What is TTL Flash and do I need it?

In my last blog post I explained there are three things that affect the exposure when using flash.

• Flash Power—How bright the flash is will influence if the picture is over, under or properly exposed. You can control the Neewer flash from 1/128 to full power in 1/3 stop increments.
• ƒ-stop/Aperture—You control how much of the light is coming into your camera by the camera iris called the aperture. These are fractions. The focal length of the lens over how wide the opening of the lens is. 
• Flash Distance to Subject—The closer you put the flash to the subject the brighter the subject and the further away you put is the darker it gets. This is assuming your Flash Power and ƒ-stop are constant. 

TTL—Through The Lens

TTL metering has been around for a while with cameras. Your camera helps make the proper exposure settings based on what light hits the sensor of the camera. The TTL flash is a very sophisticated flash system, which sends out a flash that tells the camera what to set the camera and then the flash fires again taking the photo at those settings. This happens so fast that to the human eye it looks like one flash went off.

The most accurate way to take a reading for any photo is using an incident meter. This is where you put the meter where the subject is located and take a reading of the light falling onto the subject. The white dome needs to be where the subject is to get an accurate reading. 

Most of the incident meters have a available light setting and flash setting where you can measure the light. 

TTL metering is a reflective reading. You are reading the light that is reflected off the subject. If you take a reflective reading of a White Wall, a 18% Gray Wall and a Black Wall all three photos will look like an 18% Gray Wall.

If you use the settings you get from the incident reading meter for all three walls then they will look like they should.

TTL Metering has a variable

As you can see the TTL metering system has one major disadvantage of using a reflective reading to set the aperture, shutter and ISO on your camera—the color and tone of the subject will influence the exposure and white balance whereas the incident reading is consistent.

Incident vs Reflective

As long as the situation allows you to use incident metering you will get the most consistent results. However, there are situations where this is impractical.

At parties where you are moving around the room getting a incident reading and then taking a photo may be impractical to get the "moment." This is where a flash with TTL can get you really close on exposure and white balance. You may have to check the LCD for histogram and make an adjustment to the EV of the camera and/or EV of the flash. This often is much more practical than incident reading.

When the subject is moving toward you quickly like a person on a red carpet walking towards you the TTL will adjust pretty quickly. If you are shooting RAW you most likely be close enough to fix in post if necessary.

Most seasoned pros have both TTL flashes, which are hot shoe flashes and some studio strobes that are not TTL. Most pros will have a incident flash meter to make the adjustments to the lights and camera.

If you just do portraits in a studio setting TTL flash isn't necessary, but if you shoot situations that are pretty fluid then the TTL system can help you get photos that may be impossible without them.

Off Camera Flash – Blog post 3 of 3

You can see the blur in the volleyball even with strobes being used due to the 1/250 sync limitation.

TTL Flash offers some advantages over manual flash. I use the Nikon speedlight system that has helped me have an edge over many other photographers not using the system.

There are three things that make me choose my Nikon Speedlights over the manual flash: 1) I have no sync speed limitations, 2) quick—I don’t have to pause to take readings and then set the camera, and 3) I can shoot at very wide opening f/stops.

You can see the blur of the basketball due to slow shutter speed with the strobes.

Unlimited sync speeds

When you can shoot at any shutter speed then you open the possibilities for so many things.

 
1. You can shoot at high shutter speed like 1/2000 or 1/8000 of second to stop the action.  You see when the shutter is open at 1/250 sec for manual flash there is enough movement is sports to have some motion blur.  You see this is hockey and basketball.
 
2. You can control the background—outside! You can crank that shutter speed up and underexpose the background by say 2 or 3 stops and then up you flash output 2 or 3 stops to properly expose a subject, yet underexpose the background.  Great to get those dark blue skies behind a subject.

The TTL flash easily figured the correct amount of fill flash on the fly here.

Fast

You don’t always have time in some situations to take the time to take flash readings and then set the camera.  News events are a good example where you need to be ready.  Recently I photographed the founder, president and son of the president for an article.  These folks are known to change their mind at the last second and ask you to photograph them just about anywhere—this is when having a TTL portable flash let’s you adjust on the fly.

Taking a flash into the rain forest where coffee is grown in the mountains of Mexico lets me pull it out under all the shade to make the photo look like sunlight.

Wide-open f/stops

Many photographers today are shooting with an f/1.4 lens.  If you go outside to shoot you cannot use a manual flash because shooting at f/1.4 means you will have to shoot at a very high shutter speed.  The TTL high-speed sync lets you shoot with a flash. 

To be able to shoot large groups outside you need those high f/stops that will often require the manual flash.  To be flexible and use high sync shutter speed you need the TTL system.  What I hope you now know is there are advantages to both systems.  Don’t buy both systems right away.  Buy one and learn how to use all the advantages of the system.  Once you find you cannot deliver photography to clients because the system you have is limited—buy the next system and learn all it can do.