The outcome of the photos that we take are the result of the setting of the camera and pressing the shutter button. Here are some tips on using a light meter to help you take better photos.
These settings are the shutter speed and the f-stop settings given by the amount of light in the composition. This can be measured with a light meter. Light meters where built to get the correct exposure, by measuring the light. Also, there are two different types of light: incident (amount of light falling on the subject) and reflective light (amount of light reflected from the subject). You must know, a built-in camera light meter measures only reflective light.
Whether you use color negative, black and white or slide film, the camera must be set to a shutter speed and f-stop matching the conditions (for slide film), or to an aproximate value (color negative and black and white film).
For negative film, it’s not necessary to own a light meter, the exposure can be measured with the Sunny 16 rule (On a sunny day and with ISO 100 film / setting in the camera, one sets the aperture to f/16 and the shutter speed to 1/100 or 1/125 second) due to the films tolerance.
For slides, for getting the right exposure, is best to use a handheld light meter, a built-in light meter, a digital camera or your iphone (there’s an app for that). To measure with the light meter you must know what ISO your film is and what your camera’s capabilities are (aperture, shutter speed). If you have only one f-stop (say f8) you have to either set to “Aperture Priority” (some meters have this option) or read times for “f8”. Same thing for only one shutter speed, but most cameras have a bulb mode, so I suggest using that, if not push or pull your film, depending on your needs.
Set the ISO speed of your film, set any one of those priorities (aperture or shutter speed) and open the meters window. The result is a correct exposure for the amount of light in your composition. Now, the standard for the film speed has change a bit. Until 3 decades ago there where used about 3 sandards, DIN, GOST and ASA (or today’s ISO). If you use an old russian light meter, who uses GOST film speed, or any other, there’s a chart made by Wikipedia who can be very useful.
The last method for measure, is by using your iPhone. There are a couple of apps like PocketLightMeter, LightMeter or others, that work the same manner as traditional meters. Also remember, there’s a setting on what type of light you are measuring, incident or reflective light. These apps are using the front and back camera of the iPhone and it may not work in conditions of 2-3 EV (very dim light). I think FotometerPro is the best, has a nice interface and it’s giving results close with a standard electronic lightmeter.