Matthew Kees is a very talented photographer and teacher. He is doing a 5 part series on the MCP Actions Blog on Using a Modern Flash for Portraits. I am excited to share his knowledge and expertise with all of my readers. These tutorials will launch once every other week. On the alternate weeks, time permitting, Matthew will look through the COMMENT section and answer some of your questions. So make sure to ask your questions directly in the comment section about this post.
This is Part 1 of 5.
by Matthew L Kees, guest to the MCP Actions Blog
Director of MLKstudios.com Online Photography Course [MOPC]
TTL OTF Flash (“if the shoe fits…”)
One of the greatest advancements to flash photography came in 1974 when Olympus announced their OM-2 camera and the Quick Auto 310 TTL OTF flash. The two worked together in “dedicated” flash mode.
What this means, is the camera and flash have the ability to communicate with one another. The flash output is controlled by an “eye” or sensor, located inside the camera body which reads the light that has passed Through The Lens (TTL) and bounced Off The Film (OTF).
TTL OTF metering was made possible through additional “dots” on the camera’s hot shoe that matched up with additional contacts on the foot of the flash. The flash and camera were able to “talk” to each other through those extra connections. The sensor inside the camera told the flash when enough light had reached the film during the exposure, and cut the flash off so no more light was produced. The result was a perfect flash exposure every time.
Before we can move forward, I first need to explain some older flash technology.
The way the output of a flash light is controlled in Manual mode, is that at a high power setting the burst of the flash, or the flash pulse, lasts longer than it does at a low power setting. At the maximum setting the flash pulse has a duration of around 1/1000 of a second long — a big “poof” of light. At the lowest power setting it is closer to 1/40,000 of a second — a little “twink” of light.
When a modern flash is mounted on a film camera and set to TTL OTF mode, the OTF sensor bases the flash pulse duration on the camera’s meter setting. Typically, the ISO is set to the rating on the box that the film came in. This is because low ISO films require more light to make a good exposure than high ISO films.
If you want less flash than the film actually needs, such as a touch of fill light outdoors, you simply change the ISO setting on the camera body, to one higher than the film’s box rating. The true rating of the film doesn’t actually change so in essence, you are fooling the OTF sensor into thinking the film that was loaded needs less flash light than it really does. For more flash light you would lower the ISO setting.
Digital cameras are different. You can’t fool the sensor by changing the ISO setting. Adjusting the ISO setting on a digital SLR it is like instantly changing the film to one with a new box rating. The sensitivity of the chip increases with a higher ISO setting or decreases with a lower ISO, so a new TTL flash adjustment needed to be invented.
Modern flashes, and most DSLR camera bodies, have added an EV setting for the flash when set to TTL mode.
EV stands for Exposure Value. When you set the ISO, f/stop and shutter speed using an exposure meter, it is based on the Exposure Value for that scene. You can then adjust the brightness of the scene by changing the EV setting on the camera body. An EV plus makes the scene brighter and an EV minus makes it darker. To adjust the flash brightness, you must change the EV setting of the flash. This is often referred to as Flash Exposure Compensation or FEC.
As mentioned above, it is also possible to adjust the flash from the camera body on many digital cameras, which makes perfect sense, since the sensor that is controlling the flash is located there.
Canon labels their newest TTL flash system, E-TTL II, which stands for Evaluative TTL version 2. Nikon’s Creative Lighting System is called i-TTL for intelligent TTL. Both have the ability to control a flash on-camera or off in one-third stop increments (EV=0.3) for very fine tuning of the flash’s exposure.
Of course, Olympus digital cameras have TTL too, as do Sony and some older Minoltas, as well as Pentax, Panasonic, Sigma, Ricoh, Fuji and just about every modern camera made. Through The Lens flash control has become a standard feature for all modern flash/camera systems.
One thing that needs to be mentioned here, is that you cannot put a Canon E-TTL flash on a Nikon body (or any other model) and use it in TTL mode. The contacts used are located in different places on the hot shoe. Also to use remote wireless TTL you’ll need a flash made by the same manufacturer as your camera.
However, it is possible to find third party flashes that work in TTL mode when mounted on your camera. Metz, Sunpak, Vivitar, Osram and etc. all make TTL flashes with different feet for different makes of cameras. They used to make one style flash and you bought the “foot” that you needed separately. It was called an SCA flash adapter. Now they make the same model flash with different feet molded on. If you go this route, be sure the flash is labeled for your camera type. You can get a TTL capable flash for around $100 USD if you purchase one from a company that makes flashes exclusively.
Modern TTL camera/flash systems also take into account the focal length of the lens, the focus distance and the chosen focal points when shooting in AF mode. If a vario-focal length, or “zoom” lens is mounted, then the focal length on the zoom is used.
Many new flashes have little computers. The new Nikon SB-900 automatically adjusts its output to the format of the imaging sensor and even has a way to do a firmware upgrade. They have come a long way from simply looking up at the film and shutting off at the right time. In many ways the new flashes are as advanced as the camera itself, and is why they cost quite a bit more than their predecessors.