18% gray card

[ifurlong]

I have an 18% gray card, why do I have this and what do I do with it, I have a 10d, thanks, Ian

[robertwgross]

It's difficult to state why you have the card. Maybe you purchased it. I got one on the back cover of a photography book.

Theoretically, if your 10D is set up right, and if you shoot a clear photo of the gray card normally illuminated, then you should get a single spike on the histogram almost perfectly in the center. That will tell you that the exposure values are correct.

---Bob Gross---

[ifurlong]

I was kidding, I bought the card, but I have no idea what to do with it

[scottbergerphoto]

ifurlong wrote:
I have an 18% gray card, why do I have this and what do I do with it, I have a 10d, thanks, Ian
The theory behind using an 18% Grey card, is that if you properly expose a single tone in a picture, all the tones will be exposed properly(Zone System). You place the 18 % Grey Card in the picture you want to take, in the light that everything else will be in. You take your exposure reading using a spot meter or zooming in using your camera meter and a zoom lens, or built in spot metering, and set your exposure off the grey card. You then recompose the picture, take out the grey card and shoot. You can also take just a picture of the grey card in the light you will be using for your subject based on the reading off the Grey Card. Make sure the Grey Card fills the view finder. The result should be a histogram with a single peak in the center. If not, adjust your exposure to get it there. Kodak provides detailed instructions for free on how to use an 18% Grey Card. You actually have to make some minor adjustments to the reading off a grey card due to its reflectance being a little brighter then it needs to be. If you didn't get instructions with your card, go to www.Kodak.com and check out their free publications. Also Roger Cavanaugh and I just discussed this on the Talk About Photography Forum.
Scott

[DaveG]

ifurlong wrote:
I have an 18% gray card, why do I have this and what do I do with it, I have a 10d, thanks, Ian

All reflection meters think that the world is 18% grey. If you were to meter a black door the meter inside your camera thinks "This door is 18% grey but there's very little light on it." If you were photographing a white door the camera's meter thinks, "This is an 18% grey door with lots of light on it." If you adjusted the settings of your camera so in both cases the camera's meter indicated a correct exposure then you'd have two identical negatives, both that would be 18% grey.

This is the reason that if you are photographing snow and just follow the meter you'll get grey snow instead of white snow.

The grey card is designed to be placed in a scene and then you meter the card. Since it IS 18% grey you will get a genuine and accurate meter reading. Once you meter off of the grey card, you just ignore what the meter tells you from that point on.

Using a reflected meter reading off of a grey card should give you the same results as using an incident meter.

The other thing is that there has been a rumour that the camera manufacturers have shifted the 18% standard to something else. I have no idea if that new standard is 12% grey or 13 or 33%. I don't even know if it's true, but someone will so I thought that I'd get this disclaimer in now. ;-)

See I can joke around too!

[hmhm]

There are two "meters" in your DSLR. One meters exposure by measuring how much light is bouncing off the subject and back to your camera. If a lot of light comes back, it assumes that there's bright light, and it picks a "short" exposure. If only a little light comes back, it assumes that there's dim light, and it picks a long exposure. Of course if there's bright light but the camera is pointed at a dark subject, the meter will be fooled, and it will think that there's dim light, and it will pick an exposure that's too long. This is a problem with using a "reflective" meter, it's results depend on the subject having some "typical" reflective properties.

The other "meter" is your white-balance meter. It is also a reflective meter. It looks at the light that bounces back from the subject, and tries to determine the color of the ambient light. Of course, just as for exposure, this type of reflective metering is dependent on the reflective properties of the subject. White light bouncing off a yellow subject will fool the camera into believing that the ambient light is really yellow.

One cure for the ills of reflective metering is to instead use "incident metering", where you place a meter in front of the subject itself, and directly measure the light striking it. This requires an extra hand-held meter, and hand-held color meters are actually very expensive (and may not work as well as your camera's built-in white-balance system).

The other cure is to provide a subject that has exactly those "typical" reflective properties that the reflective meter expects, and place that subject in the same light that will be striking your real subject. This allows you to accurately measure the brightness and or color of the ambient light, and choose exposure and white-balance appropriately.

Note that while grey cards are typically 18% reflectivity, most internal meters actually expect around 12% reflectivity. The instructions that came with your grey card probably instruct you to choose an exposure that's about half a stop greater than what the meter chooses from the grey card. If you have a subject that is particularly bright or particularly dark, you might still want to adjust the exposure down or up (respectively) to push the subject closer to the middle of the dynamic range, to avoid losing detail.

If all this was too much verbiage, then the short answer is "you use it to do custom white-balance, check the CWB section in your camera's user manual".
-harry

[Roger_Cavanagh]

You can use it like this:

http://www.rogercavanagh.com/helpinfo/29_graycard.htm

And for white balance, instead of the white sheet of paper that the manual describes.

Regards,

[OutsideShooter]

It's difficult to state why you have the card. Maybe you purchased it. I got one on the back cover of a photography book.

Theoretically, if your 10D is set up right, and if you shoot a clear photo of the gray card normally illuminated, then you should get a single spike on the histogram almost perfectly in the center. That will tell you that the exposure values are correct.

---Bob Gross---

Good Gawd Almighty, thank you Bob. I don't know how often I have read articles which for one reason or another, call me slow, it didn't register. Thank you for making this SIMPLE!!! The histogram, of course!!!

Too far to the left & its underexposed, too far to the right & its overexposed. Dead center & its a perfect neutral exposure.

Statements like the following are what grate at my intention to get a quick & useful approach:

"How do I take the reading for a good exposure? You can place the 18% gray card next to the subject of interest. Zoom in with your lens (or go closer) and now focus the gray card, adjust your shutter speed such that the light meter indicates perfect exposure. Now remove the gray card, zoom out and recompose your frame with your cat or whatever it is, DO NOT CHANGE YOUR EXPOSURE SETTINGS (let the reading be the one that you took off from the gray card) and then shoot et voila you now have a better and most realistic colors and shades of the picture as opposed to the one that the stupid light-meter has decided for you."

I like your explanation much better Bob.


Rich

[gasrocks]

Here's my suggestion: Meter the gray card, then meter the palm of your hand. Compare the 2 readings. Your hand is probably 1/2 f/stop lighter, I'm guessing. Leave the card at home - they cost money and of they get dirty they give you false readings. I usually have my hand with me when I am out taking pix. Oh ya, keep your hands clean.

[PacAce]

Ummm, who are you guys talking to? ???





;) :lol: :D

[Hermeto]

Living in the Past, Jethro Tull.. ;)
Thanks for bringing up 3.5 years old topic.

[OutsideShooter]

To PaceAce & Hermeto, whoever decides to listen & So when does gray cards & white balance become unuseable after 3 years?

Honestly I really learned quickly from Bob Gross's statement. In fact I just got back from a Nez Pierce Indian shoot & I was able to adjust on the fly. I know to most of you perhaps that is not exactly a milestone, but to me, it is like hitting a home run in the 9th inning with the score 3-0 & bases loaded.

Now who can tell me where I can get a gray card at 18% on the cheap? Today I used the interior pull away flap in my LowePro bag, but that's noisy & a hassle to tear out each time.

[SingingSabre]

Informative narco-posting. I like this forum.

[jr_senator]

The other thing is that there has been a rumour that the camera manufacturers have shifted the 18% standard to something else. I have no idea if that new standard is 12% grey or 13 or 33%.

13%

[gasrocks]

Hermeto, I do not understand. I thought this was a place to help people, especially people new to photography. Not to find a snide way to say " you should know that already."

[OutsideShooter]

Informative narco-posting. I like this forum.

There seems to be a few ahead of me here. Care to explain narco-posting? Or do some just like to lurk & occassionally drop a brick? I was under the impression most here have an ounce or two of compassion & helpful advice. This was why when we were all little children, the Teachers used to tell us "There are no stupid questions".

I don't see that paradigm changing none too soon. So again, Care to explain narco-posting?

BTW, thank you gasrocks.

[Hermeto]

Hermeto, I do not understand. I thought this was a place to help people, especially people new to photography. Not to find a snide way to say " you should know that already."

gasrock, helping people new to photography is fine, but helping them after more than 3 years doesn’t make much sense - if nothing else than for the sole reason that they are not new to photography any more..

Besides, I never said ‘you should know that already’, that is entirely your presumption.

[Hermeto]

To PaceAce & Hermeto, whoever decides to listen & So when does gray cards & white balance become unuseable after 3 years?

Honestly I really learned quickly from Bob Gross's statement. In fact I just got back from a Nez Pierce Indian shoot & I was able to adjust on the fly. I know to most of you perhaps that is not exactly a milestone, but to me, it is like hitting a home run in the 9th inning with the score 3-0 & bases loaded.

Now who can tell me where I can get a gray card at 18% on the cheap? Today I used the interior pull away flap in my LowePro bag, but that's noisy & a hassle to tear out each time.


Take a look here:

http://www.rawworkflow.com/products/whibal/index.html

[SingingSabre]

I don't see that paradigm changing none too soon. So again, Care to explain narco-posting?
Narco-posting...bringing back old threads from the dead. It's not a bad thing when it's a helpful thread like this.

[OutsideShooter]

Thank you Singing Sabre

[cbock]

you know...i learned something from this thread. and, quite frankly, it's a breath of fresh-air to have a topic updated in a single thread instead of searching thru 20 different threads on the same topic.

[jr_senator]

you know...i learned something from this thread. and, quite frankly, it's a breath of fresh-air to have a topic updated in a single thread instead of searching thru 20 different threads on the same topic.

And fresh insight.

[PhotosGuy]

Here's my suggestion: Meter the gray card, then meter the palm of your hand. Compare the 2 readings. Your hand is probably 1/2 f/stop lighter, I'm guessing. Leave the card at home - they cost money and of they get dirty they give you false readings. More on that:
Every highlight may not be one that you need to keep, so I need to decide what is most important in each shot. With cars, I prefer to start with a white "white", & let overly bright reflections blow out.
Need an exposure crutch? (http://photography-on-the.net/forum/showthread.php?t=89123)

[CyberDyneSystems]

Search tools are your friend, and it can bring up great old threads like this one.


Glad to see an informative thread make a come back.. and I miss some of the names from 2003.. it's like seeing old friends :)

[peterR]

These tutorial videos Whibal (http://www.whibalhost.com/_Tutorials/WhiBal/01/index.html) are very good in explaining the principle.

See if this helps.