What does flash TTL mean?

What does TTL mean? What does TTL in the camera mean? Let's take a look at the flash TTL in the camera.

Flash TTL

TTL is used to refer to any flash system that uses ThroughHelen (ThroughTheLens) to measure exposure.

TTL- The light passes through the lens and is reflected by the film, and the flash sensor continuously measures the light during the exposure until the correct exposure is obtained. This system is called TTL flash metering system.

Later, it developed into A-TTL and D-TTL in the digital age.

At present, Canon uses E-TTL and Nikon uses i-TTL, both of which are concrete manifestations of TTL.

Introduction to flash TTL

Historically, the development of TTL is divided into two stages: the built-in TTL metering component of the camera and the flash with TTL function. Interestingly, almost 15 years after the release of the built-in TTL in the camera, the TTL flash appeared. The appearance of TTL brings the greatest convenience to users, that is, even when shooting in a hurry, it is too late to estimate the distance and adjust the aperture, and there will be no big deviation when using the flash, which makes news photography and other work more convenient.

1963 the first TTL photometric camera

From external measurement to internal measurement

The full name of TTL is ThroughHelen, which means through Helen. Before TTL, camera photometry mainly relied on Cds (cadmium sulfide photoresistor) outside the fuselage, which was easily affected by ambient light and could not reflect the light loss caused by light passing through multilayer lenses or filters, which easily led to underexposure. The metering element of TTL is located inside the fuselage, close to the negative/sensor position behind the lens. Because it measures the light passing through the lens, the accuracy of TTL photometry is better than that of external photometry.

Let's start with the history of TTL cameras. In fact, there is still controversy about the world's first camera using TTL metering system. Because in the 1960s, several camera companies, including Topcon, Nikon and Pentax, successively introduced cameras with TTL metering. Pentax put forward this concept before 1960, but it was not until 1964 that Spotmatic was officially mass-produced. On the contrary, Topcon took the lead with 1963, slightly ahead.

Pentax is introduced into 197 1, which means electronicshutter. It is the first SLR camera in the world whose shutter speed can be controlled by TTL system. Because of electronic control, it becomes a stepless shutter, which breaks through the preset limit of the original mechanical shutter, such as the speed of 1/53 seconds or11300 seconds, and improves the exposure accuracy. But Pentax did not further develop this concept, and introduced a flash with TTL. About seven years later, in 1978, Olympus launched the world's first TTL flash T32, and the TTL metering flash system officially appeared.

From automatic measurement to TTL measurement

The original flash cannot change the output, and every flash is full output. If the distance between the subject and the camera changes, it is necessary to adjust the aperture to control the receiving amount of the flash, so as to obtain appropriate exposure. Later, an automatic flash lamp with an external photometric element appeared, and the output of the flash lamp can be controlled according to the light receiving degree of the main body. As for the method of controlling the light quantity of the flash, it is to control the on and off time of the flash. The flashing time is only between11000 and110000 seconds. When the shutter is opened, the flash is output at the same time. When the metering module thinks that the amount of light reflected by the object is enough, it will stop the flash output in the middle of exposure when the shutter is still open. Then the exposure of the subject is completed by flashing lights. As for the exposure of the background environment, it is mainly determined by the opening time of the shutter.

However, the automatic flash also has the problem of measuring light outside the camera. If the lens is equipped with a filter, it will affect the accuracy of flash output. After the appearance of TTL flash, because we can get data such as aperture and subject brightness from lens photometry, we can truly reflect the amount of light needed, control the flash time more accurately, and save the trouble of calculating aperture and distance in the past. Modern flashlights can even achieve zoom linkage, which is helpful to adjust the irradiation range and make the power supply more effectively used and not wasted.

For flashlights with external metering components, the output should be manually increased after installing the filter. TTL flash light metering is set in the fuselage, which can accurately output even if a filter is added, a jump light is used or even an off-board flash light is used.

However, it should be noted that, like automatic photometric exposure, TTL flash only provides normal exposure, which can be changed by flash compensation if necessary. General flash has 1/3 EV adjustment. Therefore, TTL is best used as a reference index for normal exposure, and will be changed when necessary, rather than monolithic.

On the other hand, when we set the camera to automatic exposure mode (such as P or Auto), the camera often fixes the aperture and shutter at a certain value. If you want to control the depth of field, the dynamic performance of the subject and the brightness of the background, you need to use the manual exposure mode.