TTL is a term which describes light metering done ‘through the lens’ of the camera and different camera brands have come up with their own ways of using TTL for an automatic flash system.
In the old days of film cameras, TTL flash worked by measuring the amount of light hitting the actual film during the exposure itself.
In modern digital cameras, TTL metering had to switch to a slightly different system since there was no more film.
Now, newer modern forms of TTL flash works with a pre-flash system and E-TTL is just one branded name for this process.
E-TTL is Canon’s name for this technology whereas Nikon uses I-TTL and Pentax uses P-TTL)
The camera will measure the amount of light entering the camera when the pre-flash is fired and then base the actual flash output off of that reading.
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What Is E-TTL /E-TTL II?
E-TTL stands for evaluative-TTL or ‘evaluative through the lens’ and it is a Canon branded technology that they use in their flashes.
It is basically a form of TTL flash system they use in their digital cameras and E-TTL II is just a newer version of E-TTL flash.
E-TTL flash was first introduced in 1995 while E-TTL II was introduced in 2004 so unless you have a really old camera then your Canon camera and flash will be using the E-TTL II system.
A TTL flash system is a system that can be seen as the equivalent of an auto mode on your flash.
Just like with camera modes, it can make your life easier in certain situations but you also sacrifice some control over your exposure in return.
So Canon E-TTL / E-TTL II are just modern versions of TTL flash technology under the Canon brand.
Misconceptions Of TTL Flash Vs E-TTL
Due to the purpose of the old TTL flash systems and the modern TTL flash systems (like E-TTL) it’s very common for people to use the term TTL flash when they are referring to E-TTL / E-TTL II flash (or any of the other camera brands’ modern TTL flash systems).
My Speedlite Flash Is Set To TTL But It Won’t Work With My Camera!
This problem can occur partly due to the misconception I just described where people use TTL and E-TTL interchangeably as if it is the exact same thing.
The reason your Canon camera might not be working with your flash set to TTL mode is because your camera is most likely only able to use Canon E-TTL metering.
Flashes do still have TTL compatibility since some cameras are made to be compatible with both E-TTL and TTL flash metering.
These cameras tend to be film cameras and you won’t really find old school TTL flash metering in modern digital cameras.
This enables the compatible film cameras to use older flashes that only use TTL as well as newer flash units like the Canon speedlite EX series which use E-TTL.
How Does E-TTL / E-TTL II Work?
When taking a photo with E-TTL flash enabled this is what happens:
- The camera will meter the ambient light in the scene.
- Just before the real flash fires the flash unit will fire a ‘pre-flash’.
- The camera will compare the readings of the ambient light and the light from the ‘pre-flash’.
- The camera will use complex algorithms to communicate with the flash unit to tell it to fire the flash at a certain power which it deems to be ‘the best’ flash setting for the ideal exposure.
Is E-TTL / E-TTL II Flash Necessary?
If you’re comfortable with lighting and using manual flash settings then E-TTL flash is not necessary.
It can be useful in situations where the lighting changes quickly and you can’t constantly be changing your settings – think events like weddings or parties.
Besides these situations, E-TTL mode may actually become a hindrance to you as you will be giving up some creative control with your exposures since the camera and flash will decide what it thinks is the “best “ exposure.
You might not always agree with what the camera thinks is the ideal exposure.
Beginners, on the other hand, can find it useful if they are uncomfortable with using flash since it takes some guesswork out and still lets you get decent exposures.
Can I Use E-TTL Flashes In Manual Flash Mode Too?
If you want to use an E-TTL flash unit and also want to have the freedom to use manual flash settings, then you’re in luck.
It’s as simple as changing the mode on your flash unit from E-TTL mode to manual mode, then you can have full control over your flash settings.
E-TTL vs I-TTL vs P-TTL
As I said earlier, E-TTL is just a pre-flash TTL system and E-TTL (evaluative-TTL is Canon’s name for it.
I-TTL stands for Intelligent-TTL and it’s the name that Nikon uses for this type of technology.
P-TTL stands for Preflash-TTL and it’s the name that Pentax and Sony both use for this type of technology.
One thing to keep in mind is that each camera brand tends to only allow it’s TTL flash technology to be used with it’s own cameras.
For example a Canon flash on a comaptible Canon body can make full use of manual and E-TTL flash settings.
But if you tried to use a Canon speedlite flash on a Sony A7 camera, then you would only be able to use manual flash settings.
TTL VS E-TTL Video Explanation
This is a great video that explains the differences between TTL and E-TTL in an easy to understand way.
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