Grey Cards and White Balance and zones

[TrishMac]

Hello Everyone,

I need help!!!! I am doing an online course and trying to work out the details and just not getting it. Our assignment is to test our camera by doing a zone test and work out the limits of our camera. I have done the grey card test and come up with the numbers from 0 0 0 through to 255 255 255, however I am not seeing the point. I guess this is one of the disadvantages of the digital era where everything can be done post production and knowing these details is not as important as it used to be.
My questions are: (apologies...here is where the stupid questions come )
1. Should I be metering the camera for every session?
2. How do I meter the camera, should I have it on Custom White Balance to meter?
3. From the numbers (of the grey card test) how do I tell if my camera likes the darks or the lights better?
Just waiting for the light bulb to come on....any second now!!
I have a Canon 7d. Please correct me if I am wrong...this test is to get correct exposure every time by knowing where the camera sits in the range and then adjusting the settings accordingly.
I really, really want to have a good understanding of the camera, gosh, who would have thought there was this much to it!
Thank you, thank you in advance and hoping someone can get this through to me!!
Regards
Trish

[Colin Southern]

Hi Trish,

I promise to do my best to help - but - I'm not sure I totally understand your questions yet.

First thing I want to point out though is that metering and white balancing are two seperate thngs with only a (very) small overlap. I think the majority of your questions seem to revolve around the former rather than the latter, so shall we start with exposure first?

We've had a few discussions about this in the past - would you be so kind as to have a read through this thread to see if it helps gel a few things into place?

What is the best method for learning how to expose photos correctly?

Talk soon!

[TrishMac]

Hi Colin,
What a great thread, thank you, I will also PDF it and keep it for handy reference!! After reading the thread, I think my problem is/was that I don't know how to actually set up the grey card, meter it and set the camera.
And I think I have finally worked out how to use the grey card to meter. If I take a shot of the grey card (on spot metering) and then go into the custom WB and "use WB data from this image for Custom WB" and then take my photo's, the WB should be set to the correct light conditions? Is that right?
With the zone test we have to do, set the camera on manual, using the grey card and work out the dynamic range from Zone 0 through to ...zone IX, creating our own zone ruler. After having read the previous post, it is all starting to make a little more sense to me now, so I will read through my notes and start again!
PS We were in Nelson earlier in the year and then spent 2 weeks over the hill in Takaka, what a great place in the world you live! My next stop is your website!
Thanks
Trish

[rachanne]

Hello Everyone,

I need help!!!! I am doing an online course and trying to work out the details and just not getting it. Our assignment is to test our camera by doing a zone test and work out the limits of our camera. I have done the grey card test and come up with the numbers from 0 0 0 through to 255 255 255, however I am not seeing the point. I guess this is one of the disadvantages of the digital era where everything can be done post production and knowing these details is not as important as it used to be.
My questions are: (apologies...here is where the stupid questions come )
1. Should I be metering the camera for every session?
2. How do I meter the camera, should I have it on Custom White Balance to meter?
3. From the numbers (of the grey card test) how do I tell if my camera likes the darks or the lights better?
Just waiting for the light bulb to come on....any second now!!
I have a Canon 7d. Please correct me if I am wrong...this test is to get correct exposure every time by knowing where the camera sits in the range and then adjusting the settings accordingly.
I really, really want to have a good understanding of the camera, gosh, who would have thought there was this much to it!
Thank you, thank you in advance and hoping someone can get this through to me!!
Regards
Trish

Hi Trish Im up to that very assignment now. I have all the same results with grey card at different iso 's 100 400 and 800.Im unsure if Im correct. How did you go? Please help some one as I am still getting used to my new dslr camera also.

[Graystar]

Hi Trish Im up to that very assignment now. I have all the same results with grey card at different iso 's 100 400 and 800.Im unsure if Im correct. How did you go? Please help some one as I am still getting used to my new dslr camera also.

This thread is two years old, so I doubt Trish will respond.

What is this online course that you're taking? We'll need to see it in order to figure out the knowledge that you are supposed to either practice or ascertain from this exercise.

If you metered a gray card at different ISO values, got the same results every time, and are unsure if that's correct...then you haven't been taught how a reflective meter works. The quick answer is yes, you should have the same result. However, I can tell you right now that you've gained nothing from neither the exercise nor the answer I just gave.

The "try it and see what happens" method of learning is, in my opinion, the absolute worst way to learn photography. That's because there are too many things going on that you simply cannot see (such as the reason why all your results were the same.)

In another forum, someone asked how a meter worked and I wrote this response. I'll just copy and paste it here for you. But we really need more info before we can set you on the right path.


How does the in-camera light meter work?
A book could be written to answer your question! But I'll try to keep it short. You asked about three different things...basic metering principle, metering as related to metering mode, and the advanced operation of intelligent metering systems. So first...metering principle.

First a word on exposure. Exposure is always set for the light source. You can use a handheld light meter to meter the light source directly, and it will provide settings for your camera that will give correct exposure. Such a meter is called an Incident light meter. It works because the colors and tones of the objects in your scene do not affect exposure. Only a change in the light source will change your exposure settings.

Cameras use a Reflective meter. That means that it meters the light that is reflected from the scene itself. Now...white can reflect 90% of the light falling on the scene, while black may only reflect 5% of the light falling on the scene, but remember that there's only one "correct" exposure (based on the light source.) So how can the reflective meter give a correct reading?

It doesn't...it fakes it. First, the meter presumes that the world is gray...12.8% gray, in fact (that is, a surface that reflects 12.8% of the light that falls upon it.) If you want to see what 12.8% gray looks like then open a painting program, set your color to RGB 100, 100, 100, and fill the canvas with that color. That's 12.8% gray. (oh...do the same with RGB 118 to see 18% gray.)

Having presumed that the world is gray, the meter will now set exposure such that whatever it sees in front of it comes out as gray. So if you meter a white wall and take a picture, it comes out gray. Meter a black wall, and the picture comes out gray. Obviously, not a good result. So why does it work this way? Well, it turn out that if you take typical everyday scenes from life, average all the light and dark areas together, you end up with an average that's about 12.8% gray! So even though the reflective light meter is "faking it", it works fine for typical scenes of everyday life.

Now we can address metering modes. The Center Weighted metering mode was introduced back in 1967 with the Nikon F. It averages the entire scene, with an emphasis given to the center area. This is an old metering mode, and is not used very much today. The reasons are, Matrix performs full-frame metering a bit better than CW, and Spot metering provides far greater control over metering.

Spot metering meters a very small area. The idea here is to reduce the influence of the surrounding objects so that you can concentrate on the exposure of a single tone. But recall that I said that metering a white wall or a black wall will give you a gray picture. Obviously, the meter made an error...however, the error that the meter makes is constant and predictable. If you could learn the errors that the meter produces for various objects, and somehow compensate for those errors, then you can use the spot meter to set exposure accurately. This is where Exposure Compensation comes into play. Combined with knowledge of compensation values, the spot meter can be used to produce accurate exposure settings. For example, you can meter a light-skinned face, set EC to +1.0, and take the picture...exposure will be correct.
Snow, +2.3
Evergreen tree, -1.0
Healthy green grass or blue sky 45 degrees up, +0.0
18% gray card, +0.5

If you use this method, what will happen is that through experience, you will build a table of compensations in your head for the subject matter that you prefer to photograph. Once you have this knowledge and have mastered the skill of spot metering to set exposure, the benefit is that you can usually set exposure correctly the first time...no need to review your pictures and try again.

Matrix metering is a so-called intelligent metering mode. It is the "full-auto" of metering modes. If you don't want to be bothered with developing the skill of setting exposure, then just use Matrix metering. Matrix metering starts by evaluating the luminance and colors of the scene. Then it tries to match the scene to its database of over 30,000 scenes. If it finds a match in the database then the camera will apply the exposure compensation that some Nikon photographer thought was appropriate for such a scene. Snowy landscapes tend to be underexposed. So if you're photographing a snowy landscape, and your scene matches a snowy landscape scene in the Nikon database, then the camera will apply compensation to avoid the underexposure. This makes Matrix metering unpredictable by design, because you can never know what compensation the camera will decide to apply.

An 18% gray card is the traditional tool for setting exposure. Remember that the meter presumes that the world is gray. When the meter meters white, black, light-skin, evergreens, etc...you get an error in the reading. But if the meter meters something that is 12.8% gray, you get no error. This is the principle of using a gray card. You meter the gray card, and your exposure should be correct. Unfortunately, there are no 12.8% gray cards...only 18% gray cards. No one knows why, so don't ask (the true reasons are lost to history.) If you buy a Kodak 18% gray card, it will include instructions telling you to set exposure using the card and then increase exposure by +0.5 (which is the difference between 12.8% and 18% gray.) So you can still use an 18% gray card to set exposure.

I use my white-balance reference to set exposure. I have a Digital Gray Card by RM Imaging. It's a 4"x6" gray reference that is designed for setting white balance only. However, as with light-skin, evergreens, and snow, a little experimentation was all that was needed to determine a compensation value suitable for the WB card (which turned out to be around +1.3.) Now I can set white balance and exposure with the same card, which I carry in my back pocket.

[rpcrowe]

I have been a photographer for well over fifty years most of that time professionally. I have never worked with the zone system of exposure because it is too slow and laborous for my styles of shooting. Saying that, I also have never had any problems getting correct exposure whether I used an incident light meter, a hand-held reflective meter or the built-in camera meters...

Exposure has become even simpler with the advent of digital photography with inatsnt feedback...

As far as white balance goes, for the last year or so I have been using a a WhiBal card for getting the white balance within the ballpark. I like the WhiBal quite a bit but, really did not have any problem with white balance before I began using the WhiBal card. I always shoot in RAW and will most often use auto white balance with my Canon DSLR cameras.

BTW: Color balance is IMO absolutely most important when shooting products which must be reproduced in exactly correct colors. Color balance is also important when shooting faces but, there can be variations when shooting portraits. I aim for the most pleasant skin tones rather than the most accurate...

Michael Tapes WhiBal video tutorials are interesting...
http://whibalhost.com/_Tutorials/WhiBal/01/

[PRSearls]

May I suggest adding a white towel in your calibration shots so you can see when detail becomes blocked up (overexposed) or disappears in the shadows. I don't use the zone system but did back in the 70's during my "Ansel Adams 4x5 period."

X-rite's ColorChecker Passport is another useful calibration tool that I use frequently. Its included software will calibrate your camera sensor's color response under any light condition; it's easy and accurate. Here is more info (I have no connection with x-rite but am a happy customer):

http://www.xritephoto.com/custom_pag...FcxAMgodYCEAOg