Cameranoobie
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First, does it need to be 50%? Can it be 35 or 18%?
Second, how do you go about this?
TIA.
Second, how do you go about this?
TIA.
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How do you set exposure on a camera with a 50% grey card?
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JuanVillarreal
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First of all, if you do not want to do some calculations, you are better off with a 18% gray card.
You should put your card in the place where your subject will be when the photo is taken, and oriented so that the surface of the card is parallell to whatever surface in your subject you consider the main surface. The card should be big enough to cover the sensitive area of the exposure meter. This could be a small portion on the center if you set up for spotmetering, or it could have to be a large part of the image area if you are set up for matrix metering.
Then you can set the camera for manual exposure and adjust, or lock the measurement pushing the trigger halfway or whatever your camera allows, remove the card and press the trigger all the way.
As camera exposure meters try to make the average exposure of the frame 18% guessing that most subjects have a reflectance near 18%, when the card is used, then the meter will be right, the subject is actually 18% reflective and the photo should be correctly exposed.
You should put your card in the place where your subject will be when the photo is taken, and oriented so that the surface of the card is parallell to whatever surface in your subject you consider the main surface. The card should be big enough to cover the sensitive area of the exposure meter. This could be a small portion on the center if you set up for spotmetering, or it could have to be a large part of the image area if you are set up for matrix metering.
Then you can set the camera for manual exposure and adjust, or lock the measurement pushing the trigger halfway or whatever your camera allows, remove the card and press the trigger all the way.
As camera exposure meters try to make the average exposure of the frame 18% guessing that most subjects have a reflectance near 18%, when the card is used, then the meter will be right, the subject is actually 18% reflective and the photo should be correctly exposed.
Moti
Veteran Member
The sndard grey card is 18% if you'll use a 50% gray card to measure the light, chances are that your photos will come out overexpose, unless you use compensation.
I use a gray card for WB only and not for light measuring. If I need to be very precise, I'll always prefer to use an incident light meter rather than reflected measurement from a card.
Moti
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Mark S Abeln
Forum Pro
It's an oddity of human physiology that a gray card that reflects about 18% of light, appears, to the human eye, to be about halfway between white and black. A card that truly reflects 50% of the lighr would appear to be merely a very pale gray.
Eyes work this way because they are adapted to operate under a vast range of brightness. And so, cameras attempt to mimic human vision, to a degree.
However, it might be best not to use a gray card for exposure (while it is still a great idea to use a gray card to set your cameras white balance). A better method is to determine what are the most significant highlights and shadows in your scene, and adjust exposure so that these are preserved; you might have to change contrast in the camera or on the computer to get a good tonality in your final image.
If we assume that an in-camera meter reading of an 18% grey card will give correct exposure of a subject in the same light (which is not a proper assumption), then a reading off a 36% grey card will result in an exposure which is 1 stop underexposed (again, assuming that the meter in the camera is actually calibrated to 18% which may not be the case). This can be managed in two ways: use the exposure compensation adjustment to increase exposure by 1 stop or put the camera in manual exposure mode and increase exposure by 1 stop either by opening the aperture or increasing the exposure time.
The problem with using grey cards is that their reflectance can change (with age or dirt) and that they can be tilted towards 'glare' angle which will give an incorrect reading. If you favor grey card metering, consider using an incident light meter (perhaps with a flat disc receptor) -- and then remember to factor in the actual transmission of the lens, T-stop, and any extension factor.
In the old days, the caucasians among us would use the palm of their hands as a 'grey card' and open up one stop to get a Zone 6 placement of exposure. Assuming that the reflectance of ones palm was always the same, one could make a similar 'calibration' for any skin color.
As for a 50% grey card -- what would it be 50% of? Only a mirror reflects 100% of the light falling on it theoretically -- so in essence, you'd be reading the surface of the light source. A good experiment is to take a piece of glossy printing paper, a piece of matte printing paper, a piece of plane paper and a piece of toilet paper and see what sort of exposures you need to reproduce their values accurately. You may find that what looks right on your monitor isn't the same as what appears in your prints.
a_c_skinner
Forum Pro
The idea of a grey card is to allow you to expose correctly with a reflected light reading from the card even if the object is unusually bright or dark. The other approach is to measure the incident light. For an 18% test object (card or folding reflector type) the idea is you place the card in the same light as the scene and use the exposure that gives. I'm not aware of cards other than 18% being widely used.
This is really for day to day photography now obsolete. Yes, I've tried them when I took slide film but I've given them up. In truth I did just as well with some rule of thumb corrections to a normal reflected reading.
Digital is a new process. Anything other than simply allowing the camera to set the exposure automatically involves extra steps and if you are going to that trouble (and I always do) the rational thing is to use the camera histograms to refine the exposure. There are theoretical reasons why this is not right for both RAW and JPG simultaneously but they will only rarely make any visible difference to the final result at display time. If the subject is suitable bracketing exposure is easy nowadays and was a common technique (as was a Polaroid test shot) for commercial snappers in film days despite the cost because there isn't a magic bullet for exposure.
As elsewhere there is a use for these cards in setting WB either at taking or in processing.
This is really for day to day photography now obsolete. Yes, I've tried them when I took slide film but I've given them up. In truth I did just as well with some rule of thumb corrections to a normal reflected reading.
Digital is a new process. Anything other than simply allowing the camera to set the exposure automatically involves extra steps and if you are going to that trouble (and I always do) the rational thing is to use the camera histograms to refine the exposure. There are theoretical reasons why this is not right for both RAW and JPG simultaneously but they will only rarely make any visible difference to the final result at display time. If the subject is suitable bracketing exposure is easy nowadays and was a common technique (as was a Polaroid test shot) for commercial snappers in film days despite the cost because there isn't a magic bullet for exposure.
As elsewhere there is a use for these cards in setting WB either at taking or in processing.
A grey card can be useful when you are photographing subjects such as drawings, paintings, textiles or wallpaper designs.
For ordinary 3D subjects, the usual matrix metering in modern cameras works well. If in doubt, bracket, or check the histograms.
For ordinary 3D subjects, the usual matrix metering in modern cameras works well. If in doubt, bracket, or check the histograms.
M
Mark B.
Guest
Who sells a 50% grey card, and if so why would you want to go through that hassle? 18% grey cards are common enough that there's absolutely no reason to create extra work for yourself.
henryp
Veteran Member
Don't you mean underexposed. If you try to expose for a 50% gray (grey} card without compensating for the fact that it is 50%, your photos will come out underexposed.
a_c_skinner
Forum Pro
Over, I think. The card will be darker than an 18% one, so the camera will expose more to make it look 18%.
No one uses 50%, I think, it was a misprint by the OP I suspect.
No one uses 50%, I think, it was a misprint by the OP I suspect.
Easy. You experiment.
A 50℅ grey card should give images that are over exposed. Since the standard is either 12% or 18%, depending on who you talk to.
So experiment with exposure compensation to under expose until you get the image right.
a_c_skinner
Forum Pro
It is actually easier. Just forget about this. Put it to the back of your mind except for very specialised applications, perhaps art work. Even then exposing RAW files using the histograms will leave you with files that correct in processing. This technique is history for almost everyone. Honestly
fishy wishy
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Well... would you say the same for incident light metering. Someone is asking in another form about incident light metering for portraits. People may be wondering why spotmetering the face isn't enough.
GeraldW
Veteran Member
Well, almost everyone. It gives me a nice standardized target for comparing light meters and cameras's meters. So I still use my gray card if a camera seems to be giving me odd results.
Most people don't understand how to use a meter properly whether incident or spot. Incident meters usually have hemispherical domes which intergrate all the sources into one general reading which is convenient but doesn't provide information as to the intensity of individual sources which may be contributing to the overall illumination nor should it be used for determining ratios. For that, some meters provide a flat disk which is aimed at the indivual light sources (usually with a hand shielding the disk from other sources).
Meters that read reflected light over a large area average the illumination coming off the subject -- not the best way to go, though some of them have/had the ability to measure the brightest and darkest areas, display their values and also average them or bias toward highlight or shadow. Spot meters read reflected light; some meters could be aimed at a highlight and shadow and average the readings; one could also take a reading off either a highlight or a shadow and get an exposure reading based on that. Of course some highlights are specular and some shadows have no detail at all -- so knowing where to point the meter is important.
It's all well and good to use a digital camera the way we used to use Polaroids -- but as with the Polaroids, it's not a perfect equivalent to what ends up as the RAW file -- since the image on the LCD is a jpg. Histograms are better but again, most people don't understand what they portray:
"A histogram illustrates how pixels in an image are distributed by graphing the number of pixels at each color intensity level."
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For those who use any form of card as an exposure target, readings often vary with the angle at which the card is held and is therefore less consistent than an ambient light meter (properly used).
One advantage of using the in-camera (TTL) meter is that it takes into account the actual light transmission of the lens (T-stop vs F stop), light loss when shooting closer than infinity, filter factors (sometimes) and, with the Sony SLT cameras, the light loss due to the pellicle. ISO (International Standardization Organization) 'speeds' can vary by brand and from camera to camera -- so without testing, one can expect significant variations.
a_c_skinner
Forum Pro
In an age with immediate access to a test exposure I honestly don't see why anything is better than examining the finished result - usually using the camera histograms. I know these have shortcomings but it isn't as if incident metering or using a gray card (in effect incident metering) are foolproof or give ex cathedra results, I just don't see the advantage over examining the files as taken, either means a comparable amount of extra work.
Has the OP has been a victim of internet overcomplication?
Has the OP has been a victim of internet overcomplication?
CharlesB58
Forum Pro
a_c_skinner
Forum Pro
Sorry, yes. Correct.
Iliah Borg
Forum Pro
And more. Meter calibrations may vary. They may even vary with ISO speed setting on a camera. Camera firmware is calibrated in such a way that anything under the meter will result in 18% (approximately sRGB 118) in out of camera JPEG.
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