Back Button focus and E-TTL

Ok, so I admit right from the beginning that I am a flash n00b.

I went through the "I shoot in natural light because I can't use flash" stage and then the "I want to learn" stage before getting to "Damnit, I AM going to get this or the world will burn" stage where I am now.

That means I don't know sh...er... a lot.

I have not had any real experience with, and less understanding of, E-TTL but want to change that.

I was having issue with lackluster performance when experimenting using E-TTL, and was surfing around trying to find out why.

It turns out that if you are like me and have switched to back button focusing, you sometimes focus and take your thumb off the button before shooting. Did you know that you are causing the E-TTL system to go into evaluative mode instead of metering at the focus point?

Well... now you do. I thought I would share in case there are others like me who are trying to learn.

This page explains it very nicely: http://www.dlcphotogra​phy.net/ETTL/ETTL.htm

You are talking about the back focus button and the article is talking about the the AEL button. You probably mean the same thing or you may have programmed the AEL button to be used as back focus button when the flash is off the camera.

When I press the AEL button then flash fires and the system calculates the flash exposure only within the spot meter circle. This is the only way to obtain spot metering with flash. The back focus button is usually a different button.

digital paradise wrote in post #16807430
You are talking about the back focus button and the article is talking about the the AEL button. You probably mean the same thing or you may have programmed the AEL button to be used as back focus button when the flash is off the camera.

When I press the AEL button then flash fires and the system calculates the flash exposure only within the spot meter circle. This is the only way to obtain spot metering with flash. The back focus button is usually a different button.

On my t5i, the back button for focus is the AE button. AE is shifted to the half-push on the shutter button.

I experimented after reading that, and I can duplicate his results, though I didn't test as rigorously as he did..

The smaller camera models don't have buttons for everything. The biggest ones allow you to split up the functions on different buttons.
For example, a 7D or more advanced camera has enough buttons to do all this at the same time:
AF-ON: Focusing and metering for ambient light.
*: Metering and locking exposure for ambient light.
FEL: Spot metering of flash and locking flash exposure.
Half-press: Metering for ambient only.

On cameras lacking AF-ON and/or FEL, these functions have to be either abandoned or combined with some other function.

Sorry I meant the FEL not the AEL. So you are you using the rear button to both focus and the use the FEL?

digital paradise wrote in post #16807558
Sorry I meant the FEL not the AEL. So you are you using the rear button to both focus and the use the FEL?

Evidently, on the t5i, the FEL and AEL are the same button, but flash exposure lock only works with onboard flash deployed, or so the manual says anyway. There is nothing in the manual about FEL with a flash unit either on or off the camera.

I know that the manual is not all-encompassing, so that may be just an omission.

In any case, with the buttons switched (AE & Focus), it would make sense that the shutter button would perform the FEL function assuming it works with a flash unit.

Ok.. so if that is all correct, when I focus with the AE button, and half-depress the shutter button to get the exposure reading, it should be locking the flash exposure at the same time, right?

But it's not. What I get in E-TTL mode with external flash attached to the hotshoe is this:

If I hold the focus, depress the shutter half way and then take the shot, I get fill flash.
If I focus and release, depress the shutter halfway and then take the shot, I get sometimes flash, sometimes not, sometimes lower level flash. (Mostly no flash)

So I have to conclude that FEL is not available except with onboard flash, right?

It appears, by the behavior of the flash when I don't have an active focus point, that it is evaluating the entire scene instead of spot evaluating like it does when I DO have an active focus point.

I am the first to admit that I am so squeaky new to this that I don't know what I don't know, but doesn't that sound like the article?

If I am missing something, please tell me! I want to learn.

I just looked at this, and your Flash Exposure Lock is bound to the Auto Exposure Lock. Depressing the shutter halfway doesn't lock the spot flash metering like Flash Exposure Lock does, nor the ambient exposure metering like the Auto Exposure Lock. Your camera meters the flash at the moment the shutter is depressed in either evaluative flash metering or average flash metering, depending on what you have it set to.

Evaluative or average metering solely for the flash is a unique distinction between modes that a lot of people aren't aware of. They are distinct from the ambient metering selection you have made (spot, evaluative, partial, average.) Which do you have your flash set to?

Vetteography wrote in post #16807402
Ok, so I admit right from the beginning that I am a flash n00b.

I went through the "I shoot in natural light because I can't use flash" stage and then the "I want to learn" stage before getting to "Damnit, I AM going to get this or the world will burn" stage where I am now.

That means I don't know sh...er... a lot.

I have not had any real experience with, and less understanding of, E-TTL but want to change that.

I was having issue with lackluster performance when experimenting using E-TTL, and was surfing around trying to find out why.

It turns out that if you are like me and have switched to back button focusing, you sometimes focus and take your thumb off the button before shooting. Did you know that you are causing the E-TTL system to go into evaluative mode instead of metering at the focus point?

Well... now you do. I thought I would share in case there are others like me who are trying to learn.

This page explains it very nicely: http://www.dlcphotogra​phy.net/ETTL/ETTL.htm

Now here's my question, how is this having a detrimental effect on your use of flash?

Adharr wrote in post #16807770
I just looked at this, and your Flash Exposure Lock is bound to the Auto Exposure Lock. Depressing the shutter halfway doesn't lock the spot flash metering like Flash Exposure Lock does, nor the ambient exposure metering like the Auto Exposure Lock. Your camera meters the flash at the moment the shutter is depressed in either evaluative flash metering or average flash metering, depending on what you have it set to.

Evaluative or average metering solely for the flash is a unique distinction between modes that a lot of people aren't aware of. They are distinct from the ambient metering selection you have made (spot, evaluative, partial, average.) Which do you have your flash set to?

Ok, bear with me here because I am a little confused.

On this camera, AEL and FEL are combined in a single button, the AE button.

I have back button focusing turned on, and that switches the AE function to the shutter button and uses the AE button for focusing.

Are you saying that the FEL function is STILL locked to the AE button even if the exposure function has been switched? That might make sense as well considering my issue, but would be a really odd way to do things, especially since you would not be able to lock the flash exposure and the focus independently.

It seems like it would make more sense, and would be easier, to move the FEL along with AEL to the new button.

According to that article (and I know it may be incorrect, but the evidence he posted makes sense) the camera is metering for flash in E-TTL mode based in spot mode if there is an active point focus point, and in evaluative mode if there is not, independent on your AE exposure mode set in the menu.

Is this wrong?

Scatterbrained wrote in post #16807785
Now here's my question, how is this having a detrimental effect on your use of flash?

Read on, MacDuff!

Ok, being serious here. When shooting a shadowed object against a bright backdrop;

If I hold the focus button, I get reliable, good level flash.

If I focus and release the focus lock, then take the pic, I get unreliable flash. I have had insufficient flash if I am pointing right towards a light source, or no flash at all if the light differential is not that wide.

And this is with all three flash units I own, not just one (I checked in case there was an issue)

This behavior, and because I didn't understand what E-TTL really was, caused me to do a web search to learn more about E-TTL. I saw a post asking about almost the same issue I was having and it lead me to the article in the OP.

I'm busy tonight but first thing tomorrow I'd be happy to explain how ETTL works when using a flash. I think that will help you with flash exposures.

Vetteography wrote in post #16807812
Read on, MacDuff!

Ok, being serious here. When shooting a shadowed object against a bright backdrop;

If I hold the focus button, I get reliable, good level flash.

If I focus and release the focus lock, then take the pic, I get unreliable flash. I have had insufficient flash if I am pointing right towards a light source, or no flash at all if the light differential is not that wide.

And this is with all three flash units I own, not just one (I checked in case there was an issue)

This behavior, and because I didn't understand what E-TTL really was, caused me to do a web search to learn more about E-TTL. I saw a post asking about almost the same issue I was having and it lead me to the article in the OP.

Shoot in manual mode. Set the exposure to underexpose the background, let the bounced flash handle the subject.

IMAGE LINK: https://flic.kr/p/dEpk​Zt

Scatterbrained wrote in post #16808149
Shoot in manual mode. Set the exposure to underexpose the background, let the bounced flash handle the subject.

IMAGE LINK: https://flic.kr/p/dEpk​Zt

I have been practicing with doing exactly that when I got sidetracked into this E-TTL snipe hunt by a shootout video I saw (Manual vs TTL) and thought I should at least know what TTL was all about. You are right in that it definitely works and, if this thread is any indication, it is probably easier as well!

I leave the flash in E-TTL but use the camera in Manual. This way I control the camera exposure (background) and leave the subject up to the flash. Works pretty well more often than not.

Vetteography wrote in post #16807798
Ok, bear with me here because I am a little confused.

On this camera, AEL and FEL are combined in a single button, the AE button.

I have back button focusing turned on, and that switches the AE function to the shutter button and uses the AE button for focusing.

Are you saying that the FEL function is STILL locked to the AE button even if the exposure function has been switched? That might make sense as well considering my issue, but would be a really odd way to do things, especially since you would not be able to lock the flash exposure and the focus independently.

It seems like it would make more sense, and would be easier, to move the FEL along with AEL to the new button.

According to that article (and I know it may be incorrect, but the evidence he posted makes sense) the camera is metering for flash in E-TTL mode based in spot mode if there is an active point focus point, and in evaluative mode if there is not, independent on your AE exposure mode set in the menu.

Is this wrong?

I'm going to read your camera manual to verify something and be right back.