Introduction: Converting a Foot-Candle Meter for Photography
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For those of you amateur photographers out there who like shooting film, sometimes old cameras don't have the right light meter for getting the correct exposure. Sometimes they are faulty, inaccurate or have no light meter at all! Photographic light meters can be pretty expensive but analog foot-candle meters are cheap because they don't really have any photography purpose, until now. Tthis guide will show you how to put it to work for photography.
Foot-candles are a unit of light that can be directly correlated to Exposure Values (EV) which are a list of simplified amounts of light and are often referenced to possible scenarios which you might find this amount of light in. Paper exposure calculators work on the principle of manually identifying an exposure value based on the description and then aligning the EV scale with your film sensitivity to deduce shutter speed/aperture combinations for your camera.
FC and EV are directly related, so modifying the meter back-panel is all that is required to turn a FC meter into an EV meter, and it works great. It takes all the guesswork out of using a paper exposure calculator which is great for beginners.
Step 1: The Meter
Foot-candle meters read the amount of light striking a surface by having their selenium cell subjected to the same light as the photographic subject is subjected to. In some cases you need to be close to the subject to subject the meter to the same lighting, but in a lot of cases like outside, if the subject is in the sun, and your meter is in the sun, the lighting is the same no matter where you are. You can meter once and keep taking pictures until the subject lighting changes for whatever reason.
The FC meter I used was a General Electric Type 214 foot-candle meter, it has 3 ranges controlled by a switch on the right side, and a plastic-covered selenium cell on top. There is also a small metal grate that can be placed over the cell to drop its sensitivity by 10x so that full daylight can be metered as well.
Step 2: Getting Started
To change the meter backplate we have to make a new one based on the old one's markings. Disassemble the meter and remove the backplate, then put it in a flatbed scanner and scan it into your computer.
Step 3: Making a New Scale
Sekonic is a light meter manufacturer who has kindly put a conversion chart on their website to use in converting the values from foot-candle to EV. Just read the FC value for each EV value and draw lines and numbers on the old meter back-plate to indicate the new EV values.
Use your favorite drawing software to make a new scale, drawing on top of the old one. I recommend using a program that allows layering images so the old scale and new scale pictures don't become mangled together.
If you happen to have found the same light meter as me (GE 214) you can print out the attached PDF and use my template, it is correctly scaled for printing on 8.5x11 paper.
Step 4: Insert and Reassemble
Print out the new scale and tape it over the old one. Reassemble the meter and its done!
Step 5: Using the Meter
To make use of the meter you also need an exposure calculator (http://www.squit.co.uk/photo/exposurecalc.html) which is a wonderful tool made by Andrew Lawn. This tool converts the EV reading to a shutter/aperture combination.
Steps to take a measurement
Place or hold the meter in the same lighting as the subject
Read the EV value off the meter
Slide the Exposure Calculator so the ISO film speed of your film points to the EV value you read
Read the Aperture/Shutter Speed values off the bottom of the Exposure Calculator
Set your camera to these values
See the pictures below for the results!