Test Your Meter
35mm SLR, Tamron 70-210mm f-2.8, Fuji Provia 100, 1/125 sec at f-11, Bogen tripod and Ball head. Aperture Priority, Centerweighted metering.
Exposure seems to be the most difficult part of photography
for many. There are those who totally rely on their camera meters and those who want to
use their meters as a starting point. Relying on your camera all the time can give good
exposure some of the times but not all the time. I look at all the built-in features in my
camera as tools that are designed for me to control, rather than them controlling me.
All
meters are designed to produce middletone results. Middletone is neither black nor white,
its neither light nor dark. It is half way in between. Green grass, blue sky, tree trunks
for example are all middletone. Your camera meter should give proper exposure when
photographing a middletone subject, otherwise you must compensate. This is true regardless
of the type of camera or built-in meter you have.
This is an 18% gray color or middletone
First thing you should do with any
meter, whether camera or hand meters is to make sure it is calibrated correctly. Meters
can be off by several stops resulting in wrong exposures. You don't have to send your
camera for repair if your meter is off. You can easily calibrate it yourself by using the
Sunny f-16 rule.
The Sunny f-16 Rule
Sunny f-16 rule states that correct exposure for a frontlit middletone
subject in bright sun, two hours after sunrise and two hours before sunset, is f-16 at the
shutter speed closest to the film's ISO. With an ISO 50 film for example, your exposure
would be 1/60 at f-16, or 1/125 sec at f-16 with ISO 100. You can use any equivalent
exposure when using the Sunny f-16 rule. With ISO 50 film you can use 1/125 sec at f-11,
1/250 sec at f-8 and so on. All these combinations provide same overall exposure. Use
Sunny f-16 in bright sun to photograph middletone subject regardless of what your meter
says. You will get the best exposure by using the Sunny f-16 rule. Knowing this, you can
test your meter and calibrate it if necessary. Go out on a clear sunny day. Set your
camera on manual exposure mode. Set your ISO dial to the type of film you use most. It can
be any ISO and you don't have to load any film. Set your f-stop to f-16. Now focus on a
middletone subject that is frontlit and make sure it fills most of the viewfinder.
Right Image: This image is a perfect
example of Sunny f-16 rule. Everything in this image is of medium tone.
Pentax 67, 75mm lens (equivalent to about 35mm lens in 35mm format), 1/60
sec at f-16, Fuji Velvia ISO 50, Bogen tripod and ballhead.
An 18%
gray card which can be purchased at any photo supplier ( see below) is great for this test. You can
also use the sky, green grass, or even your faded blue jeans. Change shutter speed and set
it to the number closest to the ISO you set. For instance, if you set ISO dial to 100,
your meter should read zero when shutter speed is set to 1/125 at f-16. If you get this
reading, your meter is fine, otherwise you must calibrate it. If the meter does not zero,
change ISO until it does. It doesn't matter which number you end up with. You may end up
with ISO 200 or ISO 50 or any other number. Note this number and use it whenever you use
the ISO you tested it for. If setting ISO to 200 gave zero reading with ISO 100, then you
would set your ISO to 200 whenever using ISO 100 film. You should run this test with all
film speeds you use. This has nothing to do with pushing or pulling films or film
processing times. You simply corrected your meter.
You can do this test if you have a
separate hand meter. With incident light meters, hold the meter so the dome is pointed at
the light. Set it to the shutter speed closest to the ISO you want to calibrate your meter
to and take a reading. Meters have dials for calibration. If the meter does not give f-16,
turn the dial to re-calibrate.