Rafael Echeverria , Nov 28, 1999; 04:08 p.m.
Does a grey card help out if you're photgraphing people?
Bill Schaffel , Nov 28, 1999; 05:58 p.m.
All photo meters are designed to average the subject they see to 18% middle gray, which is the same as a gray card. Without a detailed explanation of the Zone system, 18% middle gray is zone 5. light skinned people are in zone 6 while dark skinned people are usually in zone 4 and there are skin tones and lighting circumstances that put some people in zone 5. If you meter off a gray card, everything else should wind up properly exposed.If you meter the subject's skin, then you would have to use exposure compensation to get the correct skin tone.
Scott Eaton , Nov 28, 1999; 07:41 p.m.
Grey cards help with metering ANY situation, not just people.
Rafael Echeverria , Nov 28, 1999; 07:50 p.m.
Here's another question to add to the above: What if I am indoors and I need to use a flash. Now if I take a reading off the grey card and it tell me x exposure y time, now when I use my flash, how will that affect the photo? Won't the flash make the photo over exposed? Thank you all in advance for your help and patience.
Rafael Echeverria , Nov 28, 1999; 07:53 p.m.
Sorry, I meant x aperture.
Marc Sitkin , Nov 28, 1999; 08:04 p.m.
You can get the same benefit by taking an incident meter reading.
Jim Strutz , Nov 28, 1999; 11:20 p.m.
As to your second question...
If you determine correct ambient exposure by way of a grey card or any other means and then add a full dose of flash; yes, it will be overexposed. However, the highlights will be affected less than the shadows so the result will mostly be a reduction in contrast.
This happens because there are areas in most scenes that are, perhaps, 2 stops brighter than average and other areas that are 2 stops darker than the average. The shadowed areas will be brought up to the average brightness with the flash, but a 2 stop highlight area will only have 1/4 more light added to it. This will not be nearly as appearant.
Still, the usual procedure for adding flash to an otherwise properly exposed picture is to reduce the amount of fill flash by 1-3 stops. That way it is not so noticeable and still reduces the darkness of the shadows.
Ellis Vener 
, Nov 29, 1999; 01:36 a.m.
Bill, not to get too technical but your assumption that " All photo meters are designed to average the subject they see to 18% middle gray" is wrong, different meters have different biases both as to what is "middle gray" and also to different colors and parts of the spectrum.
Rafael, one thing to consider is the angle at which you set the gray card respective to the light. There are no shortcuts to learning good exposue techniques. Learning those techniques (and using a gray card or even learning the zone system for that matter are only teaching tools -- not absolutes to be rigidly adhered to) and then applying what you learn along the way until the process becomes intuitive is the only way. This isn't a hypothetical "technology vs. art" issue; it's a very real and powerful paradigm.
Since you don't state what your problem is it is impossible to offer a more definitive answer, at least from where I sit.
As to your second question: yes either you or your camera need to know what the total illumination will be to accurately make a judgement as to what the best exposure will be. Adding flash obviously changes the equation of an exposure calculated purely by existing ambient light.
Tom Johnston , Nov 29, 1999; 03:44 p.m.
At the risk of causing a war again, I will once again point out that reflected light meters ARE NOT calibrated to 18% reflectance. The last time I mentioned this I was attacked as if I had said "God is dead" at a revivalist meeting. Knowledgeable photographers know better and I never cease to be amazed that "armchair" experts still cling to this myth.
Bob Atkins 
, Nov 29, 1999; 05:58 p.m.
Tom - Please tell us what they are calibrated to, and
cite a literature reference if you have one.
I don't think we need to repeat
this thread again, but some info would be nice.
Unless ALL meters are supposed to be calibrated to some defined standard, we
would have to run calibration checks with every time we used a new
meter. Some do that I suppose, but normally when meters disagree it's
put down to miscalibration, not calibration to a different standard. So
what's it supposed to be? 8%, 12%, 18% or is there in fact no standard
at all?
I know these points are covered in the other thread cited, so maybe people should
just go there and read what's already been written!
It would be nice if you could cite an authoritative manufacturer's web site
statement about exactly how their meters are calibrated. Is there an ISO/ANSI
standard which relates to the calibration of exposure meters I wonder?
I did find the follwing via a web search, but I only have the document title,
nothing about its contents:
Document Number: ISO 2720:1974
Title: Photography - General purpose photographic exposure meters (photoelectric type) - Guide to
product specification
Alan Gibson , Nov 29, 1999; 08:09 p.m.
[Let sleeping threads lie?]
I haven't read 2720 (my library no longer stocks standards), but I understand it doesn't calibrate meters with respect to percentage reflectances, but wrt luminance values. I also understand it allows a range of calibrations (which is reasonable, as no meter could be manufactured with a zero tolerance), but the tolerance is a rather generous third of a stop (i.e. plus or minus a sixth).
As always, if someone who has actually read the standard, I would welcome any comment/corrections.
Terry Carraway , Nov 30, 1999; 09:52 a.m.
As I understand it, the ANSI standard for meters cites a 12.5% reflectance.
The problem is these standards are copyrighted and closely held, except if you part with money first.
Ellis Vener , Nov 30, 1999; 11:18 a.m.
Exposure:If you are going to use a gray card to help determine your exposure, even after you test and find how you need to calibrate your meter and exposure settings to produce a perfect match print or transparency reproduction of the gray card photographed under ideal circumstances, you'll still need to be ultra careful to make sure that when you use a grey card in a 'real world' photograph that the angle at which you set it in relation to your lighting and camera doesn't include a glare factor in the intensity of light reflected by the gray card.
Color Balance: This is a trickier question. Every color film manufacturer has their own bias as to what they think is the best flesh tone. Taken a step further down to the path of critical rendition of color, each individual film inside each of those broad families has its own palette of color as well. This makes the choice of film a subjective one. And if your end result is prints, there is also the matter of how the paper renders the colors recorded by the film. A gray card or a Macbeth color grid will help you get in the general vicinity but you'll have to decide which rendition matches your vision. Unless you are testing -- and I think this is a worthwhile series of tests to undertake -- to see how lots of different people's skin tones relate to an absolute standard photographed in the same standardized light with the same standardized film & processing. This test will be useful to help sensitize your eye and will also help you be able to talk with your lab.
Robert Bumb , Dec 04, 1999; 01:18 p.m.
ANSI PH3.49-1971 Advisory and not mandatory. Reflected light meter calibration to 12% reflectance, allowable error plus or minus 2%.
Robert Bumb , Dec 05, 1999; 02:51 p.m.
At the Sekonic users forum, http://mamiya.com/cgi-bin/WebX?13@^4068@.ee6b791 , under the title Calibration Constants, Danny Cirillo of Mamiya America lists the reflectivity constant for Sekonic meters as 12.5 and Minolta as 14. The Sekonic owner's manual list 12.5.
Alan Gibson , Dec 06, 1999; 08:22 a.m.
It's a shame Danny doesn't quote the units, so we don't know if this is a percentage reflection or really (as I suspect) something else. Lack of units causes problems in photography, as well as Mars spacecraft.
Christian Becker , Dec 06, 1999; 11:17 a.m.
Yep. They'll have something to hold or watch while waiting for you (fumbling with your camera)to prepare for the shot.
On the streets it makes up for nice scenes
OHHH BABY, WOULD YOU LIKE TO SEE MY ------ grey card ????
Robert Bumb , Dec 09, 1999; 07:22 p.m.
Alan,in addition to ANSI PH3.49-1971 which sites percentage reflectance see; Ctein, pg. 29,Post Exposure, Advanced Techniques for the Photographic Printer, Focal Press, Boston, Oxford and others,1997.and Silverman, Zuckerman and Shell, pg. 74, The Hand Held Exposure Meter Book,Photo Books Division, Mamiya Corporation of America, 1999 for reflectance percentage values. Ctein gives an interesting discussion on the problems created by the standard.
