exposure, but so does the capability of the medium of display.

I've seen varying arguments on the capabilities of the human eye ranging from 15-24 stops. More than enough to outdo most sensors. Then you have the limitation of the RGB model in an 8 bit display with its 256 levels of gray. According to the NIH in a paper on medical equipment going to a 10 bit monitor with its 1024 levels of gray, they found human observers could actually discern up to 870 levels of gray. Increasing the Number of Gray Shades in Medical Display Systems—How Much is Enough?. In film/print you get into the same limitations the moment you convert the negative to a digital file. Bypassing the digital step, going straight to print still has the limitation of the paper. Your whites can only be as white as the paper, and your blacks as black as the emulsion/ink is capable of producing.

Like the question "is there sound from a tree falling in the forest with no one to hear", just because we cant see it, or our equipment doesnt display it, doesnt mean it doesnt exist. At best any image captured is but a slice of what's available. IMO rather than getting hung up on the unobtainable, it's more realistic to consider how the exposure fits the composition. I know of many photographers who routinely blow the whites in a High Key image or under expose the shadows to protect the highlights, because it better fits their interpretation of the scene. I personally prefer to strive for a full data file based on the histogram.

 

[JBPhotog]

IIRC, Kodak also stamped the date of production on the packaging of their grey cards so if you are using one from the 1980's don't expect it to still be 18% grey or for that matter neutral in its RGB values, over time the coating fades thus making it unreliable. My Sekonic Exposure Profile Target II comes in a black opaque sleeve to protect it from unnecessary fading and instructs the owner not to touch the surface and keep it stored properly.

Isn't the concept of a "precise exposure", also ambiguous? As you say the DR of the scene vs the capability of the sensor limit your exposure, but so does the capability of the medium of display.

In a word, no. The quantity of the light on the subject has a specific value, it is this exposure value that is the zero value or "control", in other words it is not more or less and is defined by an exposure value. As I said in my previous post, whether the photographer chooses to over or under expose is their choice and ironically the terms over and under indicates there is an "precise" exposure for the given value of light. Not withstanding the caveats of reflected light metering.

At any rate, back to the OP's topic. Grey cards are helpful in reflected light readings if one is attempting to avoid the reflective influence other colours may have on the cameras meter. Incident light meters are one way to measure the light falling on the subject and for the most part eliminate the colour bias of reflected light. So, one could buy a quality hand held light meter that does incident and have a grey card for times they wish to use the spot metering function of the built in meter. The caveat is, make sure you understand fully the proper technique in doing a camera meter reading.

 

[smoke665]

n a word, no. The quantity of the light on the subject has a specific value, it is this exposure value that is the zero value or "control", in other words it is not more or less and is defined by an exposure value. As I said in my previous post, whether the photographer chooses to over or under expose is their choice and ironically the terms over and under indicates there is an "precise" exposure for the given value of light. Not withstanding the caveats of reflected light metering.

I guess we will have to agree to disagree on the term "precise", as in my mind "precise" would take into consideration all "given value of the light", which due to equipment limitations is not possible to capture. Instead of some hypothetical fixed point, you have a floating variable that based on everything already discussed sets the point of "proper exposure".

Incident light meters are one way to measure the light falling on the subject and for the most part eliminate the colour bias of reflected light. So, one could buy a quality hand held light meter that does incident and have a grey card for times they wish to use the spot metering function of the built in meter. The caveat is, make sure you understand fully the proper technique in doing a camera meter reading.

For me I find it more consistent to use a handheld meter when shooting portraits. Having the ability to switch between reflective and incident is not something possible in camera. I'm a big fan Dean Collins and Chromazones, for backgrounds because of it's repeatability.

The caveat is, make sure you understand fully the proper technique in doing a camera meter reading. Most definitely!! Not only where to meter, but to also realize that in portrait photography skin reflectivity can vary greatly with pigmentation. I struggle the most with African American, as the color can vary from a deep black that sucks up light like a black hole to a rich honey that will blow out the highlights.

 

[JBPhotog]

I guess we will have to agree to disagree on the term "precise", as in my mind "precise" would take into consideration all "given value of the light", which due to equipment limitations is not possible to capture. Instead of some hypothetical fixed point, you have a floating variable that based on everything already discussed sets the point of "proper exposure".

The term "precise" has a quantitative value and essentially means recording the exposure for that ISO at the density which correlates to an exposure that is neither over or under exposed. For those of us who have used a densitometer this is an understandable concept and was essential in the calibration of a light meter back in the film days. Today's measurement tools are achieved by a known calibrated target and software analysis.

You can choose to disagree but science is science and should not be conflated with the photographers interpretation of exposure and/or what they are exposing for. Additionally, the OP was inquiring as to the purpose of a grey card to determine exposure which I think has been covered.

 

[Strodav]

IIRC, Kodak also stamped the date of production on the packaging of their grey cards so if you are using one from the 1980's don't expect it to still be 18% grey or for that matter neutral in its RGB values, over time the coating fades thus making it unreliable. My Sekonic Exposure Profile Target II comes in a black opaque sleeve to protect it from unnecessary fading and instructs the owner not to touch the surface and keep it stored properly.

Isn't the concept of a "precise exposure", also ambiguous? As you say the DR of the scene vs the capability of the sensor limit your exposure, but so does the capability of the medium of display.

In a word, no. The quantity of the light on the subject has a specific value, it is this exposure value that is the zero value or "control", in other words it is not more or less and is defined by an exposure value. As I said in my previous post, whether the photographer chooses to over or under expose is their choice and ironically the terms over and under indicates there is an "precise" exposure for the given value of light. Not withstanding the caveats of reflected light metering.

At any rate, back to the OP's topic. Grey cards are helpful in reflected light readings if one is attempting to avoid the reflective influence other colours may have on the cameras meter. Incident light meters are one way to measure the light falling on the subject and for the most part eliminate the colour bias of reflected light. So, one could buy a quality hand held light meter that does incident and have a grey card for times they wish to use the spot metering function of the built in meter. The caveat is, make sure you understand fully the proper technique in doing a camera meter reading.

Just for the hell of it I took my X-Rite Spectrophotometer off the shelf, calibrated it then took some Lab readings of my very old Kodak 18% gray cards. I was amazed by how accurate they still are over all these years. Took several readings and the L values all ranged between 48.5 and 48.9 (49 is optimal) and all of the a and b values were much less than a delta E from neutral. Amazing!

After reading through the posts I have come to the conclusion that there is no useful definition of “precise exposure”. So to me, “precise exposure” is that exposure the photographer chooses to obtain the artistic result they are looking for.

 

[JBPhotog]

After reading through the posts I have come to the conclusion that there is no useful definition of “precise exposure”. So to me, “precise exposure” is that exposure the photographer chooses to obtain the artistic result they are looking for.

I think I gave you the definition of "precise exposure". The photographer can choose to deviate and expose for what ever they want but that is inducing their bias for the look they are seeking, it doesn't change the fact that a specific amount of light is falling on the scene.