Achieving correct exposure

I have four friends who own professional photography labs. They are all unanimous in stating the single greatest problem experienced in their labs is poor exposure. And of course, they are expected to fix this basic photographer’s error.

So I wanted to take a moment to review exposure and what to look for in good exposure.

As we understand, good exposure holds detail in the darker or shadow end of the scale and in the lightest or highlight end of the scale as well. What this achieves is a well-balanced image without plugged shadows and blown-out highlights.

We must remember two things. First, exposure is dependent upon light intensity, the reflectance of the subject and to a certain degree, the color of the subject. And secondly, exposure measurement systems, whether hand held meters or those in the camera, attempt to make the average of any scene mid-tone.

So, the perfect solution is to measure a mid-tone photographic gray card in the light of our scene. Theory is that if mid-tone gray is accurate, all other tones will fall into their appropriate place on our histogram. Perfect! But in practical applications, we cannot always add a gray card in our scene and fiddle with exposure. Our flea will have flown and be long gone by that time!

So now what? First let’s be sure our camera is exposing properly. I am surprised that of my students, most of their cameras (75%)  do not expose accurately.

To find out where your camera exposes, shoot a photographic standard gray card in even light. Fill the frame with the card. Review the histogram. It should have a single spike directly in the middle of the tone range. If not, the camera over- or under-exposes by a certain degree. Adjust the exposure compensation until the spike is centered. This is your default error. Use that compensation in your subsequent photography and you will be more accurate.

The image below is a well-exposed gray card and its histogram. You can see the single spike in the center of the tone range. This is ideal.

Let’s look at a more difficult pair of images.

In the top image below, a common facial tissue is photographed with diffused lighting using my camera’s exposure error default. (Plus 2/3 F stop.) And knowing the tissue is lighter than mid tone in reflectance, I also opened up another 2/3 stop. This was done to place the values of the tissue correctly in the highlight side of the histogram. (Not a mid-tone gray tissue.)

Then I added the stink bug, a dark gray insect with lots of detail. With the previous corrections, this insect and the tissue on the background photographed with appropriate tone values for all components of the image.

Nikon D2Xs, Micro Nikkor 200 mm F 4.0 macro lens. SB-800 with diffuser panel.

Now the key is to standardize your own system. Know where your camera exposes. Make appropriate corrections to this built-in error. Use the default corrections when you shoot and be aware of the reflectance of the subject, making appropriate adjustments where required. All cameras and metering systems are different. And remember that metering modes, like 3D-Matrix or Evaluative, meter differently than spot or center weighted.

© Brian Loflin 2011. All rights reserved.


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