Is Your Light Meter "Puttin' the Shuck on You?"

Howdy gang.  Shutter Brother Kelley here with another dive into the cookie jar of film photography topics.  Let’s face it.  If we are engaged in some form of serious photography, then I’m sure that most of us, if not all have at one time or another used a light meter to arrive at the correct exposure setting before pressing the shutter.  There is even a good chance that some in our hobby would not even consider using a camera that did not have an on-board light meter.  No doubt these light meters have come a long way since they first began showing up on cameras many years ago.  And certainly, with the re-introduction of Kodak Ektachrome slide film, I am sure that we all will be relying on our light meters more.

 

Is your light meter "giving you the business?"

Our Uncle Jonesy (for whom this blog, and our podcast is named) had a phrase he used when someone was giving him less than reliable info on a particular subject, or even going as far as intentionally misleading someone. If Kevin or I said to him that someone told us this or that, he would reply, “Well, that person was puttin’ the shuck on you.” On the old television series Leave It to Beaver, Wally would warn his little brother that someone, usually Eddie Haskel, was “giving him the business.”  So now we ask the question, is your camera's light meter giving you an accurate reading?  Or, as Uncle Jonesy would say, “Is that thing puttin’ the shuck on you?”  How do we really know if our light meters are the accurate measuring devices we trust them to be, or are they just giving you the business.  This is a truly legitimate question in light of the fact that most of us shooting film are using cameras that are at least 15 years old.  Some, like my trusty Nikon F3HP are much older.  The truth is, you can line up three or more vintage 35mm SLR’s, meter a scene with the same exposure settings, and you will get three different results from each camera’s meter.  What do we do now?

First, let’s remind ourselves just what a light meter is supposed to do.  A light meter measures the average amount of light in the scene you have chosen to photograph, and gives you the correct exposure setting based on a known standard.  We refer to that standard as 18% gray.  When you frame your subject, your meter takes the bright areas of the frame, and the dark areas of the frame, along with everything in between, and creates an average light value which is our known standard of 18% gray.  This value is then compared to the exposure settings you have selected on your camera, and lets you know if you have the adjust those settings.  If you are using an automatic exposure mode on your camera, the meter selects the correct settings for you.  If the light meter on your camera is accurate, you are good to go.  If it is not accurate, well, you know what Uncle Jonesy would say.

 

My 18% gray card.  What your meter wants to see

But don’t worry.  Here is a quick and easy way to determine the accuracy of your light meter, and, if it is not accurate, calibrate it so you can restore trust.  We can do this because we photographers also have a “known standard” for exposure, and it is called “Sunny 16.”  More than likely, you have heard Kevin and I discuss Sunny 16 on our podcast, or perhaps you have read or heard about it from another source.  It goes like this.  On a bright and sunny day with no clouds with the sun behind your back, you simply set your shutter dial to match the ISO rating of your film, and set your aperture to f16.  For example, if you are shooting Kodak Ektar (100 IS0), set your shutter to 1/125, and the aperture to f16.  This will be the correct exposure setting on a bright sunny day with the sun behind you.  Your camera’s meter, if it is accurate, should confirm this.  So let’s test your camera’s meter to see if it is giving you accurate information.  To do this, first you need a bright sunny day with no clouds.  You will also need an 18% gray card.  They are available from most photographic outlets.  I purchased mine on Ebay.  Remember that your meter averages the light it sees and gives you the exposure settings to make your subject 18% gray.  Using your normal lens (50mm), choose an ISO setting (I always use 100), and manually set your camera exposure settings accordingly (shutter set to 1/125 sec, aperture set to f16).  Now look through the viewfinder and aim your camera at the 18% gray card which you have placed in the direct sunlight and check your meter.  It should be telling you that you have selected the correct exposure settings.  If not, adjust the ISO setting on your camera until the meter tells you your exposure is correct.  Remember: we already know the correct exposure settings for a brightly lighted scene with the sun behind you.  Your camera’s meter should give you the same results.  If it isn’t, adjust your ISO setting until it does.  Now your meter is calibrated to our known exposure standard of Sunny 16.  Hopefully your meter required no adjustment, which means it is 100% accurate.  This, however, is rarely the case, especially with older cameras.  I have tested each of my 35mm SLR’s on the same day with a bright sunny sky.  Each of these cameras required a different degree of adjustment.  In order to remember how much I have to alter the ISO setting, I have placed a small label on each camera that tells me how many stops I have to add or subtract from the film’s ISO setting.  My Minolta X-570, for example requires me to add one stop to the ISO, meaning that I now shoot Tri X 400 at ISO 200.  My Pentax Spotmatic, however, requires me to subtract 2/3 of a stop.  Regardless of the amount of adjustment needed, I know that my cameras are now calibrated to Sunny 16.  Neat!

Now I can handle the truth

I do make the claim that this is a scientific way of calibrating your camera’s light meter, not does it take the place of having your camera serviced by a qualified technician.  It does, however, provide a reliable way to evaluate the information your light meter provides.  And, if you are like me in that I shoot with several different cameras, this method does allow me to bring each camera into the same consistent standard (Sunny 16) that I use in my photography anytime I am shooting without a meter.  So next time you get one of those bright, cloudless, sunny days, take your camera outside with your 18% gray card and see if your light meter is telling you the truth, or, as Uncle Jonesy would say, "puttin’ the shuck on you."