Exposure and Light meters

DeJur Dual Pro circa 1952

Recently I posed a question on social media.  I must admit I intentionally attempted to mislead people.  My question was, “Do you use a light meter when you take photographs?”  Most of those that replied answered no.  The fact is, virtually every one of them uses a light meter, they just didn’t realize it.  Why most are shooting in some sort of “auto” mode.  I will even count Program (P), Shutter priority  (S or Tv), and Aperture priority (A or Av) as quasi-auto modes.  In using those modes you set (or can adjust) a value and the camera determines a corresponding value (i.e. I set the shutter speed the camera will set the aperture).

This automation has allowed us to get somewhat lazy and we forget or never knew our camera was using its built-in light meter to make a portion of the settings to achieve a balanced exposure.

Let me digress for a moment and let us first discuss the components of photographic exposure.  We will start with the exposure triangle.

Three settings control exposure.  ISO (film speed or sensor sensitivity), shutter speed, and aperture.  If you change one setting you will have to adjust another to maintain a balanced exposure.  Think of a balance scale, we want both sides of the scale to be equal and the indicator to be on the zero mark.

For the sake of this discussion, we will leave are ISO constant and will only discuss changing shutter speed and/or aperture.

In shutter priority mode, the photographer sets the shutter speed.  When we press the shutter release button the camera will do many things which will include, activate the built-in light meter and take a reading.  Based on that reading the camera will determine how to set the aperture and then select that aperture for the photographer.  In aperture priority, it is just the opposite, with the camera selecting the shutter speed based on the aperture set by the photographer.

While this is a great system it also has some drawbacks which can lead to blurry or under/over exposed photographs if the camera can’t make enough of an adjustment based on its or the lens’ limitations.  If the photographer doesn’t know how to read the built-in meter display.

So what does this meter display look like?

As seen looking through the viewfinder

In fact, when we look through the viewfinder your camera will display a lot of information, but for this article, we will discuss the meter reading which is the scale between the 2.0 and ISO 100.  Below is a more isolated view.

When we have a balanced exposure the indicator will be in the center which can be a zero (0) or an arrow.  Over/Under exposure is indicated when the highlighted bar moves towards the plus sign (+) for overexposure or the minus (-) for underexposure.

Back in the days of old, when I started in photography we had to learn to read the meter because our cameras of the time were manual, not “auto” or scene modes.  We set everything, including focus.  The photo below is what the meter in my first camera looks like, yes I still have it and it still works.

Let us examine the meter above.  We set the ISO (often referred to as ASA at the time) based on what film we loaded.  We then set the lens to the aperture we wanted to use and the meter gave us the shutter speed.  Some meters were merely an indicator with a “zero” line and the goal was to get the camera set to nearly zero (unless you were wanting to specifically over or under expose.

Learn to read the meter and you will learn to see light and have much more creative control over your exposures.

Next time I will talk about metering modes.



1 thought on “Exposure and Light meters”

Leave a Reply