What will E-TTL adjust?

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Simmotino

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Maybe a stupid question (but as I've spent far too many attempts trying to get my head around flash without success I don't really mind!) but, if you are shooting in AV mode, the camera will adjust shutter speed (and ISO if set that way) to expose correctly for the aperture being used.

If you introduce a speedlite set to E-TTL to that equation, what will change?

Will it still use the same shutter speed but keep the ISO lower due to the extra light fed from the speedlight, or will the ISO stay the same and the shutter speed increase, or a bit of both?

:shrug:
 
My take on this would be that the aperture stays as set, the shutter speed is then adjusted to either a standard flash sync speed (1/125 perhaps) or another speed if you have set the custom function to match curtain sync, Iso remains as set and the metering system adjusts the light output from the speedlite to match an accurately exposed picture using various parts of the scene with a bias towards accuracy at the focus point.

Matt
 
I don't know about other Canon models but on my 50D with the camera set on AV the camera meters for the background and uses the flash for fill in. To use flash for the whole exposure I set the aperture, shutter speed and ISO that I want in manual and the ETTL metering sets the flash power to provide a correct exposure.
 
So by fixing the aperture (in AV mode) it's not necessarily going to produce a well exposed shot as a whole if, for example, you're shooting people in a room.

You'll get well exposed people, but might not get anything of the room itself.

Accordingly, better to shoot manual, set the aperture AND shutter, and leave the flash to do the rest? :shrug:
 
The standard Canon default on Av (which you can change in custom functions) is for the aperture to be set and the shutter speed will be adjusted by the camera to match the ambient light, down to 30secs if needs be.

Then when you fire the gun in E-TTL, it will match the flash exposure to the f/number and ambient level for an overall balanced exposure.

To change the brightness of the background, adjust the compensation dial on the camera (alters the shutter speed). To change the brightness of the flash, adjust the compensation on the gun (alters the flash power) - you can also do it within the camera menu on some flash guns.

You can also lock any of these settings if you like, use the FEL* button if that suits.

Basically, you can do anything once you get the hang of it. Any number of modes, options, settings, flash configurations etc etc :thumbs: I don't find it very intuitive and you sometimes get confused, but it works - stick with it.

A more digestable version of that link above, by the same chap, is to be found in this very good new book http://www.amazon.co.uk/Mastering-C...244X/ref=sr_1_1?ie=UTF8&qid=1295739677&sr=1-1
 
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HoppyUK said:
The standard Canon default on Av (which you can change in custom functions) is for the aperture to be set and the shutter speed will be adjusted by the camera to match the ambient light, down to 30secs if needs be.
Click to expand...

That's in Tv (and M) mode. Av & P should range between max shutter sync and 1/60th.
 
DemiLion said:
That's in Tv (and M) mode. Av & P should range between max shutter sync and 1/60th.
Click to expand...

No, the default for Av is up to 30secs. In Av custom functions, 5DII has either 1/60sec or 1/200sec options.
 
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DemiLion said:
That's in Tv (and M) mode. Av & P should range between max shutter sync and 1/60th.
Click to expand...

Not on most Canon bodies. In AV mode the camera sets the shutter speed most suitable for the metering, then uses the flash to "fill" the subject, up to 1/125 or 1/250, depending on your body.

Steve

Sent from my iPad using TP Forums
 
Jelster said:
Not on most Canon bodies. In AV mode the camera sets the shutter speed most suitable for the metering, then uses the flash to "fill" the subject, up to 1/125 or 1/250, depending on your body.

Steve

Sent from my iPad using TP Forums
Click to expand...

Tes you set the aperture the camera will change the SS to maintain a good exposure (or what it thinks is a good exposure). SS will go not go above the sync speed but if you are in bright sunlight 1/200th or whatever your sync speed is, may end up grossly over exposing your images so care needs to be taken that you either switch to high speed sync (and accept the loss of range/power) or change to a narrower aperture to keep the SS at or below sync speed.

Using M with ETTL is much easier. If you can dial in a little under exposure to the scene the subject seems to pop.
 
Manual shooting with a flash attached in auto mode is a piece of cake. If your flash has a long enough range it's easier than shooting in Tv or Av mode because you can set the aperture and shutter speed that you want and let the flash take care of the exposure. There's no dilemma about keeping the aperture wide enough to ensure the shutter is fast enough to freeze action.

For example, if I'm shooting macro I set the aperture to f/18 -f/22. in Av mode this would lead to a very slow shutter speed and plenty of movement blur. In manual mode I also set the shutter to 1/125 and the flash provides enough light for a correct exposure.
 
Presumably then, in manual, changing the aperture is ONLY going to change the DoF so you'd need to change the shutter speed to adjust the ambient exposure?
 
Sort of, depending on what you want to achieve. Shutter speed + ISO for ambient , Aperture for DoF and FEC for flash control or alternatively move into manual flash and adjust accordingly (I've yet to brave that one!). Although obviously aperture will have an affect on the ambient lighting relation to SS and ISO.
 
Right (think I *might* actually be getting this finally!) so, M mode on camera, flash on E-TTL, and then:

Aperture for (primarily) DoF adjustment
Shutter speed for ambient
ISO for ambient (and noise control presumably?)
FEC on camera for strength of fill(?)

Sound about right? :shrug:
 
:D

I'd say so, but don't quote me on it.

There'll be loads of opportunities to practice fill lighting at Borough Market in a couple of weeks. Maybe we should set that as a specific learning target?
 
Aperture affects flash power. Just means the smaller the aperture the more juice your flash needs to pump out therefore slower recycling and shorter battery duration. Higher ISO can help reduce the flash power if you need to.
 
Having experimented my way through a set of AA's this afternoon I do believe I've actually, finally, managed to grasp the basic concept.

Who'd have thought M would make it so easy?!

Thanks for all your input, I'm off for a lie down now! :nuts:
 
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