Moose Peterson has an excellent tutorial on the use of flash on his website, and there’s little that one can add to that. So, for overall information on TTL flash work, check out excellent essay.
But there is one thing that’s not covered there, and does not seem to be generally covered in books and articles about TTL flash. And that is the impact of film reflectivity on TTL systems that use "off the film" (OTF) metering…
Well, the idea is simple…
TTL (through the lens) metered flash works by cutting off the flash when the correct exposure level is achieved. Basically, the camera fires the flash and a sensor monitors how much light is put out. Once the correct amount of light has been reached, the camera shuts off the flash.
In many cameras, the sensor that monitors the amount of light put out by the flash are actually measuring the light reflected back off the film – hence the phrase, "off the film" metering. Obviously, when you reflect light off something, the degree of reflectivity makes a difference.
The image below shows a potpourri of different brands and types of films. I just raided my freezer and film bag and pulled out one of everything there… As you can see – the different film types are pretty different in color and overall darkness or lightness. In fact, when I ran a spot meter over the different types, there was over 1.5 stops worth of difference in the meter readings from the lightest to the darkest film emulsion.
Many brands of film...
Does this have an effect on the exposures gotten via TTL flash? Absolutely! I learned about this while trying to diagnose exposure problems with a roll of Kodachrome it took last summer. I was out taking insect macros and on this particular day had shot two rolls of print film, one roll of Kodachrome, and one role of Kodak Elitechrome EBX. All of the images were properly exposed, except for the roll of Kodachrome – which was consistently under exposed. Since the roll of Kodachrome was shot in the middle of the sequence, I could not figure out what change in technique or equipment settings could account for the exposure problem.
Then the question about TTL flash came to mind. When I compared the Kodachrome to the other film types, the hypothesis was confirmed. Kodachrome is a very light colored (more reflective) film. So… more light bounces off it, the TTL meter cuts out the flash that much sooner, and as a result the images were slightly under exposed.
Of course – for print film a stop or even a stop and a half of mis-exposure will not be catastrophic. But for fairly narrow latitude slide films, such exposure problems would certainly be noticeable.
I responded to this problem by just not using Kodachrome for this kind of work… I just use the film brands that I know will work with my system.
But, if I wanted to keep using Kodachrome, or found problems with other films, the answer would be to calibrate the TTL meter with a gray card, basically shooting some sample shots to confirm that the exposure is correct, and then adjust setting accordingly. I suspect that to use Kodachrome for with my technique of shooting insects, I’d need to dial in ½ to 1 stop of positive flash compensation.
Photos accompany article appearing in Michigan Birds & Natural History, (April-June 1999) v 6, no. 2:
Normal Coloration:
Normal Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Chicadee:
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Leucistic Black Capped Chickadee In Kalamazoo County, Michigan
Mark Cassino is a fine art and natural history photographer based out of Kalamazoo, Michigan. His work runs the gamut from micro-photographs of individual snow crystals, to close ups of butterflies and birds, to landscapes depicting Michigan’s unique terrain.
Mark uses a variety of techniques to create his unique images. He works with the latest digital technology, but also utilizes medium format film cameras and toy, junk, and antique devices. His creative techniques include extreme close up photography, digital and film based infrared photography, alternative B&W processing techniques, and digital enhancement.
Working from both a scientific and artistic perspective, Mark’s works have been exhibited in a diverse variety of venues.
His scientific photos have been displayed in the gallery of the National Botanical Gardens in Washington, D.C., on several covers of American Entomologist, in Science World, and in numerous textbooks, calendars, and trade publications. His work has appeared on many science oriented websites, including those of the US Department of Agriculture’s Systemic Entomology Laboratory, NASA, and the popular radio series Earth and Sky.
His fine art work has appeared in national and regional juried art shows, including the 2003, 2004, 2005, 2009 and 2011 West Michigan Area Show, sponsored by the Kalamazoo Institute of Art and the 2004, 2006, 2008 and 2014 American Landscapes national juried show sponsored by the Maryland Federation of Art. His work has also appeared in The “Rural Outdoors” and "Selected Works from the Rural Outdoors" exhibits in New York State, the 2005 All Michigan / All Media exhibit, sponsored by Ferris State University’s Rankin Art Gallery and the 2006 Krappy Kamera Contest, a national exhibit of photos taken with toy cameras, hosted by the Soho Photo Gallery in New York City. Two of his photos were accepted into the 2008 Macroworld competition, hosted by the Center for Fine Art Photography in Fort Collins, Colorado. One of his pieces was also accepted into the 2008 Street Photography competition, also hosted by the Center For Fine Art Photography.
One of Mark’s specialties is close up photos of individual snow crystals. His technique utilizes ordinary photographic equipment to capture close up images of the tiny crystals. Mark teamed with physicist Jon Nelson to write The Story of Snow: The Science of Winter’s Wonder which was published in October, 2009, by Chronicle books. The book was named an Outstanding Science Trade Book by National Science Teachers Association, received a Blue Ribbon award from the Bulletin of the Center for Children’s Books, was a Junior Library Guild Selection and was included in the Chicago Public Library’s Best of the Best” list for 2010. The Story of Snow has been published in Japanese, Korean and Chinese editions. Six years after its original publication The Story of Snow continues to be a popular with kids, parents and educators.
Updated: 3/26/2015