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grey card

Rafael Echeverria , Nov 28, 1999; 04:08 p.m.

Does a grey card help out if you're photgraphing people?

Responses


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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


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