by Mark Thellmann, InLiquid artist
Kodak makes what is called a gray card, as an aid to perfect exposures, but I have always found this term misleading.
This card just happens to have been printed a neutral gray color, but more importantly it is a surface which reflects exactly 18% of the light which strikes it. Many other colors can do this if they are of like density, not just the color gray. This 18% is a magic percentage, because it is what all light metering devices are calibrated to in order to obtain the perfect exposure for the film you are shooting (providing you remembered to set the ISO number correctly, if your camera requires you to do this manually.)
Most of the time, what you are photographing in nature is reflecting light at this 18% value, but when photographing artwork, unless we are aware of this 18% value, we may get the wrong exposure. For instance, if you are photographing a painting with dark tones, the meter will measure the light reflecting at 18% (that’s all it knows how to do), but the painting is reflecting light at maybe only 9% (its tones are dark and dark means more light is being absorbed than reflected), so the slide is going to come out overexposed one stop (9 is half of 18) and that means the slide will be twice as bright as it should be, leading to loss of detail, tonality, etc. You will be heard throughout the processing lab exclaiming, I’ve lost my detail… my tonality! Exactly the opposite happens with a painting which incorporates a lot of light, airy, soft pastels. This time you will say, I’ve lost my light, airy pastels. This is too dark. It’s blocked up!’
So, how do we acquire the correct exposure? Three possible ways that I know of… 1) Take a TTL (through the lens) meter reading with your camera. If what you are photographing is reflecting light at 18%, your exposure should be right on (providing your camera is working correctly and the lab doesn’t process your film in exhausted chemistry.) If you suspect otherwise, you can bracket your exposures by 1/2 stops: two half stops over and two half stops under or…
Place the gray card in front of your subject and take a meter reading using it by first focusing on the artwork and then carefully removing the camera from the tripod and moving it in so that the gray card completely fills the viewfinder (do not refocus or you will affect bellows factor). Then take your meter reading making sure you, nor the camera, is blocking any of the light or you will be measuring shadow. This should be the proper exposure because you have provided the meter with a source having an 18% reflectance value, which is what the meter is dying to see.
Use a hand held incident light meter and measure your lights directly. Incident meters are not influenced by how much light is being reflected or absorbed by the subject. This is the way they do it in Hollywood.
Take a reflected meter reading and an incident meter reading and average the two together. Use this exposure. If you have taken copious notes, you be able to determine which method works best for you and finally exclaim, I am a great art photographer! Just look at this!
Mark D. Thellmann has been an art photographer, fine artist, and photography instructor for the past 25 years. He has recently produced a video entitled Take Perfect Photos of Your Art and Craftwork which discusses and demonstrates the necessary camera equipment, lighting, film exposure and methods of photographing paintings, sculpture, woodworking projects, fabric art and jewelry.
A second video entitled Alternative Photographic Processes with Polaroid Films (time-Zero film manipulation, image transfer and emulsion transfer) reveals the techniques Mark uses to create fine art. These fine art images can be found in the Polaroid Museum Collection and on greeting cards and posters throughout Europe, the U.S. and Canada.
All materials copyright Mark Thellmann. No reproduction without permission. ALL RIGHTS RESERVED.
Images copyright © Part V: Obtaining the Proper Photographic Exposure
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