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What Is a TTL Flash? TTL vs Manual Flash Modes

Flash photography is daunting for beginners. But the list of technical specifications on each flash can feel even more intimidating. What is TTL flash anyways?
Flashes, sometimes also called speedlights, have two different modes. These are TTL flash or Through The Lens, and a manual mode.
Each option has perks and disadvantages. Some professional photographers will stick exclusively with one, others will use both.
One is easier to use, one (mostly) gets much better results. Dig into TTL and manual flash with this quick beginner’s guide.

What Is a TTL Flash?

A photographer contemplating a shot - ttl vs manual flash
TTL stands for Through the Lens. Consider this flash mode the equivalent of that automatic mode on your mirrorless or digital camera.
A TTL flash will automatically use the camera’s built-in metering system and the distance to the subject (based on the focal point) to determine how much light to put out. This is sometimes called TTL metering or TTL flash metering.
Many TTL flashes will use a quick pre-burst of light before the actual flash to measure how much flash to use. But this pre-burst fires quickly and close enough to the actual flash that many don’t even notice it.
Using that information and the camera’s metering system, the flash chooses a power setting for you.
For companies selling flashes, TTL is often listed high in the product description. A flash without TTL can’t make automatic adjustments and relies entirely on input from the photographer.
TTL flashes tend to be pricer than manual-only flashes. But most flashes today have a TTL option. The difference between an inexpensive TTL flash and an expensive TTL flash is often light output and features like high-speed sync.
Like auto mode on your camera, TTL flash is easy to use. But also like the auto mode on your camera, TTL flash is difficult to customize. Because the settings are adjusted for you, it’d difficult to adjust the lighting from one shot to another.
A flat lay of various photography equipment
TTL flash isn’t completely impossible to adjust. Just like you can use exposure compensation on a semi-automated mode on your camera, TTL flashes have what’s called flash compensation too.
Flash compensation will take that automatic level set by the flash, and add more or less like. Just like exposure compensation, flash compensation is measured in fractions of a stop.
A -3 flash compensation will turn the flash down just a bit. A +1 will add a full stop of light more to the image.
Flash compensation is an excellent tool for photographers that are new to flash. And for  shots where the distance to the subject changes quickly. But it’s not as customizable as full manual flash mode.
Some TTL flashes have several TTL modes. On a Canon flash, for example, the A-TTL mode uses a pre-burst of light to determine the best flash output. And it uses the information to help the camera set the aperture.
In E-TTL or Evaluative-TTL, the camera measures the light without the flash and the light with the pre-flash. It then uses information from the two readings to determine the flash settings.
E-TTL is similar, but the results are weighted. This is better for photographing shiny or white subjects.

Using Manual Flash

A photographer taking a photo using manual flash instead of ttl
Like the manual mode on your camera, manual flash will offer the most control over your images. With manual flash, the photographer chooses the amount of light the flash sends out. Regardless of what the camera settings are.
Manual flash power is measured in fractions. A 1/1 setting is the most possible light that flash can send out. A 1/2 is half that, a 1/4, a quarter and so on.
Different flash models will have different flash ranges. Some will power all the way down to 1/64, some to 1/128, others to 1/250.
By controlling the flash power, you can customize the look of the light and shadows in the image. Flashes can often be used at the lowest possible setting. This is just to add a bit of fill light and a catchlight for portraits.
Flashes aren’t often used on full power. But a 1/1 flash can be used to backlight rain, to create dramatic hard light, or to light a subject that’s far from the camera.
Mastering manual flash takes practice and patience. Unlike the built-in meter on your camera, the flash doesn’t have a built-in meter to suggest a setting on manual mode.
A photoshoot using a ttl flash
Manual flash is instead learned by practice and experimentation. Many photographers have a go-to setting for each type of image. They can then raise or lower the flash from there as needed.
Another option is to use a handheld light meter to read the light in the scene. You can use that data to determine your correct exposure and flash settings. Handheld meters will allow for more exact use of handheld flash
Some photographers find it just as easy to start with a basic flash setting and fire a picture. They then adjust the flash settings higher or lower based on that first image.
Manual flash mode isn’t the only way to control flash. The camera’s exposure settings also impact the flash system. Narrowing the aperture will create an effect similar to lowering the power of the flash. The light on the subject will appear dimmer.
If the flash power remains the same, adjusting the aperture will impact the brightness of the flash.
To balance the flash with the rest of the photo, the shutter speed needs to be high enough to let the ambient or existing light in. If your subject is well-lit but your background is dark, you need to decrease your shutter speed. The shutter speed should be set to properly expose the background while also keeping the subject sharp.
Note though, that you can lower the shutter speed a little bit lower than what you’d shoot without a flash. This is because flash will help to freeze fast subjects too.
Atmospheric portrait of a dancer
ISO’s impact on flash is easy to remember because it’s the same as using ISO without flash. Adjusting the ISO makes the photo brighter or darker, impacting the ambient light in the background just as much as the light on the subject from the flash.
If the subject and background are well-balanced but the entire image is too dark or light, adjust the ISO only. The subject and background will remain balanced.
The light from a flash will always be more powerful close to the flash. And less powerful the farther you get from the flash. On manual mode, moving the flash farther away or the subject farther away is a simple fix for a flash that’s too bright.
That’s even more true when using off-camera flash. You can move the flash farther away and shoot the same composition as before you moved the flash.
Flash can be further controlled using flash modifiers, like softboxes and diffusers. Shooting with an unmodified flash creates hard light with harsh shadows. Using a diffuser or a softbox together with a lower flash power will create a softer, more flattering light. (I use and recommend the MagMod diffuser).
Flashes can also be bounced off a neutral-colored wall or ceiling, or by using a bounce card to soften the light. Bouncing the flash off a wall will create dimensional lighting. Almost as if you had placed the flash where that wall is instead of on the camera.

So What’s Better? TTL Flash Vs. Manual Flash

A photography flat lay of camera bodies, flashes and lenses
So if TTL flash is like the auto mode on your camera, you should always shoot in manual mode, right? Not so fast. Each flash mode has a unique set of pros and cons. You might use TTL for one scenario and manual for another.
TTL flash is excellent in scenarios where the distance between the flash and the subject changes fast. If you are photographing a wedding processional on manual flash mode, as each bridesmaid walks towards you, they will appear brighter and brighter and eventually be overexposed.
Using TTL and dialing down the flash compensation for a less harsh light will adjust the flash for you as the distance between the subject and the flash changes.
Manual flash is best in scenarios where you want the most control over the light source. And the distance between the subject and the flash doesn’t change rapidly.
Manual flash can also be fine when shooting moving subjects if the flash is on a low power. Such as using a 1/128 setting for a bit of catchlight and contrast.
Remember that adjusting the aperture changes the amount of flash that appears in the photo. In TTL, the flash will automatically adjust as you change the camera settings.
A portrait of a female model in low light
In TTL mode, it’s difficult to re-create the same lighting pattern twice, because you don’t know exactly what settings the TTL mode decided to use for you.
Photographers who understand manual mode often stay in that mode a majority of the time. They switch to TTL only when they can’t change the flash settings fast enough for the way the subject is moving.
If you’re annoyed that your flash is making dark shadows behind your subjects, manual flash and a diffuser will make a dramatic difference in your images.
But, TTL still has a place for beginners and moving subjects. Especially when used with flash compensation and a flash modifier. TTL is good for getting your feet wet with flash and sticking with a simple flash compensation to adjust the flash up or down.

Conclusion

TTL’s automatic flash adjustments have a place with moving subjects and photographers new to flash. But more often than not, manual flash mode will produce better results.
Understanding manual flash is only one piece of the puzzle, however. You should also understand how to use a diffuser, how exposure settings impact your flash, and for the most versatility, how to use off-camera flash.
We have a great post on using a ring flash to check out next!

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