The TTL sensor tracks the amount of light emitted from the flash onto the film surface during exposure; the camera's light meter is not used to calculate exposure.
Matrix balanced fill-flash* TTL
In this mode, the camera's matrix metering adjusts exposure to ambient light, and the TTL sensor adjusts exposure during flash. This is done to balance the light from the flash so that it does not overexpose the subject in the foreground. Pre-flash and lens distance information are not used. 'Spot' and 'centre-weighted' options for balanced fill flash are available, depending on the selected camera metering mode.
* Balanced Flash: In this mode, the camera uses both the TTL flash sensor and the camera's light meter to balance the exposure of the foreground and background. The resulting exposure gives the greatest possible natural balance.
Multi-sensor 3D TTL balanced fill flash
The flash emits a series of pre-flashes just before the first shutter curtain opens. Test pre-flashes are detected by the TTL sensor mounted on the camera, analyzed for brightness and contrast, and then combined with distance information from the 'D' or 'G' lenses required for the feature to function. This mode is called 3D because the final exposure is calculated from the camera's light meter, monitoring pre-flashes, and distance information provided by the lens.
This mode adapts to most shooting situations, including bright subjects, off-center subjects, and small subjects far from the background.
Multi-sensor TTL balanced fill-flash
Works similarly to 3D multi-sensor balanced fill flash, but unless a 'D' or 'G' lens is used, no distance information is transmitted. There are two Multi-Sensor Balanced Fill-Flash modes, one using monitoring pre-flashes and the other not; The choice of mode depends on the flash and lens used.
Automatic balanced fill flash
This is a general term for automatic control flash power to balance the brightness between the foreground subject and the background using the TTL multi-sensor (see diagram below for the '5-segment TTL multi-sensor' diagram).
TTL flash sensor
5-segment TTL multi-sensor system
The picture on the left shows the latest multi-sensor flash (sensor with five red segments). The sensor is located under the mirror and is aimed at the film (or at the shutter), which measures the amount of light reflected from the film (or, in digital cameras, from the shutter).
A microlens above the sensor directs light from five areas of the frame onto it, and the light information is then sent to the camera's processor, where it is used to calculate exposure.
TTL - what is it? TTL stands for Time to Live. That is, the lifetime of a packet allocated to it at the moment of transition from the initial node to the final one. The IPv4 standard allocates an eight-bit header field to reflect TTL. Passing through numerous nodes to the destination, the value of the packet decreases by 1 unit each time. This is done in order to limit the time of its presence in nodes to a specific number. And this, in turn, avoids congestion in networks.
What happens if the TTL reaches zero? The packet will disappear, and the sender will receive a message that its time to live has expired, which means it needs to try again. The maximum value that an eight-bit field can reflect is 255. There are default values for operating systems. For example, TTL in Windows is 128, and in Linux and derivatives - Mac, Android - 64.
The DNS environment has its own TTL, and it reflects the relevance of the cached data. But this article will not be about him.
What is TTL used for and in what areas?
The package lifetime is actively used by various Internet providers, for example Yota. By doing this, they are trying to limit access to excessive traffic consumption when distributing Wi-Fi. This occurs due to the fact that the packet, moving from the device receiving traffic to the distributing device, reduces the TTL; as a result, the value received by the provider is less or, in the case of Windows, more than expected.
For example, we can describe the process of operating a smartphone based on Android. The device sends a request to receive data from a specific site. Along with it, a TTL is sent, the value of which is 64. The provider knows that this is the standard packet lifetime figure for this device, so it freely allows it to access the Network.
Now the device starts distributing Wi-Fi and becomes a kind of router. The connected smartphone runs on the Windows platform, and its TTL, passing through the distribution device, will be 127. The provider will encounter this packet and understand that its Internet is being distributed. Therefore it will block the connection.
Possibility of changing TTL on various devices
Changing the packet lifetime value can be useful to bypass traffic blocking by your provider. For example, if the cable connection is disconnected, and the user urgently needs to access the Internet from a computer. Then the smartphone becomes an access point and connects the PC to the network.
It is worth noting that some providers block access not only by TTL, but also monitor site visits. And if the resource is not connected in any way with the smartphone, i.e. it is not needed, the connection is terminated.
You can change the TTL in several ways, which will be described below.
Changing TTL on Android devices
The most in a simple way changing the lifetime of a package on Android devices will use a specialized software. For example, a very effective product is TTL Master. It can change the lifetime of the distributing machine packet to that obtained as a result of the data passage. For example, when distributing Wi-Fi to a Windows device, you need to set the value to 127, and to 63 on Android or Linux.
The program is free and can be easily found in the official Google Play store. However, it requires root privileges on the device to function.
The program interface is simple - the current value of the parameter is displayed at the top. Below are blanks for Windows and other operating systems. You can also set the desired value manually. Just below there is a button with the ability to go directly from the application to the modem settings. In some versions, a solution is available via iptables, for which there is a specific item.
In the settings it is possible to set the launch and change of life time automatically when the device boots. Some versions of Android allow you to launch the access point immediately after changing the value. There is support for the Russian language.
The application is constantly being developed and improved. There is a profile on github where anyone can branch and add their own features to the project. If the developers accept them, they will be included in the next release.
You can also try the method of manually modifying system files to change the package lifetime value. To do this you will need root rights. First you need to switch to airplane mode, that is, make the phone lose the Network.
Then use any explorer that can edit files. In it you need to follow the path proc/sys/net/ipv4. In this directory, you are interested in a file called ip_default_ttl. It contains the value 64, which needs to be changed to 63.
Next, you need to take the phone out of airplane mode so that it registers with the Network again. Now you can distribute wireless Internet and try to connect a device based on iOS or Android, that is, with TTL 64.
If you need to use a Windows PC as one of the clients, you will need to set a constant value for the packet lifetime in the manner described below.
Changing TTL on a computer with Windows operating systems
If you need to distribute the Internet from a smartphone running Windows, you will have to slightly adjust the registry values. This method will be relevant when the phone does not have root and it is impossible to bypass the lock on it.
You can launch the registry in the line of operating systems through the “Start” menu item “Run”. In it you need to enter Regedit and click OK. Two areas will appear in the window that opens. The left one contains the tree structure, and the right one contains the values. You need to find the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters branch. For Windows 8, Tcpip can be replaced by Tcpip6.
In the window with values, you need to create a new one. This is done by right-clicking the mouse. From the context menu, select New, then a new DWORD value, and name it Default TTL. What is this? This will be a static parameter for a constant lifetime value. Then right-click again and select "Edit". The number type must be decimal, and the value must be 65. Thus, the system will transmit a packet lifetime of 65, that is, one more than that of Android. That is, when passing through a smartphone, it will lose one unit, and the provider will not notice the catch. After making changes, you need to restart your computer.
Now you can distribute the Internet on Android without using special software and devices.
Change on Linux
How is TTL changed on a computer running Linux operating systems? For Linux, changing the packet lifetime is changed with one line in the terminal: sudo iptables -t mangle -A POSTROUTING -j TTL --ttl-set 65
Changing the packet lifetime on modems
You can change the TTL of the modem by changing the IMEI. It's such identification code, unique for each device that has access to cellular networks. The problem is that there is no universal method. This is due to the fact that each individual modem must have its own firmware, which will change the IMEI.
The 4PDA website has a selection of solutions for changing the lifetime on modems from different manufacturers and models. You can also find detailed implementations of this task there.
Changing package lifetime on iOS
Using the TetherMe tweak you can change the TTL to iOS. deb application that unlocks modem mode on devices with iOS on board. The fact is that Apple allows some operators cellular network block the "Modem mode" function at the SIM card level. This application allows you to activate it and use your phone as a modem.
Changing TTL on MacOS
MacOS has a default lifetime of 64. If you need to change it, you need to enter the command in the terminal: sudo sysctl -w net.inet.ip.ttl=65.
However, with this approach, the value will change back to 64 after a reboot. Therefore, it is necessary to perform a number of manipulations. At the root of the disk there is a directory etc. It's hidden, but you need to get into it. There the sysctl.conf file is created. You only need to write one line in it - net.inet.ip.ttl=65. And of course, save it.
To display this hidden folder in Findere, go to the main drive and press the key combination cmd+shift+G. In the window that appears, enter the name of the folder you are looking for, after which it will be found.
conclusions
There is such a thing as a USB TTL converter. However, it has nothing to do with the context of the article, and should not be confused with the lifetime of the package. A USB TTL converter is a kind of adapter for creating connections between USB devices and TTL logic.
The article explained in detail about TTL - what it is and what it is needed for. Several ways to change it will allow you to bypass traffic blocking restrictions on some providers. This makes it possible to use the Internet everywhere.
The implementation differs on different devices; this can be done either using software or by manually changing system files. Some modems will have to be flashed, each with its own software version.
Using these instructions, you can bypass the blocking of many providers that provide Internet access via a cellular network.
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TTL- Through-the-lens - through the lenses (English) - flash operating mode, also often called automatic mode, because The flash itself, with a preliminary pulse, determines the power of the pulse to take a photograph. Those. The built-in flash metering sensor, or the camera's built-in metering sensor, determines the power of the pulse when taking photographs.
To put it even easier, then TTL mode removes part of the work from the photographer. For example, we are photographing some event. We install (attach) the flash, configure the camera (aperture priority). Turn on the flash, TTL mode. That's all, the rest we need to do is change only the flash head (and only if desired). The flash automation itself will select the impulse strength, adjust the flash zoom, etc. depending on the camera settings ( , aperture, shutter speed, etc.) and shooting conditions.
Here you need to remember that you should not close the aperture too much, because The flash power may not be enough to illuminate the room. Therefore, I recommend that when photographing with flash indoors, try to open the aperture as much as possible and raise the ISO a little. Then we can bomb good reporting series in TTL mode...
Today, there are several types of TTL modes:
- simple TTL— camera metering is used without a preliminary pulse
- automatic TTL— preliminary pulse, then automatic selection of settings to adjust flash power
- estimated TTL- the most popular type of flash metering today. The pre-pulse that calculates the settings is completed in a fraction of a second, and is often not even visible to the naked eye. Before each main flash pulse, evaluative TTL exposure metering will fire.
Each flash manufacturer comes up with different acronyms for their TTLs. Nikon has i-TTL, Canon has A-TTL, E-TTL, E-TTL II, etc. In general, the essence does not change. The main thing is that the camera works correctly with this system.
The presence of a built-in TTL flash, for example Yongnuo, will work correctly on Canon cameras, but on Nikon cameras it will only manual mode. Therefore, if you are buying a non-branded flash, then check with the seller for which system it is intended. So, for example, a flash (non-TTL, manual) works equally well on both Nikon and Canon cameras. Because impulse strength, zoom, etc. we set it up manually, using the buttons on the flash itself.
So, in summary, TTL is undoubtedly a bigger plus than a minus. Especially if we're talking about about reportage shooting, where there is simply no time to set up individual devices. Another issue is that TTL and branded flashes are expensive, so I recommend paying attention to manufacturers such as Yongnuo, SIGMA, etc. Prices here are almost two times lower than company prices. The main thing when purchasing is not to confuse the systems and tell the seller that you have a Nikon D7000 camera, or a Canon EOS 650, etc.
We were working on location during which we photographed performer Mindy Gledhill and her tour bus. It was a beautiful sunny day, so one side of the bus was fully lit. This provided us with an excellent opportunity to test the performance of our Profoto B1 and B2 off-camera flashes in TTL mode.
TTL is an abbreviation for "Through-The-Lens" flash metering. By installing either the Air Remote TTL-C or Air Remote TTL-N on the camera, the photographer can configure lighting, turn them on and fire to get the perfect exposure using your flashes. Then, with the press of a few buttons, the photographer can adjust TTL exposure compensation directly on the camera itself, and when working with different groups, can increase and decrease the power of these individual groups (A, B, C) regardless of the camera in TTL mode or manual mode.
LIGHTING SCHEME
Our main lighting setup included a B2 with an off-camera softbox (OCF Softbox 2x3) as the main light, another B2 with a zoom reflector to light the hair, and two B1 off-camera flashes to light the shadowed side of the tour bus behind Mindy. . Additionally, to make sure we had complete control over the lighting of our subject, we used a gold/white folding reflector as a flag to shade her from the sun. Our main light and hair light were set to the left to match the direction of the sunlight. The background lights that shined onto the bus were installed only to subtly fill the shadow at the front of the bus.
TTL MODE
Our first flash shot was taken entirely in TTL mode with no flash exposure compensation. Our lighting fixtures were divided into three groups. A: main light. B: Light falling on hair. C: Background lighting at the front of the bus. Even with the extremely bright deceptive light coming from the bus, the first TTL shot was very close to what we needed. The main light was perfect and the hair light was 2/3 of a stop brighter than I would have liked. The only group that didn't suit me was the background lighting at the front of the bus. It was technically correct that the flashes tried to match their exposure to the rest of the bus, but this resulted in the front of the bus being too bright to look like a natural shadow. But ultimately, the Profoto AirTTL System created a very accurate initial exposure. Which now had to be adjusted according to our preferences.
SWITCHING TO MANUAL MODE
The Profoto Air Remote TTL-C system allows full TTL control and manual flash control in three groups (A, B and C), and manual flash firing in three additional groups (D, E and F). In our lighting scheme, only the first three groups were used. After our first test shot, we assessed the resulting image and determined that some manual adjustments were needed. So we switched the Air Remote TTL-C from TTL mode to manual mode and began making our adjustments by pressing the up and down buttons on the remote remote control for groups. Hair Light Group B was 1/3 of a stop too bright, so we pressed the power down button three times (each press corresponded to a 0.1 stop reduction). Our Group C bus background light was 2 stops too bright, so we pressed the power down button twice, holding it down long each time (each long press represents a full stop). Once the settings of each flash in the respective groups were changed at our command via the remote control, we began shooting. The results were exactly what we wanted.
CONCLUSION
Using the B1 and B2 off-camera flashes in TTL mode makes the lighting testing phase of a shot incredibly efficient. After receiving the initial exposure calculation via TTL, I quickly switched the Air Remote TTL-C to manual mode and made the necessary power adjustments. And lighting decisions are then made during the shooting process. I now find myself using TTL in some way on almost every shoot I do because TTL helps me get my bearings faster and allows me to spend more time and attention on other aspects of the shoot.
E-TTL (English: Evaluative-Through The Lens) — modern technology EOS flash system, based on completely different principles, and used with both digital and film Canon cameras belonging to group “A”
The basis of the technology is the measurement of the preliminary pulse of the main flash lamp reflected from the scene being photographed, the power of which is known in advance. The optional infrared emitter module in EX series flashes does not take part in exposure metering, but is used only for AF-assist illumination and control of external flash units.
An important difference from the previous A-TTL technology is the moment the measurement begins: if in old flashes the rangefinder was triggered when the shutter button was pressed, then in new flashes a preliminary pulse is emitted immediately before the mirror is raised.
The interval between the measuring and working pulses of the E-TTL flash is so small that both are perceived by the eye as one common one. In this case, instead of an additional camera sensor that captures light reflected from the film, a main TTL exposure meter is used, designed to measure constant light. Canon digital cameras use only this technology, since TTL OTF systems are ineffective due to the low reflectivity of photo matrices.
The main advantage new system is the measurement of flash light with the main TTL exposure meter, which makes it possible to carry out center-weighted or matrix metering of pulsed lighting with the same accuracy as continuous lighting. In addition, the evaluative metering algorithm takes into account the active AF point, giving priority to the area surrounding it.
Preliminary measurement occurs through the lens and automatically takes into account most factors that are inaccessible to an external sensor: the magnification of the installed light filter, the extension of the lens and its field of view. The system's operating sequence contains several stages, and begins with measuring the exposure of continuous light when the shutter button is pressed. After pressing it completely, a flash measurement pulse is emitted, the reflected light of which is also measured by a TTL exposure meter. The measurement result is used to calculate the power of the working pulse, the value of which is stored in the microprocessor memory. As with the A-TTL system, the aperture value is selected based on a comparison of continuous and pulsed light measurements.
When there is a sufficient level of continuous illumination, the “fill flash mode” is activated, reducing the pulse power by 1/2 - 2 steps to maintain a natural cut-off pattern. Immediately after the measuring pulse, the mirror rises and the shutter opens, and the flash emits a pulse in accordance with its power value recorded in the processor memory, calculated before shooting.
E-TTL was first implemented in 1995 in small format Canon camera EOS 50 and EX series flashes, which are partially backward compatible with previous generation cameras designed for EZ flashes. The first digital camera to support the system was the Canon EOS D30. Film cameras Canon, belonging to group “A”, like digital ones, support the E-TTL system, which has completely replaced A-TTL. EX-series flashes also provide fast sync and emit modeling light in a series of short bursts. The latter function is used to visually assess the light pattern obtained from additional flashes of the same system, controlled remotely via an infrared channel.
Disadvantages of E-TTL
The main disadvantage of the E-TTL system is the presence of a preliminary flash pulse, to which the people being photographed can react. Despite the short interval between flashes, it is quite sufficient for a person to blink and appear in the picture with his eyes closed, especially when synchronizing “by the second curtain”. The same problem applies when photographing wild animals. The effect can be prevented by using the flash exposure memory (Flash Exposure Lock, FE Lock, FEL), which emits a measuring pulse at the moment it is turned on. In this case, only the working flash is fired at the time of shooting.
Another problem is associated with the use of a light synchronizer for slave studio flashes and flash meters, which are triggered by a measuring rather than a working pulse. As a result, the slave flashes fire before the shutter opens, and the flash meter produces a measurement error. The problem is eliminated by the use of improved light traps that are triggered with a delay or from the second pulse.
E-TTL II
E-TTL II (English Evaluative-Through The Lens 2) - for 2016 latest technology Canon camera-flash interaction, first introduced in the Canon EOS-1D Mark II in 2004. Unlike basic system, E-TTL II uses all available matrix metering zones, and also takes into account the distance to the subject obtained from the lens focusing ring position sensor. The flash power calculated based on the guide number and focusing distance is used to correct the value obtained by measuring the pre-flash, eliminating gross errors when shooting small objects against a distant light background. It also prevents errors when the shot is recomposed after the lens has been focused, which occurs due to the priority of the selected focus point in flash metering.
The influence of bright reflections on measurement accuracy is also virtually eliminated.
Distance is not taken into account in three cases: when rotating the flash head for bounce photography, in macro mode, and when using additional flash units. Most people transmit information about the focusing distance to the camera. Canon lenses EF, but there are exceptions, such as the Canon EF 50/1.4 USM and the early version of the Canon EF 85/1.2 L USM.
System support depends only on the camera model: all EX series flashes are suitable for operation in E-TTL II mode.
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