In my last blog post, I explained three things that affect exposure when using flash.
- Flash Power—The bright flash 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 set it, the darker it gets. Of course, this assumes your Flash Power and ƒ-stop is 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 camera’s sensor. The TTL flash is a very sophisticated flash system that 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. The first flash happens so fast that it looks like one flash went off to the human eye.
An incident meter is the most accurate way to take a reading for any photo. An incident reading 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 incident meters have an available light setting and flash setting where you can measure the light.
TTL metering is a reflective reading. You are reading the light that bounces off the subject. If you take a reflective reading of a White Wall, an 18% Gray Wall and a Black Wall, all three photos will look like an 18% Gray Wall.
Using the settings, you get from the incident reading meter for all three walls 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
If 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 an incident reading and then taking a photo may be impractical to get the “moment.” Roaming photos is where a flash with TTL can get you close on exposure and white balance. You may have to check the LCD for a histogram and adjust the EV of the camera and the flash. A histogram often is much more practical than incident reading.
The TTL will adjust pretty quickly when the subject moves toward you, like a person on a red carpet walking toward you. If you are shooting RAW, you most likely be close enough to fix it in post if necessary.
Most seasoned pros have TTL flashes, hot shoe flashes, and some studio strobes that are not TTL. In addition, most pros will have an incident flash meter to adjust the lights and camera.
If you do portraits in a studio setting, TTL flash isn’t necessary, but if you shoot pretty fluid situations, then the TTL system can help you get photos that may be impossible without them.