Can someone explain the concept of metering from the palm of your hand and how this is different to using a grey card. I have used the grey card and hopefully have gotten correct results, but when I have tried metering off the palm of my hand, the RGB numbers differ immensely. I am probably palm metering incorrectly but I don't understand how this works. Any help would be much appreciated.
Palm Metering
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foggy4ever
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I've only heard of using the grey card for white balance not metering.
EdBray
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Metering from your palm will usually be between +2/3 and +1 stop brighter than that from a grey card. So to get the correct balance you would have to overexpose by that amount.
The first thing you should do is calibrate your hand against a known grey card with your camera meter and then the exposure difference will be your normal compensation.
The first thing you should do is calibrate your hand against a known grey card with your camera meter and then the exposure difference will be your normal compensation.
EdBray
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It's actually the other way around, Grey Cards are designed for metering, unless specifically noted they are not necessary a neutral gray so are not always correct for white balance settings.
foggy4ever
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Thanks Ed 
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My Weston meter has an indicator position specifically for metering from the palm of your hand. It is one stop different to a grey card or average scene setting.
Steve.
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mrtoad
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it will give you skin tone readings...
i use it as a check on what my camera says and where i spot the meter
i think grey card is more average
HoppyUK
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Metering off a grey card, or the palm of your hand, or a white card/shirt/blouse, or off any object of known brightness, is a form of incident light metering.
Basically, if you know the brightness of the object, then you also know the brightness of the light falling on it and from that can calculate a very accurate exposure setting. The advantage of a calibrated 18% grey card is that you can meter off it and set the exposure directly without any compensation. (You can also use it for white balance.) The advantage of using the palm of your hand is that you always have it, well, to hand, and once you've calibrated it, it doesn't change so long as you wash it now and then.
If you use the palm of your hand, you should usually increase the exposure indicated by 1.3 stops. Off a clean white card, it is usually about 2.5-3 stops.
Basically, if you know the brightness of the object, then you also know the brightness of the light falling on it and from that can calculate a very accurate exposure setting. The advantage of a calibrated 18% grey card is that you can meter off it and set the exposure directly without any compensation. (You can also use it for white balance.) The advantage of using the palm of your hand is that you always have it, well, to hand, and once you've calibrated it, it doesn't change so long as you wash it now and then.
If you use the palm of your hand, you should usually increase the exposure indicated by 1.3 stops. Off a clean white card, it is usually about 2.5-3 stops.
webbEvents
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I had to compare readings using a palm as part of my NVQ4 course. A while ago now, but IIRC scrunching up your hand so the lines were more pronounced and had some shadow on them gave a more acurate result. It was a few years ago now and its not a technique that I feel I need to use, so can't be more certain than that.
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HoppyUK
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Where are you in East Mids? I'm Peterborough. That's another post for you
Here's one reason why palm metering is useful.
An incident light meter reading, which is what this effectively is, measures the brightness of the light - which is what matters. A reflected light reading, ie normal in-camera metering, measures the brightness of the subject - which usually doesn't matter. Classic example of bride and groom - meter off the bride in white and you'll get a high reading, meter off the groom in black and you'll get a low reading whereas correct exposure is the same for both and will be somewhere between the two (mid grey). That's because the light falling on both subjects is the same, and an incident light reading measures that light.
Here's and example where palm reading is really useful. Shooting a moving subject like children running around the garden, the correct exposure needed stays the same so long as the sunlight stays the same, but if you use a normal reflected light meter reading it will vary as they move against different backgrounds - grass, dark trees, sky, whatever. You don't want the exposure to change so you would set it in manual.
However, if it's a cloudy and windy day the sunlight is going to change and you need to keep a check on that by referring to a subject that is a constant and known brightness, ie the palm of your hand. That way, you can adjust the exposure according to the lighting conditions, and not when the brightness of the background changes.
If you watch professionals at a motor racing track, you will see them frequently pointing the camera down at the tarmac, or on to an area of grass. What they are doing is checking their camera settings against a subject of known brightness in case the light has changed. (They would probably use the palm of their hands, but given the size of the lenses they use, they would need an arm ten feet long
)
EdBray
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Where are you in East Mids? I'm Peterborough. That's another post for you
Here's one reason why palm metering is useful.
An incident light meter reading, which is what this effectively is, measures the brightness of the light - which is what matters. A reflected light reading, ie normal in-camera metering, measures the brightness of the subject - which usually doesn't matter. Classic example of bride and groom - meter off the bride in white and you'll get a high reading, meter off the groom in black and you'll get a low reading whereas correct exposure is the same for both and will be somewhere between the two (mid grey). That's because the light falling on both subjects is the same, and an incident light reading measures that light.
Here's and example where palm reading is really useful. Shooting a moving subject like children running around the garden, the correct exposure needed stays the same so long as the sunlight stays the same, but if you use a normal reflected light meter reading it will vary as they move against different backgrounds - grass, dark trees, sky, whatever. You don't want the exposure to change so you would set it in manual.
However, if it's a cloudy and windy day the sunlight is going to change and you need to keep a check on that by referring to a subject that is a constant and known brightness, ie the palm of your hand. That way, you can adjust the exposure according to the lighting conditions, and not when the brightness of the background changes.
If you watch professionals at a motor racing track, you will see them frequently pointing the camera down at the tarmac, or on to an area of grass. What they are doing is checking their camera settings against a subject of known brightness in case the light has changed. (They would probably use the palm of their hands, but given the size of the lenses they use, they would need an arm ten feet long
Sorry Hoppy, that is wrong, the light measured from the palm is still reflected light just as it would be from a grey card, it is just another 'known value' and can be referenced against.
Incident light is measured by the use of a diffuser to average the light falling onto a subject from the subjects position.
webbEvents
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cheers Hoppy, up a bit from you in Grantham. Usually meter from the grass at airshows.....
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HoppyUK
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I beg to differ Ed
What is the difference between an incident light reading using a diffuser, and one taken from a reflective surface of known reflectance? There is none.An incident reading is a measure of the light falling on the subject. If you know the reflectance of the metering surface, or know the density of the diffusing material, you can measure it either way.
You can take either kind of reading from the subject position if that is critical.
'Palm-Metering'...lol
Something I used to do about 30 years ago - along with pointing the camera at a patch of grass nearby in the same light as the subject (Substitution Reading for want of a Posh Term). Works fine as long as you do actually make sure the 'palm' or grass is in the same light as the subject...
Since the introduction of Nikon's Matrix metering, I've had very few issues with in-camera metering from the scene I'm shooting - those minor niggles that do occur are - or have been - overcome by familiarity with the kit and lots of practice/experience...
Something I used to do about 30 years ago - along with pointing the camera at a patch of grass nearby in the same light as the subject (Substitution Reading for want of a Posh Term). Works fine as long as you do actually make sure the 'palm' or grass is in the same light as the subject...
Since the introduction of Nikon's Matrix metering, I've had very few issues with in-camera metering from the scene I'm shooting - those minor niggles that do occur are - or have been - overcome by familiarity with the kit and lots of practice/experience...