Can someone please explain TTL in basic terms?

[EspressoJunkie]

I posted a thread in the lighting section asking about a flash for my 40D.

The term TTL has cropped up. I've googled it, but Im still not really sure about what exactly it is!

Can someone please explain in laymans terms, and aslo advise me on whether its worth spending extra on a flash to get it?

Thanks

 

[happygolucky]

Flash trigger.

 

[unplugged]

Any good?

http://en.wikipedia.org/wiki/Through-the-lens_metering

 

[EspressoJunkie]

Thanks for the replies.


So is it worth paying a bit extra for in a flash?

 

[vectraturbo]

if you are not used to using a flash manually then yes

 

[HoppyUK]

Thanks for the replies.


So is it worth paying a bit extra for in a flash?

Essential. All but the very cheapest guns (like v basic £50 Yongnuos) have it anyway.

 

[EdBray]

Flash trigger.

?????

TTL is just an acronym for Through The Lens and in flash terms it means that when a TTL compatible flash is fired by the camera the amount of light coming through the camera is measured and when the correct amount of light is received the processor in the camera sends a signal to the flash to stop and the full flash output is curtailed.

Canon DSLRs use a slightly different form of TTL which has the acronym ETTL or ETTL2 depending on both your camera body and the flashgun used.

ETTL just stands for Enhanced Through The Lens flash metering. What this means is that a Canon camera with an ETTL flash attached will use it's processor to send additional information to the flash unit such as the lens in use, the aperture selected and the distance that the lens is focused on. This allows the flash supplied by the ETTL gun to be more attuned to the particular situation.

ETTL2 is just an update to ETTL.

 

[Mike Jackson]

I'm going to get all pedantic now. E-TTL actually stands for Evaluative Through The Lens metering.

 

[Clickawaymedia]

Just hijacking this thread... I understand TTL, but My camera also offers ADI metering... Whats the difference?

 

[Flash In The Pan]

Just hijacking this thread... I understand TTL, but My camera also offers ADI metering... Whats the difference?

Clicky

 

[Ste Manns]

Edbray's explanation is correct, but if you want a simpler explanation here it is.

Basically in Ettl mode your flash will fire a pre flash, the camera will see this pre flash, magic will happen and then the flash will fire the actual exposure flash at a correct power level required, taking into account your camera exposure settings, the lens used, distance to the subject etc etc.

It's basically an automatic mode. A lot of people will tell you that its not great but personally I find Ettl (and in particular, wireless Ettl) fantastic, in certain (but not all) circumstances.

If you want to get into portraiture for instance, it would be very worth buying an Ettl flash, even better two, (or one and the Canon transmitter, or a long Ettl cord etc) so you can take advantage of wireless Ettl.

I took this pic using wireless Ettl:

The flash providing the exposure was outside on a stand, shooting through a glass door. I had my 580EX2 on camera acting just as a master/commander. Instead of going back and forth adjusting the flash power I could change the exposure on the camera's lcd. This allowed me to concentrate on capturing the shot - Julia moves fast and if I'd shot with manual flash I would not have got a shot at all. Alright this is just a messing about shot nothing special, but it illustrates the usefulness of Ettl/wireless Ettl quite well.