The TTL sensor monitors the amount of light emitted by the flash onto the film surface during exposure, the camera's exposure meter is not used to calculate exposure.
Matrix balanced fill flash* TTL
In this mode, the camera's matrix metering controls exposure based on ambient light, while the TTL sensor controls 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 'center-weighted' balanced fill-flash options 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 exposure meter to balance foreground and background exposure. The resulting exposure gives the greatest possible natural balance.
3D TTL multi-sensor balanced fill flash
The flash fires a series of pre-flashes just before the first shutter curtain opens. Monitor pre-flashes are detected by the camera's TTL sensor, analyzed for brightness and contrast, then combined with subject distance information from the 'D' or 'G' type lenses required for this function to work. This mode is called 3D because the final exposure is calculated from the camera's exposure meter, information from monitor 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.
TTL multi-sensor balanced fill flash
Operates similarly to 3D multi-sensor balanced fill-flash, but if a 'D' or 'G' type lens is not used, no distance information is transmitted. There are two multi-sensor balanced fill-flash modes, one using monitor pre-flashes and the other not; The choice of mode depends on the flash and lens used.
Auto Balanced Fill Flash
This is a general term for automatic control flash output to balance the brightness between the subject in the foreground and the background using a TTL multi-sensor (see diagram below for ‘5-segment TTL multi-sensor’).
TTL flash sensor
5-segment TTL multi-sensor system
The picture on the left shows the latest flash multi-sensor (sensor with five red segments). The sensor is located under the mirror and pointed at the film (or shutter) and 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, 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 the packet, allotted to it at the moment of transition from the initial node to the final one. In the IPv4 standard, an eight-bit field in the header is allocated 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 his presence in the nodes to a specific number. And this, in turn, avoids congestion in the networks.
What happens if the TTL value reaches zero? The packet will disappear, and the sender will receive a message stating that its time to live has expired, which means that you need to try again. The maximum value that an eight-bit field can represent 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 freshness of the cached data. But this article will not be about him.
What is TTL used for and in what areas
The packet lifetime is actively used by various Internet providers, such as Yota. Thus, they are trying to limit access to the consumption of excessive traffic when distributing Wi-Fi. This is due to the fact that the packet, passing from the device receiving traffic to the distributing one, reduces the TTL, as a result, the provider receives a value less or, in the case of Windows, more than expected.
For example, you can describe the process of a smartphone based on Android. The device sends a request to receive data from a specific site. A TTL is sent along with it, the value of which is 64. The provider knows that this is the standard digit of the packet lifetime 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 distributing device, will be 127. The provider will meet this packet and understand that its Internet is being distributed. Therefore, it will block the connection.
Ability to change TTL on various devices
Changing the packet lifetime value can be useful for bypassing traffic blocking by the provider. For example, if the cable connection is turned off, and the user urgently needs to access the Internet from the computer. Then the smartphone becomes an access point and brings the PC to the network.
It is worth noting that some providers block access not only via TTL, but also track site visits. And if the resource is not connected to the smartphone in any way, i.e. it does not need it, the connection is terminated.
You can change the TTL in several ways, which will be described later.
Change TTL on Android devices
by 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 dispenser packet to that which results from the data pass. For example, when distributing Wi-Fi on a Windows device, you need to set the value to 127, and on Android or Linux - 63.
The program is free and can be easily found on the official Google Play store. However, it requires root permissions on the device to function.
The program interface is simple - the current value of the parameter is displayed in the upper part. A little lower are blanks for Windows operating systems and others. You can also set the desired value manually. A little lower is a button with the ability to go from the application directly to the modem settings. In some versions, a solution is available through iptables, for which there is a specific item.
In the settings, it is possible to set the launch and change of the lifetime automatically when the device boots. Some versions of Android allow you to start the access point immediately after changing the value. There is support for the Russian language.
The app is constantly being developed and improved. There is a profile on github, in which everyone can branch and add their features to the project. If the developers accept them, they will be included in the next release.
You can also try the method of modifying system files manually to change the package lifetime value. This will require root rights. First you need to switch to flight mode, that is, make the phone lose the network.
Then use any explorer that is able to edit files. In it, you need to go along the path proc/sys/net/ipv4. In this directory, you are interested in a file named 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 on the Web 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 want to use a Windows PC as one of the clients, then you will need to set a constant value for the packet lifetime in the manner described below.
Change 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 is not rooted and it is impossible to bypass the lock on it.
The launch of the registry in the line of operating systems can be done through the menu item "Start" "Run". Enter Regedit in it and click OK. Two areas will appear in the window that opens. The tree structure is on the left and the values are on the right. 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 the values, you need to create a new one. This is done with a right click. Select New from the context menu, then a new DWORD value, and name it Default TTL. What's this? This will be a static setting 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 the packet lifetime of 65, that is, one more than 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 to Android without using special software and devices.
Change on Linux
How is TTL changed on a computer with 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 to each device that has access to cellular networks. The problem is that there is no universal way. This is due to the fact that each individual modem must have its own firmware that will change the IMEI.
The w3bsit3-dns.com 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 the lifetime of a package on iOS
With the help of the TetherMe tweak, you can change it to iOS TTL. deb application that unlocks hotspot 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 level. This application allows you to activate it and use your phone as a modem.
Change TTL in MacOS
MacOS has a TTL of 64 by default. If you want 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, a number of manipulations must be performed. The etc directory exists at the root of the disk. It is hidden, but you need to get into it. The sysctl.conf file is created there. You need to write only one line in it - net.inet.ip.ttl=65. And of course, save.
To display this hidden folder in Finder, go to the main drive and press cmd + shift + G. In the window that appears, enter the name of the desired folder, 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. 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 for. Several ways to change it will allow you to bypass the traffic blocking restriction on some providers. This makes it possible to use the Internet everywhere.
The implementation on different devices is different, you can do it both using software tools and manually changing system files. Some modems will have to be flashed, and each has its own version of the software.
These instructions 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 mode, often called automatic mode, because. the flash itself, with a pre-pulse, determines the flash power for taking a photograph. Those. the built-in flash metering sensor, or the camera's built-in metering sensor, determines the flash power when photographing.
To put it even more simply, TTL mode removes part of the work from the photographer. For example, we are photographing an event. We put (fix) the flash, set up the camera (aperture priority). Turn on the flash, TTL mode. All the rest we need to do is change only the flash head (and then if desired). Flash automatic will select the strength of the impulse, adjust the flash zoom, etc. depending on camera settings ( , aperture, shutter speed, etc.) and shooting conditions.
Here you need to remember that you should not close the aperture too much, because. flash output 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 reportage series in TTL mode...
Today, there are several types of TTL modes:
- plain TTL- camera metering is used without a preliminary impulse
- automatic TTL- pre-pulse, then automatic selection of settings for adjusting the flash output
- estimated TTL- the most popular type of flash metering today. The pre-pulse that calculates the settings takes a fraction of a second and is often not even visible to the naked eye. Before each main flash burst, TTL evaluative metering will be triggered.
Each flash manufacturer comes up with different abbreviations for their TTL. Nikon i-TTL, Canon A-TTL, E-TTL, E-TTL II, etc. In general, the essence of this 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 (without TTL, manual) works equally well on both Nikon and Canon cameras. Because pulse strength, zoom, etc. we set it up manually, with the buttons on the flash itself.
So, in summary, TTL is undoubtedly a big plus than a minus. Especially if we are talking 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 branded ones. The main thing, when buying, is not to confuse the systems, and tell the seller that you have a Nikon D7000 or Canon EOS 650 camera, etc.
We worked on a location shoot where we photographed singer Mindy Gledhill and her tour bus. It was a beautiful sunny day, so one side of the bus was completely lit up. This was a great opportunity for us to test our Profoto B1 and B2 off-camera flashes in TTL mode.
TTL is short for flash metering through the lens ("Through-The-Lens"). By attaching either Air Remote TTL-C or Air Remote TTL-N to the camera, the photographer can set lighting, turn them on and fire up to get the perfect flash exposure. Then, by pressing a few buttons, the photographer can adjust the 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 in manual mode.
LIGHTING SCHEME
Our basic lighting setup consisted of a B2 flash with an OCF Softbox 2×3 as the main light, another B2 with a zoom reflector for hair, and two off-camera B1 flashes to illuminate the shaded side of the tour bus behind Mindy. . Also, to make sure we had full control over our subject's lighting, 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 backlights that illuminated the bus were only installed to subtly fill the shadow in 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. Q: Light falling on the hair. C: Background lights in front of the bus. Even with the extremely bright deceiving light from the side of the bus, the first TTL frame was very close to what we needed. The main light was perfect, and the light on the hair was 2/3 stops brighter than I would have liked. The only group that did not suit me was the background lighting in 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 in accordance with 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 evaluated 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 started making our adjustments by pressing the up and down buttons on the remote remote control for groups. Hair light group B was 1/3 stop too bright, so we pressed the power down button three times. (Each press was a 0.1 stop decrease). Our group C for the backlighting of the bus was 2 stops too bright, so we pressed the power down button twice, long pressing it each time. (Each long press corresponds to a full stage). As soon as the settings of each flash in the respective groups were changed at our command via the remote control, we started shooting. The results were exactly what we wanted.
CONCLUSION
Using the B1 and B2 off-camera flash units in TTL mode makes the lighting test stage 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 the lighting decision is then made during the shooting process. These days, I find myself using TTL in some way for almost every photo shoot I take, 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 (Eng. Evaluative-Through The Lens) — modern technology EOS flash system, based on completely different principles, and used with both Canon digital and film cameras belonging to group "A"
The basis of the technology is the measurement of the light of the preliminary pulse of the main flash lamp reflected from the scene being shot, the power of which is known in advance. The optional IR emitter module in EX-series flashes does not take part in exposure metering, but is used only for AF-assist illuminator and external flash control.
An important difference from the previous A-TTL technology is the moment the measurement starts: if in the old flashes the rangefinder was triggered when the shutter release button was pressed, then in the new flashes the 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. In this case, instead of an additional camera sensor that captures the light reflected from the film, the main TTL exposure meter is used, designed to measure constant illumination. Canon's digital cameras only use this technology, since TTL OTF type systems are inoperable due to the low reflectivity of the photo sensors.
The main advantage new system is the measurement of flash light by the main TTL exposure meter, which makes it possible to carry out center-weighted or matrix metering of pulsed illumination with the same accuracy as continuous. In addition, the evaluative metering algorithm takes into account the active AF point, giving priority to the area around it.
The preliminary measurement takes place through the lens and automatically takes into account most of the 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 sequence of operation of the system contains several stages, and begins with the measurement of the exposure of continuous illumination when the shutter release button is pressed. After pressing it completely, a flash metering 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 in the A-TTL system, the aperture value is selected based on a comparison of continuous and flash light measurements.
When there is sufficient continuous illumination, the “fill flash mode” is activated, reducing the flash output by 1/2 - 2 stops 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 the value of its power stored in the processor memory, calculated before shooting.
E-TTL was first implemented in 1995 in a small format Canon camera EOS 50 and EX-series flash units, which are partially backward compatible with previous generation EZ flash-based cameras. First digital camera supporting the system was the Canon EOS D30. Film cameras Canon, belonging to group "A", as well as digital ones, support the E-TTL system, which completely replaced A-TTL. EX-series flash units also provide high-speed sync and emit modeling light in a series of short bursts. The latter function is used to visually evaluate the light pattern obtained from additional flashes of the same system, controlled remotely via infrared.
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 enough for a person to have time to blink and be in the picture with his eyes closed, especially when synchronizing with the second curtain. The same problem is relevant when shooting wild animals. The effect can be prevented by using the flash exposure memory (eng. 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 flash unit for slave studio flashes and flashmeters that are triggered by a measuring, and not a working, pulse. As a result, remote flash units fire before the shutter opens, and the flash meter generates a measurement error. The problem is eliminated by the use of advanced light traps, triggered with a delay or from the second pulse.
E-TTL II
E-TTL II (Eng. Evaluative-Through The Lens 2) - for 2016 latest technology Canon's camera-flash interaction, first introduced with the Canon EOS-1D Mark II in 2004. Unlike basic system, E-TTL II uses all available matrix metering areas, and also takes into account the distance to the subject received from the lens focus ring position sensor. The flash output calculated from the guide number and focusing distance is used to correct the value obtained by preflash measurement, avoiding blunders when shooting small objects against a distant bright background. In addition, errors are prevented when recomposing a picture after focusing the lens due to the priority of the selected focus point in flash metering.
The effect of bright reflections on measurement accuracy is also virtually eliminated.
Distance is not taken into account in three cases: when turning the flash head to shoot in bounce light, in macro mode, and when using optional flash units. Information about the focusing distance is transmitted to the camera by most Canon lenses EF, but there are exceptions such as the Canon EF 50/1.4 USM and the early Canon EF 85/1.2 L USM.
System support depends only on the camera model: all EX series flash units are suitable for E-TTL II operation.
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