A TTL question

Hi all,

I've been learning to use my flash for a while now, but virtually always in manual mode. And I'm getting the hang of it! I'm not so practised with TTL however. If I use TTL, but bounce my flash, am I right in assuming I compensate for the fact there's less light hitting the subject by using FEC? Does the camera make the decision on flash output assuming that the flash is pointing directly at the subject?

Thanks!

David

beegeeboy wrote in post #12212337
If I use TTL, but bounce my flash, am I right in assuming I compensate for the fact there's less light hitting the subject by using FEC? Does the camera make the decision on flash output assuming that the flash is pointing directly at the subject?

When you use TTL, it will send a pre-flash a split second before the main flash. That pre-flash is used to adjust the level of the main flash on the subject. The pre-flash gets bounced the same way as the main pop, so there is no need for you to try to adjust for the bounce or diffusion or modifier that you may be using.

With TTL, just use FEC to adjust the flash level if you want more or less of the flash effect that TTL is providing.

I posted this info earlier as I am learning from Neil Van Niekirk.
Go here for Bounce and then onto the BFT Black Foam Thingy.
http://neilvn.com …hniques/4-bouncing-flash/
http://neilvn.com …1/the-black-foamie-thing/
Get hold of his book from the library or buy it. I have read most of it and gained a good lot from it.
http://neilvn.com/tang​ents/about/book/
He explains everything with good expamples.

beegeeboy wrote in post #12212337
Hi all,

I've been learning to use my flash for a while now, but virtually always in manual mode. And I'm getting the hang of it! I'm not so practised with TTL however. If I use TTL, but bounce my flash, am I right in assuming I compensate for the fact there's less light hitting the subject by using FEC? Does the camera make the decision on flash output assuming that the flash is pointing directly at the subject?

Thanks!

David

TTL will compensate for light lost in bounce or through a modifier (up to the power limits of the light, anyway) - you only use FEC for taste if it's too much or not enough.

pcj wrote in post #12213674
TTL will compensate for light lost in bounce or through a modifier (up to the power limits of the light, anyway) - you only use FEC for taste if it's too much or not enough.

Moderator PaceAce and myself have proven in recent months that ETTL sometimes does fail to properly compensate for the use of certain modifiers!

We conducted carefully controlled tests with a pair of 5" x 7" Wescott MicroApolly mini softboxes, used on Canon and Metz flash units, with a variety of Canon bodies (both FF and APS-C), and a variety of lenses. We discovered that while ETTL handles flash bounce well without additional FEC, the results with softboxes can be quite divergent in results. In certain test conditions the shots resulted in UNDER exposure (what one might assume) but other test conditions resulted in OVER exposure. We have not been able to determine what is the variable that determines UNDER vs OVER exposure with softboxes, and would need to do more extensive testing to puzzle thru that question.

Wilt wrote in post #12214536
Moderator PaceAce and myself have proven in recent months that ETTL sometimes does fail to properly compensate for the use of certain modifiers!

We conducted carefully controlled tests with a pair of 5" x 7" Wescott MicroApolly mini softboxes, used on Canon and Metz flash units, with a variety of Canon bodies (both FF and APS-C), and a variety of lenses. We discovered that while ETTL handles flash bounce well without additional FEC, the results with softboxes can be quite divergent in results. In certain test conditions the shots resulted in UNDER exposure (what one might assume) but other test conditions resulted in OVER exposure. We have not been able to determine what is the variable that determines UNDER vs OVER exposure with softboxes, and would need to do more extensive testing to puzzle thru that question.

Oh, I don't debate that ETTL can sometimes fail to meter correctly - but from my experience it fails a lot less often than I fail when I'm shooting manually out in the field I'm usually more worried about my batteries failing than I am ETTL mis-firing - but of course, your mileage may vary.

I've been using ETTL with wireless off-camera flash controlled by my 60D pop-up for 6 months. Using either Lumiquest Softbox III or Cheetah Qbox 16, ETTL gets the exposure right most of the time. If I need to use FEC, it's never more than ±1EV. I think the reason that FEC is sometimes necessary is that I sometimes use the softbox for side (split) or partial back lighting, and ETTL uses a form of center weighted averaging for its exposures. I've never had to make more than one adjustment, however, so ETTL gets me quite close to begin with.

Thanks for all the replies-things much clearer now! And I like Neil N's black foam thingy...

So many very knowledgeable people on here!

David

pcj wrote in post #12214682
Oh, I don't debate that ETTL can sometimes fail to meter correctly - but from my experience it fails a lot less often than I fail when I'm shooting manually out in the field I'm usually more worried about my batteries failing than I am ETTL mis-firing - but of course, your mileage may vary.

Our experiments have not (yet) discovered a lack of consistency with any particular combination (body+lens+flash+modif​ier)...we HAVE discovered that ONE particular combination would be consistent in OVERexposing with a softbox on the flash, while a second particular combination might be consistent in UNDERexposing.

Analagous to saying. "My dad is always early, mom is always late" but being unable to jump to any particular conclusion about your cousin Albert being early or late in a consistent manner.

Wilt wrote in post #12216714
Analagous to saying. "My dad is always early, mom is always late" but being unable to jump to any particular conclusion about your cousin Albert being early or late in a consistent manner.

David