Jim Church's Cows
Part IV

by Roger Roth


Ladies, let me explain exposure meters in words you will all instinctively understand:

All exposure meters are male:

  • They won't stop and ask for directions.
  • They have only one thing on their minds.
  • If they don't get what they want, they cheat.


Let's KISS (keep it super simple).  Let's think in terms of black & white photography--you aim your exposure meter at the subject, and the meter gives you an exposure reading (often the f-stop for a given shutter speed).

  • An exposure meter only measures what it sees, and it only sees what you aim it at.  It doesn't stop and ask you for aiming directions.
  • An exposure meter only has one thing on it's mind--it lusts for an average shade of gray (called 18% gray). An exposure meter only has one thing on its mind: it wants the entire world to be gray.
  • If an exposure meter sees another shade--such as black or white—it will cheat and turn that shade to gray.

Ladies, you can stop here if you wish--you have the idea.


It was a warm, sunny day, and the farmer decided to photograph some of his cows. He set his camera's built-in metering for "spot metering."  (The spot meter setting tells his exposure meter to only look at a small area in the middle of the picture.)

His first model was Elsie, only white cow in the herd. His trusty spot metering system saw only Elsie's bright, white body and zappo--the farmer had his first picture.

Elmer, the black bull was his second next subject.  The spot meter saw his black body, and zappo again--the farmer had his second picture.

Dlberta, the gray cow, was his last subject -- yeah, another zappo and another picture.

When the pictures were processed, the farmer stared in utter disbelief.  He'd spent a zillion bucks to buy a farmer-proof, fully-automatic camera, and his pictures all looked the same.  All three of the cows were gray.  Why?  It's because the exposure meter lusted for gray and cheated.  (Hey, meters are male.)


The moral of the story is: If you want your white cows to be white, your black cows to be black, and your gray cows to be gray, aim your exposure meter at a gray cow.


  • Try aiming at the mid-water background rather than someone's black wetsuit and BC, or a dark shadow area of the reef or wall.
  • With upward silhouettes aim not directly at it.
  • With a spot meter, try aiming off the palm of your hand (held so the sun strikes it directly--not shaded by your head) and then open one f-stop (lower f-number) to keep your hand from going gray.


You can use this test with any in-camera or hand-held exposure meter.

  1. Set the ISO and film speed for 60.
  2. Stand so the unobscured sun is behind you.
  3. Aim the camera or meter at green grass.
  4. Depress the shutter speed release partway and look in the viewfinder.
  5. Nikonos V - "60" should appear in the viewfinder.
  6. Housed camera: analog scale should center on zero.
  7. Hand-held meter should read f16 and ISO 64 and 1/60 second.

You can also use the palm of your hand as a test target.  Hold your palm a few inches from the lens or meter. Tilt your palm so it faces the sun so direct sunlight strikes your unshaded palm--you don't need to focus.  The metered f-stop should read f22 (not f16).

You can adjust the ISO setting so the meter reads f16 for grass or f22 for your palm.  This "adjusted" ISO setting is your "EI" (exposure index) and can be used in place of the ISO speed of the film.


  1. Find a scenic view with a vary of shades and colors--one that exposes properly at f16 and the ISO closest to your shutter speed is ideal.
  2. With camera on a tripod, shoot 36 shots on E-6 color slide film.
  3. Each time you have film processed at a resort, or dive boat, have the processor snip off a few inches of this test roll and include it in the processing.
  4. After each daily processing run, you have a standard scene for comparing variations in processing from day to day.

Critter corner: The cowfish’s diet may usually consist of sponges, tunicates, and shrimp.  Many times they will be found blowing jets of water into the substrate to “scare up” their food.

copyright © Roger Roth, 2002 - 2011

Photo Competition

Roger Roth is a roofer by trade and lives in Cincinnati, Ohio. But his passion is underwater videography and after several decades of learning how to shoot and edit he has evolved into a teacher and a photographic philanthropist. Roger is the founder of the annual international Underwater Images Photo and Video Competition. You may contact Roger at