Just about anyone who has ever tried to photograph a full moon against the night sky with their camera on automatic knows how disappointing this can be.

In trying to re-create this for my students, I draped a black backdrop on the wall. Then I enlisted Jose to be “Zorro. ” I draped a smaller black sheet around  him so that only his face was visible.

With 2 photo flood lights positioned on either side of Zorro, I used my 50 mm lens set the exposure as recommended by the camera. ISO 400 f2 @1/20sec

I intentionally framed my picture loose so that Zorro‘s head is small– sort of like the full moon you would see against the night sky. Note also the metering mode was set to Partial.

As expected Zorro’s face was devoid of detail, highlights were blown out.

A quick way to correct for this camera meter flaw is to move in closer and fill the frame with your subject.

Just as in my slightly out-of-focus picture on the left shows, metering for exposure works independent of focusing.

I just wanted to make an exposure so I could have a jpeg file to read the metadata for the closeup meter reading.

Then I stepped back and used the new settings I got: ISO 400 1/125 sec @ f2.8.

I tried to stand at about the same approximate place I took the first picture. Notice the improvement?

In the film days, most camera manuals would explain why this is so. It was basic and part of learning how to get reliable exposures.
I guess with instant feedback readily available via the LCD monitor, owner’s manuals don’t mention this anymore.

It’s only through doing this exercise that I think some folks can reconcile what I mean when you hear that exposure meters inside cameras can be fooled.

Meters are made to try and render every scene  18 % grey.

So when “Zorro’s” face takes up such a small percentage of the total viewfinder, the meter is thinking, “Dang, this is very dark. My job is to make that black closer to grey, so I must allow in more light to change black to grey.”

Those of you who have a little more experience can probably see how the opposite situation can fool your camera’s meter.

That’s the case when you’re up in the snow or at the beach.

 Only this time, the camera is squinting as it were. It’s thinking, “Yikes, it’s way too bright out here, I better not let so much light in.  I want to be sure all the snow is not so white, just grey.”

In this instance, you can guess that you’ll need to let in more light either dropping your shutter speed to something slower or opening up the aperture. Either one will work to prevent underexposure.