What is TTL Flash? | TTL vs. Manual Flash
Great photography requires capturing light in just the right way. Effective lighting helps capture key components while minimizing distractions. It creates drama and interest in a scene that might otherwise be flat and boring – or it will soften and lighten a harsh scene. Lighting is one of the most important parts of any photograph.
Sometimes you have to work with the light available to you. If you are shooting landscapes, for example, you have no choice but to rely on nature. However, for many types of photography you can manipulate your lighting. In order to do so, you might choose a continuous light source (such as a lamp, a bank of fluorescent lights, or a pro LED) or some sort of flash or strobe (either a speedlight or a monolight).
When you are looking at flashes, there are two primary types that you can choose from: TTL flashes and manual flashes. But what exactly is a TTL flash and how is it different from a purely manual flash?
TTL vs. Manual Flash
All flashes, whether small speedlights (sometimes also called “flash guns”) that connect to your camera’s hot shoe or full-sized studio strobes (also called monolights), are either only manual or use TTL (or more recently ETTL) with a manual option. Both types of flashes have their advantages and disadvantages.
What is TTL Flash?
TTL stands for “Through The Lens” and is a metering system that controls the power of the flash based on exposure settings as determined by the camera. TTL flashes go back decades and have largely been replaced by ETTL (Evaluative Through The Lens) flashes, although many people still just shorten ETTL to TTL despite their technical differences.
Both systems will automatically set the flash power to ensure “proper exposure” (as determined by the camera) and take exposure settings such as shutter speed, aperture, and ISO into account. You can also use them in both manual and automatic exposure modes.
In order to get the most creative flexibility out of a TTL flash, shooters can combine the camera’s exposure compensation with the flash’s built-in flash compensation to manipulate the lighting ratios. For example, you can lower your camera’s exposure compensation while raising the flash compensation. This will darken the overall image, but illuminate the subject because the flash stays at a higher exposure. Note that the metering mode of your camera will also affect the performance of the metering of your flash, as anything that changes your camera’s exposure settings will have a cascading effect on your lighting. See Important Camera Settings: A Guide for New Photographers for more.
ETTL vs TTL
While both TTL and ETTL let the camera determine the flash strength, they do so in different ways. Original TTL flashes read the exposure of the overall image straight from the camera’s built-in exposure meter and set the flash strength off of that reading. By contrast, ETTL first fires a few flash bursts to read the exposure while the flash is lighting up the subject. Doing so gives ETTL a few advantages.
ETTL flashes can adjust for different shooting conditions. If the subject is closer to or farther from the flash, they will be exposed differently and ETTL systems can adjust for this. Similarly, if you are bouncing the flash off of a wall or the ceiling, the amount of light getting to the subject can change from shot to shot. This is not a problem with ETTL.
Because of the advantages of ETTL, almost all modern flashes use it. If you are using an older flash, though, make sure you pay attention to whether it is ETTL or a true TTL.
What is Manual Flash?
While TTL flashes will determine and set their power from shot to shot, manual flashes require the user to set the output power and will keep that setting until the user changes it. Generally speaking, this is notated as a fraction of the maximum power output. A power setting of 1/1 is the brightest the flash can be set. From there, power settings decrease until they reach their minimum power output which is often 1/64 or 1/128 power.
One thing to keep in mind with a manual flash is that often the camera won’t interface with it aside from telling it when to fire. This means that any automatic exposure mode on the camera will force the exposure to what it considers properly exposed with no consideration for the light coming from the flash. If you are using a manual flash, you will almost certainly want to be shooting in the manual exposure mode, or at a minimum using the exposure compensation feature.
Should You Use a Manual or a TTL Flash?
As stated before, TTL and manual flashes each excel in certain scenarios.
Because of their rapid adaptability, ETTL flashes should be used any time the flash power has to be quickly and repeatedly changed. Perhaps the best example is photographing wedding receptions or other events where you are moving around, bouncing flashes off of a variety of surfaces, and constantly changing the distance between you and the subject. While it’s possible with enough practice to be able to adjust a manual flash on the fly, in many situations it simply won’t be practical.
On the other hand, if your approach is to start with no light and systematically dial in a variety of flashes to achieve precisely your desired effect, you need to take full manual control. These shooting conditions are incredibly common when in a studio. Manual flashes can also be ideal for shooting outdoor portraits when you have time to set up and refine the ratio of exposure between ambient light and your flash.
Of course, there are other advantages and disadvantages to both manual and TTL flashes. If budget is a concern, manual flashes can be incredibly affordable compared to some TTL flashes. On the other hand, TTL flashes provide a more robust set of features. Additionally, all TTL flashes will allow you to turn off the automatic settings and take full manual control yourself, giving you the option to use either approach depending on your situation.
Keep in mind that TTL systems are often proprietary to the camera model, so a Canon flash’s ETTL isn’t going to be interchangeable with Nikon’s. Similarly, remote firing triggers with TTL compatibility will often be brand-specific. Folks who love using a variety of different cameras while using the same flash type will benefit from manual models.
Generally speaking, if you shoot a lot of events or moving subjects, spring for the ETTL-compatible flash systems that go with your camera ecosystem. If you are a studio shooter, or shoot mainly static portraits or product photography (and especially if you’re on a budget), you will do quite well with aftermarket manual-only flashes.
For many photographers, bringing artificial lighting into their toolkit, particularly through the use of flashes or strobes, is a pivotal step towards achieving their photographic vision. Photography is all about light and being able to take complete control of that light is empowering.
Whether you choose to shape the lighting with manual flashes or use a more dynamic approach by taking advantage of a TTL (or ETTL) flash system, a good flash will open up a new world of images for you.
And if you’re not sure about diving in and investing in a flash, you can always rent one or two and start experimenting with their possibilities.
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