How to use a Grey Card

[Oldboy]

Same goes for anyone else who gets the urge. 

I try to keep my urges under control, thank you! 

[ABERS]

However taking a reading from the back of your hand at arms length always worked for me when working with film in an open air and rapidly changing light source situation.

I used to have problems with metering until I read a piece of advice from Victor Blackman in AP about 50 years ago. The advice was to meter from the palm of your hand and increase the exposure by one stop. The palm, not the back, he advised because palms don't tan as the backs of hands do. There is apparently a great degree of uniformity in the Caucasian palms of hands.

This is of course basically an incident light reading - as a grey card is.

Surely taking a reading of the light falling on to a subject is incident light reading, whereas that being reflected from anything e.g. a grey card, is a reflected reading.

All TTL metering is reflectied light metering, unless some whizz kid has invented some new gizmo!Incident light reading can only be done with a light meter.

Since I was usually taking candid portraits, most people's faces were a little weatherbeaten and the back of the hand worked fine. But that's being a little pendantic and I take your point about the palms.

[StephenBatey]

Incident light metering means measuring the light falling on the subject. All incident light measurements are carried out with a diffusing dome in place, and the meter is measuring the light that is coming from the dome, rather than the subject. It's transmitted, so it isn't the light directly falling on the subject (some will have been absorbed by the dome) but the point is that the dome averages out the light so that what you're measuring is directly related to the light falling on the subject.

When you use a uniform object of fixed reflection, you're doing exactly the same thing - taking a reading that is directly related to the incident light. Which is why I said it was basically the same thing. All you need to do is to apply an appropriate adjustment, which is what incident light meters do when the dome is in place.

You can use the indirect method when the light is too dim to get a reflected reading if you use a white card (or handkerchief) and just give more exposure (amount depending on what you use). This method certainly works in dim light if you don't have an incident light meter.

[ABERS]

If you embark on an incident light reading you have no need for a grey card.

Yes you need the diffusing the dome on the light meter to take the incident light reading. The meter, with the dome attached, is held close to the subject with the dome pointing towards the light source, therefore you are measuring the light falling on the subject, the incident light. The fact that the meter is calibrated to the diffusion properties of the dome doesn't make it a reflected reading.

The grey card is only used for a reflective reading, and is the direct opposite of incident reading. The dome is removed, the meter is pointed to the grey card and then reads the reflected light.

The two things are completely separate, but incident light readings are deemed to be more accurate for setting exposures, whilst grey card readings are purely an average exposure settings.

My old Weston Euromaster served me well for many years and still lives in my bits and bobs drawer.

[Alfonso_Frisk]

Since I started film a couple months ago I now have a Gossen Light Meter.
Metering was one thing I have struggled with in both formats, but I can say now I am getting better results by using the Gossen and ignoring the camera meter especially when I have old manual lenses on the Digi bodies.

[StephenBatey]

If you embark on an incident light reading you have no need for a grey card.

That's true; but the essential difference between incident and reflected readings is that the former gives a direct measure of the amount of light falling on the subject, and the latter the amount of light reflected back from it. In the case of general reflected light readings, this means that if you measure the light reflected from a predominantly dark subject, there's less light than if the subject is predominantly light.

Incident light measurement only means that you measure the amount of light falling on the subject, and whether you put a white plastic dome in the light path or a piece of card is neither here nor there. Yes, incident light meters have plastic domes; but they could equally well have used a separate card (grey or otherwise) for all that it matters. So long as what you are measuring is subject independent, it's effectively an incident light measurement. Which is all that I said. By measuring the light reflected from a subject of known reflectance, you are effectively measuring the light incident on the subject because the amount reflected is directly proportional to the incident light. A white dome will reduce the amount of light, so you're still not actually measuring the "neat" amount of light falling - you're still measuring a quantitiy that is directly proportional to the incident light but is not identical to it.

Incident light guards against overexposed highlights, which is the killer with digital and slide film; but for various reasons (to give them would swell this post far too much) it can result in underexposure (which is true even with digital and slide films) and isn't the best method to use with negative films where underexposure is the thing to avoid. The most accurate method is spot metering, which is a variant of a reflected light measurement.

To adequately go into all this would require a lot more space than is available in a forum post, and cover a lot of more or less technical background info.

[ABERS]

If you embark on an incident light reading you have no need for a grey card.

That's true; but the essential difference between incident and reflected readings is that the former gives a direct measure of the amount of light falling on the subject, and the latter the amount of light reflected back from it.

Without the risk of becoming repetitious that's what I said in the first place. You're assertion in your first post was that taking a reading from a grey card was an incident light reading.

Quote, "This is of course basically an incident light reading - as a grey card is."

Subject closed, before we bore the pants off everybody. 

[StephenBatey]

OK, my last post on the matter. I still stand by the assertion that if you measure the light reflected from a subject of known reflectance, the reading you get is directly proportional to the amount of light falling on the subject. The reading you get using an incident light meter and dome is also directly proportional to the amount of light falling on the subject. The only difference is that the constant needed to convert is directly built in to an incident light reading, and you may have to apply it with a card.

A reflected light reading when the meter is pointed towards the subject gives a value that depends on the incident light and the subject reflectance. Measuring from a uniform card eliminates the variable of subject reflectance and hence depends on the incident light alone.

I still regard a measurement that depends only on the light incident as an incident light reading. If you define an incident reading according to the method used (rather than what you're measuring) then naturally we'll never agree.

[Andrew]

The card maybe grey - but this thread is anything but 

Now, what can i write about an old fashioned cable release as opposed to these modern cabled computers that you plug into a digital camera (though not an X-Pro 1  )

[StephenBatey]

Well, the older style cable release depends on a physical pressure and contact with the shutter release (I use one on my cameras) and hence, depending on the flexibility of the cable could potentially transmit a vibration to the camera. The necessity for a physical link can also limit accessibility and distance (although the bulb releases can have a long range).

An electrical release (such as can be used with my OM system when a winder or motor drive is attached) reduces the possibility of movement.

And a truly remote release removes all possibility of movement from the attachment of a device to the shutter, and allows triggering the camera from a distance - inside the house to operate a camera trained on the bird table for example. This could also be achieved in the old days with the OM30, which could be set to release the shutter when something came into focus without anyone needing to be there. Possibly the ultimate in remote releases, with the exception of camera that can be triggered by the subject breaking an IR beam.

Well, that's my suggestion of the sort of thing you could write 

[Oldboy]

Well, the older style cable release depends on a physical pressure and contact with the shutter release (I use one on my cameras) and hence, depending on the flexibility of the cable could potentially transmit a vibration to the camera. The necessity for a physical link can also limit accessibility and distance (although the bulb releases can have a long range).

An electrical release (such as can be used with my OM system when a winder or motor drive is attached) reduces the possibility of movement.

And a truly remote release removes all possibility of movement from the attachment of a device to the shutter, and allows triggering the camera from a distance - inside the house to operate a camera trained on the bird table for example. This could also be achieved in the old days with the OM30, which could be set to release the shutter when something came into focus without anyone needing to be there. Possibly the ultimate in remote releases, with the exception of camera that can be triggered by the subject breaking an IR beam.

Well, that's my suggestion of the sort of thing you could write 

If you are really clever you get the wildlife to do it for you. 

http://www.dailymail.co.uk/news/article-2247690/Curious-black-bear-takes-photography-hijacking-wildlife-snappers-camera.html   

[StephenBatey]

But you'd need to educate them to use a cable release or remote trigger first...

[Mick]

I noticed in this video it mentions two different grey cards for two different jobs, one for exposure / meter readings, and one for white balance.

[StephenBatey]

Probably because correcting the white balance requires the card to be free of metamerism and setting the exposure doesn't. Hence, you need a grey card (or white card) that has a uniform spectral response to set the white balance. I have heard that the Kodak grey card isn't uniform, but I don't own one and I've tested one so this is purely second hand information.