What is flash TTL mode. The Complete Guide to On-Camera Flash. TTL - flash control

Today again about the outbreak.

Photo tricks. Part 9. Taken with I-TTL BL FP SB-900

I will explain a little how the flash works in automatic mode. Usually, automatic flash mode has a TTL prefix in its name. It stands for very simple - Through the lens - through the lens (through the lens). This means that the flash output is adjusted using the light that has passed through the lens.

This is done quite interestingly: the flash gives a test pulse of light. Typically, the power of such a pulse is 1/128 of the full power of the flash. The light from the flash bounces off what we are photographing, passes through the lens and hits the meter's sensors. The sensor transmits the power value luminous flux camera processor. The processor thinks for a long time, analyzes, and calculates what should be the power of the main flash pulse. The processor knows that the first pulse had a power of, say, 1/128, while the exposure meter received values ​​that do not satisfy the exposure by 3 stops, therefore, the processor makes it clear to the flash that the main pulse should be 3 stops more powerful, and correspond to 1/1 16 flash power. This way we get a pretty shot with the correct exposure.

The most interesting: in modern digital control centers, the probe pulse is practically invisible. It feels like the flash immediately gives the right pulse of light. But this is not so, in TTL modes, the pulses go very, very quickly, one after the other in a series in strobe mode. The human eye and human reaction hardly notice the test impulse.

The test pulse is often called " preflash". There can be many preflashes, not just one, and their intensity can be different. To be honest, I don't know how much power my Nikon preflashes have,. For Nikon, the delay between the probe and the main pulse is on the order of 0.4 s.

With flash. TLL through umbrella, light blur from command impulses

Important: in ordinary digital cameras, the exposure metering system is not so well thought out, and the processors are not so powerful, and the flashes cannot fire a large number of "volleys" at the same time, therefore, I easily notice preflashes on ordinary digital cameras (soap dishes). Also, the test or control pulses of the built-in and external flashes of my cameras and flashes are very clearly visible when working in a creative lighting system.

While working in TTL mode, I came across a couple of interesting features:

1. Many people have a very quick reaction, and when photographing with a flash, they begin to squint at the first impulse, and the main one "draws" them in the picture with narrowed eyes.
2. Pre-flashes fill the background with unnecessary light, this often gives blur (blurring) in the eyes of people. Nobody needs extra reflections.
3. This way the flash heats up faster and uses more battery power.

To overcome this ailment, TTL is enough to use flash in. With manual control of the flash output, there is no test firing and the flash will immediately fire the main flash. The beauty of this mode is that:

1. Blinking of the eyes is completely eliminated. The pulse of my Nikon flash has a duration from 1/800 to 1/40.000, during which time not a single person will have time to blink. Yes, the person blinks, but after the flash, and the light of the flash lamp "draws" a person with open eyes on the photograph.
2. Blur in the eyes decreases. In studios, everyone works with manual power control flashes, there is practically no problem with blur in the eyes. True, there is another problem, the lighting devices themselves are clearly visible in the eyes, often rectangular in shape, which makes human eyes look like the eyes of cats (not natural).
3. Recharging lasts faster, no extra energy is wasted. Perhaps even the guide number increases, since the entire dose of light is supplied at once.

These are the advantages of manual flash control.

TTL is the lifetime of a data packet in the IP protocol. How can TTL interest a regular user? Surely, most of you ended up on this page in order to find out how to bypass the restrictions on the distribution of the Internet from your smartphone. TTL control is used by mobile operators to detect traffic from an unauthorized connected device. From this review, you will learn exactly how TTL helps the provider learn about the distribution of the Internet using Wi-Fi or USB and how an ordinary subscriber can outwit a greedy operator. We will try to explain clearly what TTL is and how this value can help subscribers.

How TTL works

Unfortunately, unlimited Mobile Internet is not currently provided by any operator without any restrictions. There are tariffs that provide for the absence of restrictions on speed and traffic, but when using a SIM card only in a smartphone. Also, you cannot share the Internet with other devices. If you turn on a Wi-Fi hotspot on your smartphone or connect to a laptop via USB, the operator will instantly record this fact and take appropriate measures (offer to pay extra). Many are perplexed about what kind of technologies allow the provider to calculate the distribution of the Internet. In fact, everything is much simpler than it seems. In order not to allow subscribers to share the Internet with other devices, the operator only needs to control the TTL. For example, if you turn on the modem mode on the phone, the TTL outgoing from the connected devices will be 1 less than that of the smartphone, to which the provider will immediately react. TTL manipulation allows you to bypass the restriction on tethering.

If you still don't understand what TTL is and how it works, check out the infographic below.

The device works without distributing the Internet.

For iOS and Android devices, the default TTL is 64. If the phone does not distribute the Internet to other devices, all packets go to the operator with a TTL value of 64.

The device distributes the Internet.

When trying to distribute the Internet using Wi-Fi, Bluetooth or USB to other devices, for example, a laptop and another phone, packets from the distributing device still leave with a TTL value of 64. Packets from the computer / laptop to the Internet distributor reach the Internet device with a TTL value of 128 (the default value for Windows), lose one on the distributor device and go to the operator with TTL = 127. Packets from the receiving Internet phone reach the distributor with TTL = 64 and go to the operator with TTL = 63, having lost one unit. For the operator, this means that the subscriber distributes the Internet, as evidenced by packets with three different TTL values. As a result, the provider takes appropriate measures in relation to such a subscriber.

The device distributes the Internet with TTL adjustment.

To prevent the operator from calculating the fact that tethering has started, it is necessary to change the default TTL on the Internet distributor so that packets from other devices, if they lose one of the TTL, have the value that was set for the “default” distributor. The above picture shows that after the adjustment, the TTL value on the distributing Internet phone is 63. iOS and Android devices have TTL = 64, but after the packets pass through the distributing device, the TTL loses one and goes to the operator with a value of 63. It turns out that the operator does not see nothing suspicious and the subscriber can distribute the Internet without any restrictions and additional payment.

If the Internet receiving device has a default TTL not 64, you need to make the appropriate changes. For example, if you want to distribute the Internet to a laptop or computer that has TTL = 128, you need to change it to 64. This scheme allows you to simultaneously distribute the Internet to a computer, as well as iOS and Android devices... If for some reason you cannot change the TTL on the PC, then change the TTL of the distributor to 127. As a result, packets will go to the operator with the same value and no suspicions will arise. However, such a scheme has a drawback. You will not be able to connect iOS and Android devices to the Internet simultaneously with your computer if their TTL is not 128 by default.

The device distributes the Internet with TTL correction and fixation.

This scheme is the most convenient. You need to change and fix the TTL for any outgoing packets. That is, it does not matter at all which devices will connect to the Internet. This option will be ideal for those who cannot change the TTL on the receiving device, such as smart-tv or game consoles. The disadvantage of this method is that it is not suitable for all phones.

Conclusion

We hope you understand what TTL is and how adjusting this value can be useful for an ordinary subscriber. We tried to explain everything briefly and easily. If you still have questions, ask them in the comments and we will try to help you. As a reminder, this overview is intended to give you an understanding of TTL. As for the practical ways to change this value, they are all described in a separate article.

By adding one or two flashes to your arsenal of special equipment, you can significantly expand the creative possibilities of your camera. This publication contains the most important information on the nuances of using the various flash functions and some tips for putting them into practice.

Technique

There are a lot of manufacturers producing flashes for cameras. There are models designed for installation only in a hot shoe, there are more massive options - exclusively for studio shooting. It is worth dwelling on the first group in more detail, since such flashes in skilled hands allow you to effectively control many functions of modern cameras.

The key is to select the correct flash model for your particular camera to mount on a dedicated hot shoe. For example, Canon offers the original Speedlite EX line of flashes, and Nikon offers the SB Speedlight series. In addition, there is the concept of a "lead" or "top" flash. Such a model is able to control the work of the remaining (additional) models by controlling them.

For Canon The flagship is the 580EX (discontinued) and 580EX II.
For Nikon- SB-800, SB-700, SB-900.

It is worth noting that the range of flashes of these leading companies is quite wide, but only the top models act as the leading ones. Outbreaks junior level eg Canon 430EX II and Nikon SB-600 can be used wirelessly only as slaves.

Cameras are available with a built-in flash capable of controlling external, for example, Nikon models D700 and Canon EOS 7D. This is convenient, especially if you already have an external flash. Thanks to this function, it can be successfully removed from the hot shoe and continued to operate from a distance. To find out if the camera has the ability to use the built-in flash as a master, just read the instructions.

Exposure control

There are three methods of exposure control:
1. Change of parameters.
2. Change of parameters.
3. Change of value.

Flash adds a fourth option - you can now control exposure by adjusting personal auxiliary lighting. This is convenient because it saves the photographer from having to rely on natural light at the shooting location. Of course, no one forbids the use of all kinds of screens, reflectors and diffusers, but that's a completely different story.

The main functions of modern flash units will be examined using the examples of the Canon Speedlite 580EX II and Nikon Speedlight SB-900 models. Detailed guidance on their use is presented in the instructions, so further we will focus only on the key features.

TTL - flash control

TTL stands for Thru the Lens. This measurement system is implemented in almost every digital camera. Speaking of specific manufacturers, Canon offers an algorithm called E-TTL, and Nikon offers i-TTL. The principle of their operation is similar: special sensors built into the camera measure the conditions of a specific shooting location, for example, lighting parameters, chromaticity, and others. This process takes place precisely through the lens.

Based on the processing of the information received, the camera "communicates" its conclusions to the photographer, warning him that the scene is too dark or too light for a particular combination of shutter speed, aperture and ISO settings. If the automatic mode is used, the camera makes the necessary adjustments on its own. In manual mode ("M") the photographer will have to do this.

A flash that supports TTL also receives information about the lighting in the scene. By analyzing this data, it calculates the required power of the light pulse. This indicator can be entrusted to the automatic mode, but it can also be adjusted manually. Even in automatic mode, the owner can adjust the flash as desired based on the TTL metering results. This is exposure compensation directly with the flash.

Flash exposure compensation is provided by controls identical to those of the camera system. The exposure value (EV) can be adjusted for both the built-in and external TTL-compatible flash.

The photographer can control the flash from anywhere using a standard 5-stop exposure scale. You can set the parameters to the same value (EV), you can use a value higher or lower.

Undoubtedly, the TTL-metering flash exposure compensation function is convenient enough, a great way to quickly and very accurately balance the ratio of natural light to flash light in a given shooting situation. There are many options, but the main guideline is the quality image that the photographer needs. For example, you can adjust flash compensation to 2/3 EV to fill in the shadows as desired without affecting the tones or even midtones.

The flash can also serve as the main light source, it is advisable when its power is clearly higher than the indicators of natural light, or a ratio of 50 to 50 is observed. In a word, focusing on the scene, you can adjust the flash as required and make the frame more interesting.

Exposure Bracketing

The principle of Flash Exposure Bracketing (FEB) is almost the same as in-camera (AEB). The mode allows the user to select a preferred power step, such as 1/2, 1/3, or even a whole step. If you experiment, you can easily see that shots with different lighting conditions differ significantly from the flash.

When working with on-camera system flashes, the most correct method of exposure metering is measuring the light transmitted through the camera lens (from the English. Through the lens — "Through the lens"). In this case, all corrections for the aperture of the lens, used light filters and attachments are automatically taken into account, and the metering angle is also automatically matched to the angle of view of the lens. That's why modern systems flash controls are built precisely on the principle of TTL metering. Naturally, automatic TTL metering is not without its drawbacks, and each company, developing and improving its own flash control system, went its own way.

The Canon EOS system flashes are based on TTL technology, which includes a module with sensors located at the bottom of the inner space SLR camera... Sensors measure the illumination of the field of the frame at the time of shooting. As soon as the exposure (product of illumination and exposure time) of the field of the frame reaches a threshold value, the camera electronics interrupt the flash pulse.

Today there are three generations of the EOS flash system: A-TTL, E-TTL and E-TTL II.

A-TTL (eng. Advanced-through the lens) is the first implementation of the EOS flash system technology, first introduced in the 1986 Canon T90 camera. The principle of A-TTL operation is to use an additional infrared lamp mounted on a fixed part of the flash body. There is also a light sensor that measures the amount of light reflected from the subject after an infrared flash pulse.

The moment the shutter button is pressed, the infrared flash emits a pulse parallel to the lens axis. A sensor located on the flash measures the light reflected from the object and transmits the data (shutter speed and aperture) to the camera to calculate the exposure and power of the main flash flash. The camera, in addition, measures the overall illumination of the field of the frame without a flash (up to an infrared pulse).

The data obtained as a result of the two measurements are compared and, if necessary, the preliminary calculations of the exposure are corrected. After that, the shutter opens and exposure is performed. At this time, the main flash fires and TTL-sensors measure the illumination of the field of the frame based on the amount of light reflected from the film or matrix. At risk of overexposure, the flash pulse is cut off.

Disadvantages of A-TTL metering

If the object in the frame has a high reflectivity (for example, in the frame there is a person next to a mirror), there is a high probability of an error in calculating the power of the main pulse and exposure data. In addition, errors can occur if the main pulse is not produced directly into the subject, but into the ceiling or reflector. A-TTL flashes will not fire in super high-speed sync at shutter speeds faster than 1/250 sec.

E-TTL (eng. Evaluative-Through The Lens) - development of the EOS flash system technology, in contrast to A-TTL, which provides for the use of the main emitter for a preliminary flash. This significantly reduces the likelihood of errors in the calculation of exposure and flash power when using reflective surfaces, if the flash head is directed not at the subject. In addition, as with A-TTL, the camera's built-in sensor stops the flash if necessary.

To calculate exposure and power of the main pulse, the same sensor is used as for light metering in normal conditions (and not a separate one, as in A-TTL). E-TTL flash units operate in super high-speed sync at shutter speeds faster than 1/250 s, up to 1/8000 s (depending on camera capabilities). If, in normal sync mode, the shutter first opens completely, after which the flash exposes a frame with the shutter open, then in super-high-speed sync mode, the flash emits a high-frequency, time-stretched pulse that is longer than the time the shutter opens and consists of many short pulses. The total pulse power in this mode of operation is less than in the normal mode of operation.

The E-TTL metering sequence is as follows:

1) when half-pressing the trigger, the brightness is measured from constant lighting,
2) a low-power preflash turns on and the exposure sensors measure a new brightness value,
3) the value of the initial metering without flash is subtracted from the brightness measurement with flash,
4) at the moment the shutter is fully pressed, another measurement of the brightness from the ambient light without a flash takes place (to take into account the possibility of re-framing) and the required flash pulse value is calculated,
5) the exposure is made, the flash is fired.

When shooting in autofocus mode, exposure is calculated based on the position of the focusing area. In the case of manual focus, the focus is on the “brightest” area when calculating the exposure.

E-TTL first appeared in 1995 with the Canon EOS 50.

E-TTL II (eng. Evaluative-Through The Lens 2) is the latest camera-flash interaction mechanism to date, first introduced with the Canon EOS-1D Mark II in 2004. Unlike its predecessor, the E-TTL II uses all available metering zones and also takes into account the distance to the subject.

In E-TTL II, in addition to exposure data without and with an evaluative pulse, it also takes into account the distance to the subject, which is "reported" by the lens focused on the subject. Why is this needed? Here's one possible example. It may happen that the subject occupies a small part of the frame and the E-TTL will simply not take it into account and the entire exposure will be calculated for the surrounding background. And if the position of the object in space is specified, then the necessary correction will be made to the exposure.

A photo flash is a fairly convenient, effective and powerful tool that can significantly improve image quality. Use flash when light is not enough or on a bright sunny day to highlight deep shadows. Learning to use this correctly additional source light, you will open new world digital images.

Therefore, we propose to begin with understanding the operating modes of this device.

There are three main flash modes: auto(TTL, ADI, etc.), manual (manual) and multi.

As a rule, flashes have all of these modes of operation. But there are models that lack any or several of these modes. Let's see if all these additional features are really necessary when shooting.

Auto mode

In TTL mode (Nikon flashes - i - TTL, Canon - ETTL ), the flash settings are automatically adjusted.

TTL, or Through The Lens - "through the lens" means that, by adjusting the flash power, automatic exposure metering occurs by means of illumination in the frame of the lens lens. At the same time, the technique takes into account all the parameters of the lens used: its aperture ratio, viewing angle, filters.

When choosing a flash, be sure to pay attention to whether it supports the TTL ... There are completely manual models, as well as supporting earlier technologies than your camera. But this does not mean that they are not compatible. It's just that the capabilities of your camera will not be used 100%. The same thing happens when working on an old model of the camera with the use of an advanced flash.

Flash shooting in Auto mode is similar to that of the camera itself. The technique independently selects the flash output power and range. When using the auto flash mode, it is not at all necessary to set this mode on the camera.

Trusting the settings to the technique, remember that the equipment cannot take into account all the peculiarities of the shooting. Especially if the flash works for reflection. In this case, the settings are approximate.

TTL mode it is used, as a rule, by novice photographers or in the event that the subject is changing rapidly and there is no time to constantly think about the parameters, for example, when shooting reportage.

But even in automatic mode, you can edit the operation of the flash; for this, there are settings for its compensation. If it seems to you that the flash did not sufficiently illuminate the subject, you can always manually set the value (from -3 to +3) by which you want to compensate the flash output. A similar function is available for the built-in flash.

You can also control the flash through the camera settings. For example, if in difficult shooting conditions (for example, against the sun) you only need to highlight one part of the frame, choose partial or spot metering. This will allow you to evenly illuminate objects in the frame.

In order to achieve the desired lighting result in the frame, it is better to learn how to shoot correctly in manual mode, or to use flash power compensation correctly.

Manual mode

As the name implies, in this mode all settings are set manually. Basic settings include flash output and flash zoom.

The flash power is selected based on how brightly you want to illuminate the subject and at what distance the subjects will be illuminated by the flash.

Flash output is adjustable from 1/1 to 1/128 of maximum flash output depending on the flash model. Modern flash models are equipped with a display that shows the parameters you set. If there is no display, a scale with luminous lamps serves as an indicator of the set power. The more bulbs are lit, the more powerful the light pulse.

Another flash setting mode is zoom. He is responsible for the angle of propagation and the range of the pulse. In most cases, it is recommended to set the flash zoom value according to the focal length of the lens in use. When working with long-focus optics, the angle of view decreases, but the distance to the subject increases. Consequently, the pulse of light is required more powerful. In this case, the beam of light can be narrow and not illuminate the edges of the frame that are not involved in the plot.

Using wide-angle optics when shooting, it is necessary to illuminate a large area of ​​the frame. In this case, the objects of the image are at a closer distance. Therefore, the pulse of light should be counted on for a short distance.

When working with a flash that has only manual settings, it is necessary to learn how to properly control the light. The zoom setting, as mentioned above, can be set based on the focal length of the optics. Light pulse power parameters are selected experimentally.

First of all, the following parameters must be taken into account here:

- what time the shooting takes place and what are the lighting conditions (indoors or outdoors, in the morning or in the evening, etc.);

- what is the distance to the subject (the closer the subject, the less flash power is required);

- what are the exposure settings. Already using aperture, shutter speed and ISO you can adjust the amount of light around, and use the flash to illuminate the foreground. The pulse power can be in the range 1 / 16–1 / 64. Typically, these images come out more naturally;

- whether diffuse, directional or reflected light is used in shooting. The use of various diffusing nozzles reduces the intensity of the light flux, therefore, in this case, a more powerful light pulse is most often used.

ModeMulti

Unlike manual and automatic, in the mode Multi the flash fires several times during the shutter speed. This allows you to achieve very interesting results, because the same object is differently lit in the same frame.

Multi-mode requires full manual control. However, in addition to adjusting the flash and flash zoom, there are two additional parameters to be set here. This is the number of pulses and their frequency in Hz. The higher the frequency of flash pulses, the shorter the time interval between adjacent pulses will be.

Multi mode is not present in all flares. Its main purpose is to create certain lighting effects for specific or experimental photography. This mode is not needed for everyday work. Therefore, if this mode is absent in the settings of your flash, do not worry, it is not so, it means that it is necessary.

As you can imagine, an external flash is a powerful tool in the hands of the photographer. However, you still need to get used to working with it. Remember, perfect photos taken with an external flash may take some time. First you need to understand all the intricacies of this technique. If you have not yet decided which model of flash you should buy, which modes you need, you can always rent a flash unit!

Best regards, team photobuba. by!