This is a tutorial I wrote for my camera club's newsletter.
A grey card can be used to do two things:
1. Set a white balance
2. Set proper exposure
First, what is a grey card? To state the obvious, it is a card, fold up reflector or even a sheet of paper that is the colour grey. Wikipedia has this to say:
A grey card is a flat object of a neutral grey colour that derives from a flat reflectance spectrum. A typical example is the Kodak R-27 set, which contains two 8x10" cards and one 4x5" card which have 18% reflectance across the visible spectrum, and a white reverse side which has 90% reflectance. Note that flat spectral reflectance is a stronger condition than simply appearing neutral; this flatness ensures that the card appears neutral under any illuminant.
Sounds very technical. The important parts of that statement are the 18% and flatness. In other word it is a flat (non-reflective) grey card.
Set a White Balance
There are two ways of doing this. You can set a custom white balance in the camera or you can use a reference photo to set the white balance in your editing software. Setting the white balance in the camera is the easiest because once you do it you are done for all photos until you change the white balance to another setting or the lighting conditions change. This method also appeals to those who like to get it right "in camera" and prefer to as little post processing as possible.
Setting White Balance in Your Camera
The details on how to do this will vary slightly by brand of camera and even model of camera in some cases. The basics all remain the same but consult your camera's manual for details.
1. Take a photograph of the grey card near to the subject you are photographing. Make sure the grey card is getting the same light as the subject. If a portrait it is common to have model hold the card in front of their face. Try to fill the frame with as much of the card as possible. This helps the camera's metering system.
2. Select the custom white balance on your camera (Canon often has a button on the right of the LCD, Nikon has the same on the left or can be a menu option on these and other cameras). Your camera will ask for a photograph to use setting the white balance. Select the image you took of the grey card.
3. Before taking another photograph, access the white balance settings on your camera and select the custom one. This will use the white balance set in the previous set.
4. Repeat the steps as lighting conditions change. Custom really means custom to the light conditions as you set them in the first photo. If the light moves or you move, change the white balance!
The last step is an important one, especially if you shoot jepgs. You must reset or change the white balance when the lighting conditions change. If you are shooting the same thing for several hours outside, the sun is going change position and change your lighting. If you move to a different location, you need to change the white balance again to match the lighting conditions there.
If you forget all is not lost because you can fix an incorrect white balance in your editing software, but that defeats the purpose of setting it in the first place. The warning for jpegs is because the white balance is harder to correct after in your editing software than it is for raw photos. It can still be done as long as the white balance is not too far off.
Setting the White Balance in your Editing Software
The way to do this in your editing software varies of course. I will cover Photoshop, Photoshop Elements and Lightroom.
Photoshop and Photoshop Elements
Photoshop uses Bridge and Elements uses the Organizer to catalogue your photographs. Open whichever you have and we will start from there.
1. Select the photograph with the grey card plus any others that are lit under the same lighting conditions.
2. Open all of these images into Adobe Camera Raw (if jpegs you can still do this be using the File Menu and Select "Open in Camera Raw" or Open As Raw, the actual menu option varies depending on your version of the software).
3. In ACR select the photo with the grey card in it. This photo should be visible in the main window.
4. Select all the other images by clicking the Select All button.
5. Select the White Balance tool (the eye dropper) icon from the menu bar.
6. Having the eyedropper tool selected, click on the grey card.
7. If they are raw files, continue on with any other adjustments you need to make in ACR. You can also make adjustments to jpegs in ACR as well.
8. Select Done to save the images or Open Images to do further editing in Photoshop or Elements.
This will have set the white balance for all of the selected photos.
Lightroom
In Lightroom the process is slightly different. We will start after you have imported the photos.
1. Open the photo with the grey card in the development module.
2. Select the White Balance tool (the eye dropper) from the Basic panel.
3. Click the eyedropper on the grey card in the photo. The white balance is now set.
4. Select all of the other photos that are lit with the same lighting conditions.
5. Select the Sync button at the bottom of the right hand series of panels.
6. Uncheck all of the boxes except the White Balance check box.
7. Click on the Synchronize button to apply the custom white balance on all of the selected photos.
Using a Grey Card to Set Proper Exposure
Grey cards, for being so simple, are a multi-purpose tool. Not only can you use it to set a proper white balance but you can use it to set a proper exposure as well. Often very bright scenes, such as snow, can fool the meter in the camera to underexpose. The opposite can also happen with a very dark scene leading to over exposure. A grey card can fix both.
1. Select a centre weighted or spot-metering mode on your camera (the name of this may vary from Canon to Nikon to Sony, etc).
2. Fill the frame with the grey card.
3. If using full manual mode you can adjust your aperture and shutter speed to get the correct exposure from the grey card.
Or
3. If, like most, you are using a semi-auto mode like Av (A) (aperture priority) or Tv (S) (time value or shutter priority) you use the exposure lock (usually a button marked with * ) on your camera when you point at the grey card. Check your camera's manual for full details for your camera.
If you are using manual mode of your camera you can recompose and take your photo. However, if you are using Av or Tv you will probably need to keep holding the Exposure Lock button while you recompose and take your photo.
A very comprehensive and useful posting. I appreciate the work it took. Thank you.
You are welcome. I thought I would share.
Nice one Don, thanks for that handy info. Would make a great article you know. ;) http://cameracraniums.com/forum/index.php?page=articles
How do I do that?
As a black and white photographer, I can't comment on the white balancing part. On the exposure, at the risk of stating the obvious, the card should be placed in the same lighting conditions as the subject. Additionally, unless Kodak have changed their recommendations, the card should be placed at a 45 degree angle to the illumination. This is because most (possibly all) meters are actually calibrated to a 12% reflectance, not 18%; and the change of angle reduces the reflectance.
I don't know if camera makers tell you what their meters are calibrated to; but in the case of at least some hand held meters the makers do release enough technical information for you to be able to calculate the value.
From memory, you can find details of how to calculate in "Way Beyond Monochrome", although it may just possibly be in Ctein's "Post Exposure". One of the two, anyway. But I suspect if you have a built in meter, the info may not be available.
Just as an aside, in 30+ years I've never seen anyone use a grey card, even though for many years one nestled in the bottom of my camera bag.
When out and about they are totally impracticable, in a studio and still life situation O.K.
If you must impose all sorts of manual tasks on yourself to produce a decently exposed image, and enjoy the intricacies of such imposition, all well and good.
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. That's when I worked with everything on 'manual'. 8)
That's all gone now, I just correct my faults in L/room. ::)
I can comfortably say there is one type of photography where a grey card is essential - under water photography using digitial cameras.
Given the way water affects the available light and colours at differing depths - it becomes very useful to set a custom white balance instead of adding bundles of filters, not least of which the grey card can also double up as a writing slate on the back side and easily fits in the pocket of a BCD (the part that makes you float or sink).
Since converting to, and committing to shooting in raw, I very much leave WB in auto and correct it all in LR5.
That is not to say that your work has been in vein - I know people who like to take their knowledge to the very basics of understanding an aspect of photography and such an article would be most welcome.
It was written because of a request of a club member. There were many people on our snow outing that had problems with white balance and exposure. Lots of blue or grey snow in the photos.
Quote from: donoreo on February 19, 2014, 01:26:34 PM
It was written because of a request of a club member. There were many people on our snow outing that had problems with white balance and exposure. Lots of blue or grey snow in the photos.
Exactly - very useful to a whole bunch of people :-[
Just not me and Abers :doh: That's the trouble with 'old farts' - you can forget why something was useful when you've worked so logn without it
My camera club has plenty of old farts :) The same questions get asked over and over because their hearing is going and they do not hear the questions! In fact just last week we had one member (husband of the most recent past President) pass away. Like many camera clubs our average age is "retired".
Quote from: ABERS on February 19, 2014, 09:23:00 AM
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.
Quote from: donoreo on February 19, 2014, 12:48:24 AM
How do I do that?
Don, down the right hand side of the home page you should see a user panel, similar to this, although you won't have quite so many options in it, you should see the write article links. You should be able to embed images if necessary, but you'll need to upload them somewhere. The article system is available to all members of CC, should anyone wish to write one (some).
If any of you guys want to add images for articles then I can give access to the test site, where there's another gallery running, and embed them from there.
There are no screen shots, my word paint a picture :uglystupid2: I think I have it created now.
Quote from: donoreo on February 19, 2014, 09:07:05 PM
There are no screen shots, my word paint a picture :uglystupid2: I think I have it created now.
Found it and approved it. Thanks for writing that, I'm sure some will find it very handy. :tup:
I have turned off the side panels when viewing your article. As you'll also notice any article created by the members is also added automatically to the Article index. (http://cameracraniums.com/forum/index.php?page=articles)
Feel free to add more if you wish. Same goes for anyone else who gets the urge. ;)
Quote from: Mick on February 19, 2014, 09:27:03 PM
Same goes for anyone else who gets the urge. ;)
I try to keep my urges under control, thank you! :-[ :dance:
Quote from: StephenBatey on February 19, 2014, 08:07:01 PM
Quote from: ABERS on February 19, 2014, 09:23:00 AM
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.
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.
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.
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.
Quote from: ABERS on February 20, 2014, 01:06:37 PM
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.
Quote from: StephenBatey on February 21, 2014, 12:38:52 AM
Quote from: ABERS on February 20, 2014, 01:06:37 PM
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. ;)
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.
The card maybe grey - but this thread is anything but :o
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 :tup: )
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 :)
Quote from: StephenBatey on February 22, 2014, 12:58:53 PM
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. :P
http://www.dailymail.co.uk/news/article-2247690/Curious-black-bear-takes-photography-hijacking-wildlife-snappers-camera.html :doh:
But you'd need to educate them to use a cable release or remote trigger first...
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.
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.