# I need to understand ETTL better.



## e.rose (Mar 11, 2014)

Yup.

It's true.

I kind of understand what's going on, but I never really quite FULLY... figured it out.

I don't shoot on camera flash 90% of the time (I always have it off camera and use them on Manual with triggers), so I never... REALLY quite worried about it.

But the fact of the matter is... I really should understand it better.

SO. Does anyone have any SUPER CLEAR, and awesome resources explaining ETTL?

We're talking "Understand Exposure" level of clear... Like, I really need it super dumbed down for me so I can make sure I 100% understand this, and can make it work for me without having to think about it too much in a pinch.

THANKS.


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## Derrel (Mar 11, 2014)

This might be one of the better, clearly-written sets of explanations I've ever seen related to Canon flash. It is very clearly-written stuff. It's presented in 3 good segments, with bullet point headlines, so you can really see what there is to know, ahead of time, then just dive in.

Flash Photography with Canon EOS Cameras - Part I.


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## e.rose (Mar 11, 2014)

Thanks, I'll take a look at it


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## vimwiz (Mar 11, 2014)

Lets take a trip through the history of Canon TTL metering:

To begin with -  The T90 was the first Canon camera to support through-the-lens (TTL) flash metering. Metering was performed by the spot metering photocell beneath the main morror, allowing for off-the-film (OTF) TTL metering. This works by measuring the reflected light off colour film itself. It shipped with the Speedlite 300TL (Which also did Advanced TTL (A-TTL) which is the same except distance is calculated using a preflash infrared pulse and sensor on the flash body.). This allowed it to provide X-Sync at up to 1/250, and the T90 is the only non-EOS body compatible with current Canon flashes.

E-TTL (Evaluative-Through The Lens) was the version uses on EOSes.  It uses a visible pre-flash before the main flash in order to obtain a more correct exposure. It uses the normal, internal, evaluative metering sensor, as well as another external one fror the pre-flasn. More modern EOS bodies do everything in the body, and, like the T90+300TL did, uses distance information in its algorithm, and calculates where the subject lies in the scene itself, rather than relying on the AF points. This fixes issues early EOS bodies had with tricky seans featuring hotspots


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## Overread (Mar 11, 2014)

My experiences are that it generally works well for fill lighting, where you're just using it to bump up the shadows it will generally work without much trouble.  The only really important thing to keep in mind is that the cameras meter isn't going to take into account the flash light, so if you're using a semi-auto mode you're going to need decent ambient exposures or a lot of exposure compensation. 

It can do decently well as the main light contribution as well, but you've got to be shooting in manual mode to force the camera settings you want. I also tend to find there is sometimes a little fiddling around with exposure compensation here as well and you might find you need to push it up or down depending on the lighting (adjusting how it meters might also help although I'll admit to not tinkering with this aspect that much). 

I typically find that in bright/sunny conditions a little flash exposure compensation helps as well, dialling in a little negative exposure on the flash itself helps counter blown highlight problems (although in harsher lighting its hard to avoid them all). Remember flash exposure compensation is compensating the flash component of the lighting only. 



I find it pretty useful for general shooting and can be a bonus when your working distance to subject and ambient lighting shift around a fair bit (something I find with macro shooting). With more experience you might be able to get to akin levels of accuracy with manual power settings on the flash itself; its always a shame, in my  view, that the flash won't show the power output its used when in ettl on the back for reference*.


*though its also my understanding that it selects a lot of in-between power ratio settings when in ettl mode.


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## Big Mike (Mar 11, 2014)

In a nutshell...

E-TTL uses a preflash to determine how much light/power to use.  Before the shutter opens, it pops a small flash and reads how much is reflected back Through The Lens (TTL).  By doing that, you can shoot straight, bounce and/or use diffusers & filters etc., and the process will account for that.

Note that E-TTL metering doesn't use the camera's primary metering mode...it's completely separate.  So if you are in say, spot or partial metering mode, the E-TTL metering is still going to be 'Evaluative'.  You can change it to 'Average' but the recommended setting is 'Evaluative' for most scenarios.  

So the camera receives the light from the preflash and determines how much power it should use, to expose what it thinks is the subject, to a middle grey level.  In other words, just like the camera's ambient light meter, the flash metering will only expose correctly when your subject is the same tone as a grey card.  If the subject is brighter, the metering will under expose it.  If the subject is darker, the metering will over expose it.  

This is why you have FEC...Flash Exposure Compensation.  So when you are shooting someone like a bride in a white dress, the metering will naturally under expose, so in order to get proper exposure, you must dial in positive FEC.  It's pretty much the same principle as getting proper exposure with ambient light.  You can dial it on either the Camera or the Flash, I've always liked using the camera controls.  

The main issue with E-TTL, is that it's still an automatic function.  It tries to determine what your subject is, and tries to give you enough light to expose that subject to a 'middle grey' level.  It's metering will change when the brightness/reflectivity of the scene/subject changes.  For example, if you go from shooting a bride in a white dress, to a groom in a black tux, the TTL metering will give you different amounts of light.  
In other words, it can be inconsistent. 

But if you know and somewhat expect that it will sometimes be inconsistent, then it's still a great tool.


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## KmH (Mar 11, 2014)

You might find some of the info in this Canon specific book helpful:
Speedliter's Handbook: Learning to Craft Light with Canon Speedlites


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## runnah (Mar 11, 2014)

I am going with witchcraft and voodoo.


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## e.rose (Mar 11, 2014)

Big Mike said:


> In a nutshell...
> 
> E-TTL uses a preflash to determine how much light/power to use.  Before the shutter opens, it pops a small flash and reads how much is reflected back Through The Lens (TTL).  By doing that, you can shoot straight, bounce and/or use diffusers & filters etc., and the process will account for that.
> 
> ...



This actually makes the most sense to me.

Maybe it's the state of mind I'm currently in, but this made the most sense. 

I'm mostly curious about it in the setting of a reception hall.

When I'm forced to use on-camera flash in other situations, I usually still switch it to manual to keep things consistent. However, in a reception setting, when I'm moving about in the middle of a very tight crowd, flash on manual doesn't work. Because if I set it to light someone well 6 feet away from me, but then I'm suddenly 3 feet away from someone else and catching a moment that's happening, they're SUPER bright. ETTL helps in that situation, but then I deal with the very opposite problem. When I'm lighting for someone 3 feet away from me in a reception hall, but I see something happening 6 feet away I want to catch, they're super dark. I notice a lot of the time that there's usually someone on the edge of the frame with a white shirt who is light brightly, which made me start wondering what exactly the "flash" is seeing when it meters, because I assume the reason the people 6 feet away were dark is because, even though I had my spot meter pointed at them... the flash somehow took into account the dude on the very edge of the frame, closer to the camera, that had a white shirt on.

Basically I'm trying to figure out how to speak this damn thing's language so I can make it do what I want it to do when I want it to do it.





runnah said:


> I am going with witchcraft and voodoo.



I agree.


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## table1349 (Mar 11, 2014)

Derrel said:


> This might be one of the better, clearly-written sets of explanations I've ever seen related to Canon flash. It is very clearly-written stuff. It's presented in 3 good segments, with bullet point headlines, so you can really see what there is to know, ahead of time, then just dive in.
> 
> Flash Photography with Canon EOS Cameras - Part I.


Real nice..... steal the website I always recommend for these kinds of questions. :lmao:


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## pgriz (Mar 11, 2014)

Put up a set of those ropes that is used to keep people in line, tell people they can only walk between those sets of ropes, and you've got the distance problem licked - then manual flash will work each time.

Oh, ok.  Not a serious idea.  :blushing:

However, with ETTL, you DO need to know your maximum range to get a decent shot, which is ISO dependent.  So if you have a camera with high ISO tolerance, figure out the max. distance you can shoot and still get a good exposure, and then you know that its at that distance or closer that you've got to shoot.  It helps if there is enough ambient to allow the flash to be more fill than primary - so that you don't get the ghasty direct flash look.

Another technique that I have used in some locations, is to put up a set of manual flashes so that they illuminate the perimeter of the room, and then shooting anything inside that perimeter is usually possible using the manual flash settings.  Of course you have to be careful not to get the illuminated surface(s) visible in the picture, as it/they will show up as blown.


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## robbins.photo (Mar 11, 2014)

Ok, well if you really want to understand ETTL - your going to need a live chicken, a red candle and a white candle, the eye of a newt and some paprika. Hmm.. wait.. that doesn't sound right. Oh.. sorry, that's for a voodoo curse. Nevermind.


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## table1349 (Mar 11, 2014)

robbins.photo said:


> Ok, well if you really want to understand ETTL - your going to need a live chicken, a red candle and a white candle, the eye of a newt and some paprika. Hmm.. wait.. that doesn't sound right. Oh.. sorry, that's for a voodoo curse. Nevermind.



Nooooo......that was not a voodoo curse, with the paprika in it that was a love spell to get e.rose to marry you.  You need the *feet of a frog *not paprika for it to be a voodoo curse.  Jeeze did you flunk basic Voodoo 101 or what?


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## robbins.photo (Mar 11, 2014)

gryphonslair99 said:


> robbins.photo said:
> 
> 
> > Ok, well if you really want to understand ETTL - your going to need a live chicken, a red candle and a white candle, the eye of a newt and some paprika. Hmm.. wait.. that doesn't sound right. Oh.. sorry, that's for a voodoo curse. Nevermind.
> ...



Ok, well technically I didn't flunk Voodoo 101 - I got an incomplete.  The teachers eyebrows did grow back... eventually.   I don't think there is enough Paprika on the planet to convince E.Rose to marry me, she doesn't strike me as being that foolish.. lol.


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## weepete (Mar 11, 2014)

I just read the posts by vimwiz, overread and big mike as one continuous section. Great explination guys thanks!


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## Derrel (Mar 11, 2014)

Okay, the "NEW" Canon flashes use the E-TTL II protocol, which is supposed to be better than the earlier protocol, E-TTL, when using newer flashes like the Canon 580 EX II, the "II" meaning the newer, second-generation Mark II variant of that flash, and with the very latest RT 600 flash.

Newer Canon cameras, like the 7D, and the later EOS 1-series cameras, have color-evaluative light metering capabilities, whereas the earlier cameras were color-blind, and went STRICTLY by reflectance value (18% gray).

So, a few questions: in the early days of digital, I read about a LOT of very inconsistent E-TTL results with the pre-II flashes like the 580, and the "older" cameras.

But then, E-TTL II came out, and well, it was alleged to be better, and on the 20D and 5D, I found E-TTL flash with the 580 EX-II flash was sort of okay. What I am wondering now is how E-TTL II flash protocol, and an E-TTL II flash unit, work together with the color-aware, latest generation Canon bodies, like the 7D and 70D, and the 5D-III,and so on.

At one time, E-TTL flash was HYPER-SENSITIVE to the AF point that was in use, and the subject that was underneath that AF point. I'm wondering how much that is true today, with the latest flash and cameras, or if the focus point in use weighting is still as strong as it was, and if it's still as prone to blowing things out as it used to be, or if they've managed to get that issue more under control now that the newer bodies are measuring not just reflectance, but also are reading color values.


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## runnah (Mar 11, 2014)

Derrel I have had great success using the mark 3 and 600 ex rt in ETTL mode. In all camera mode it evaluates the scene and delivers great results.


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## table1349 (Mar 11, 2014)

robbins.photo said:


> gryphonslair99 said:
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Well there is that plus if my remember is working correctly ( at my age it don't always) e.rose is *MARRIED* already. 
	

	
	
		
		

		
			





  I realize that she is in Tennessee, but lessen you be her brother or daddy I doubt that you two could legally get hitched anyhow.  :lmao: 
The previous description don't count cause I believe she was married up north and then moved down south where the new marriage laws now take effect.


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## Derrel (Mar 11, 2014)

runnah said:


> Derrel I have had great success using the mark 3 and 600 ex rt in ETTL mode. In all camera mode it evaluates the scene and delivers great results.



Just wondering if the flash exposure compensation or FEC is "tied to" the exact AF point in use like it was before. Last time I really read up on the issue of E-TTL was well before the 5D-III was out, and a group of wedding photographers were discussing how sensitive the flash metering was with regard to active AF point. It's been a long time ago. I know that Nikon had  a heck of a time developing it's D-TTL protocol with the first d-slr's; it was very erratic at times. Then they came out with i-TTL. Canon had pretty much the same issues; e-TTL had issues, e-TTL-II is supposed to be better (it seemed okay to me).

I'm just sort of thinking the "newest" technology, the iFCL metering might be the last, final,critical piece for really good automatic flash control in run-n-gun type use.

Canon Professional Network - iFCL metering


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## robbins.photo (Mar 12, 2014)

gryphonslair99 said:


> robbins.photo said:
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Well honestly I think that might be a little short sighted.  I mean think about the possibilities here.  "Honey, I'm watching the game right now.  Don't you have another husband you can discuss your 'feelings' with?" - Lol


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## runnah (Mar 12, 2014)

Derrel said:


> runnah said:
> 
> 
> > Derrel I have had great success using the mark 3 and 600 ex rt in ETTL mode. In all camera mode it evaluates the scene and delivers great results.
> ...




I have no idea. I use single point AF 99% of the time and with ettl i haven't had a blown out wonky photo. The wedding I shot I used that combo the entire time and never had any issues.


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## Big Mike (Mar 12, 2014)

e.rose said:


> Big Mike said:
> 
> 
> > In a nutshell...
> ...



Yes, that is one of the inherent problems with using flash, whether manual or TTL.  People/objects at different distances are hard to light evenly.  

What we need to keep in mind, is a property of lighting (specifically, a property of diffuse reflection) called the Inverse Square Law.  It states that the amount of light being reflected (the brightness) of something, is inversely proportional to the distance it is from the light source.  
Basically, if you are shooting your flash straight ahead and you have two people in frame, one at 5 feet and one at 10 feet....the person at 10 feet will up roughly 4 times darker.  (5:10 is a factor of two, two squared is four). 
If the close person moves to only two feet away, and the other person is still 10 feet away, now you have a factor of 5, and the further person will be 25 times darker (or you could say that the close person would be 25 times brighter).  

So what I'm trying to say is that the distance, from light source to subject(s), is very important....but what we really need to pay attention to, is when the distance to multiple subjects is different by a larger factor.  

If you're shooting two people who are two feet (further from you) away from each other.....if they are 14 feet and 16 feet away, they would be lit relatively evenly...but if they were 4 feet and 6 feet, they would be rather unevenly lit.

Do you get where I'm going here?

So the key to avoiding super bright or super dark people/objects, is trying to even out the distances (from the light source).  Shooting straight ahead, this can be tough.  But this is one of the reasons why bouncing the flash works so well.  If you bounce the flash off of a wall that is 10 feet away, then the path of light might be 24 feet to the first person and 25 feet to the second person, the difference is negligible.  

So not only does bouncing give you a softer light (the spot of light on the wall is much larger than the flash, thus you get softer light), and not only is it directional (it doesn't come from the direction of the camera), but bouncing off of walls/ceilings allows you to even out the distances to multiple subjects which evens out the lighting.

Of course, not every location allows for good bouncing, but with a powerful flash and helpful settings (larger aperture and higher ISO) you'd be surprised how well it can still work, even when the bounce surfaces are dark and/or far away.


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## e.rose (Mar 12, 2014)

gryphonslair99 said:


> robbins.photo said:
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All of this is accurate.

And hilarious. :lmao:


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## e.rose (Mar 12, 2014)

Big Mike said:


> e.rose said:
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Yes that definitely makes sense, and I do already bounce my flash, but the issue isn't that I'm trying to shoot 2 different people at two different distances at the same time...

It's that the people I AM shooting are further away, and there happens to be this random dude on the dance floor (who I'm not focusing on and trying to ignore/avoid) who happens to be closer to me and in frame at the edge of the frame that seems to be throwing my exposure off, because *he's* well lit, but the people I'm focusing on are not...

Does that make sense?

So I guess I'm trying to figure out what the camera/flash is seeing when shooting on camera ETTL so that I can trick it into lighting the further people correctly, when I'm focusing on them, vs. people who are closer to me (when I'm actually focusing on the people closer to me).


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## pgriz (Mar 13, 2014)

Emily, as Mike has already said, you're working against the inverse-square law in terms of light fall-off.  If both people are the same distance from the (single) flash, then you'll have the right amount of light.  If they are at different distances, then it's gonna be hard to get an even exposure for both.  The method I've used in situations where people were at different distances from the "main" flash, is to set up additional "slave" flashes that would provide more-or-less even light in the "interior" area delimited by the four perimeter flashes.  This can work if you're in a rectangular room with 9-12 ft. high ceilings.  If you put the flashes at the corners, illuminating the ceiling, they will give a more-or-less even light throughout the enclosed space.  Of course, if you do this, you need to be sure that your camera angle doesn't catch the illuminated ceiling as part of the image.  This approach has worked for me in shooting family events where everything was happening in the same room.  

If you're shooting in a reception hall, then this approach will probably not work, as the amount of light needed to light up the area evenly becomes more than what speedlights can provide.  

As for the scenario where a foreground person is throwing off your flash exposure, I know that my camera's ETTL processing looks at the entire frame, and will not get the right exposure for the back person.  However, maybe Runnah's experience with his 5DIII shows that the newer cameras have more intelligent handling of the exposure calculation.


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## Big Mike (Mar 13, 2014)

e.rose said:


> Big Mike said:
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> > e.rose said:
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A couple things come to mind.

Firstly, try to avoid having someone get in between your flash (bounce path) and your subject.  Easier said than done, I know.  Maybe using a longer focal length, would help prevent people from sneaking into the edges of your shot.

Another option might be to use FEL, Flash Exposure Lock.  With FEL, you tell the camera to fire the preflash and then wait until you open the shutter, before it fires for real.  So you could use FEC to lock in the (hopefully) correct flash power for your subjects, then wait until just the right moment to snap the shot.


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## e.rose (Mar 13, 2014)

pgriz said:


> Emily, as Mike has already said, you're working against the inverse-square law in terms of light fall-off.  If both people are the same distance from the (single) flash, then you'll have the right amount of light.  If they are at different distances, then it's gonna be hard to get an even exposure for both.


 
Right. I get that. But I'm not *trying* to evenly lit both people. I only want to light up the people in the back, and if the drunk dancing dude, frame right, is totally blown out... no biggie, because I'm probably going to try and crop him out anyway. Haha.



pgriz said:


> The method I've used in situations where people were at different distances from the "main" flash, is to set up additional "slave" flashes that would provide more-or-less even light in the "interior" area delimited by the four perimeter flashes.  This can work if you're in a rectangular room with 9-12 ft. high ceilings.  If you put the flashes at the corners, illuminating the ceiling, they will give a more-or-less even light throughout the enclosed space.  Of course, if you do this, you need to be sure that your camera angle doesn't catch the illuminated ceiling as part of the image.  This approach has worked for me in shooting family events where everything was happening in the same room.



That sounds great, however, I don't shoot weddings on my own. I hate weddings. 

I'm a second shooter for other people, so I'm working with what they have set up.

If they have the floor evenly lit with studio strobes about the room... they're tied to them. I'm not. So I'm still having to use on camera flash.

And if they DON'T have the floor evenly lit... I'm still having to use on camera flash. 

Which is why I want to better understand the way on camera flash see things so that I can be a better *SECOND* shooter... haha. 



pgriz said:


> As for the scenario where a foreground person is throwing off your flash exposure, I know that my camera's ETTL processing looks at the entire frame, and will not get the right exposure for the back person.  However, maybe Runnah's experience with his 5DIII shows that the newer cameras have more intelligent handling of the exposure calculation.



I think I need to bust out my manuals again to see what they say about that.



Big Mike said:


> A couple things come to mind.
> 
> Firstly, try to avoid having someone get in between your flash (bounce path) and your subject.  Easier said than done, I know.  Maybe using a longer focal length, would help prevent people from sneaking into the edges of your shot.
> 
> Another option might be to use FEL, Flash Exposure Lock.  With FEL, you tell the camera to fire the preflash and then wait until you open the shutter, before it fires for real.  So you could use FEC to lock in the (hopefully) correct flash power for your subjects, then wait until just the right moment to snap the shot.



Problem with using a longer focal length (at least at the wedding I was just at) was that the dance floor is PACKED... and I have a 28... a 50... and a 70-200.  The 50mm is too long for most everything I was trying to capture that night, let alone the 70-200.

The 50mm would have come in handy FABULOUSLY in the situations I'm talking about... but it's a prime... and my 28 is a prime... and I can't switch back and forth while I'm on the floor and all that action is happening.

So if I see something happening a little further away I shoot, and crop.

Not ideal, but until I sell my 50 and 28 and trade it in for a 24-70 (HAR. HAR. HAR. That's really funny because I don't have enough money to pay the balance of that even after I sell the first two lenses...), that's kind of how it has to work.


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