E-TTL preflash

[wintoid]

I'm still trying to get to grips with my 550ex and 300d. I've read all the commonly posted links to information about flash, and searched this forum to see if there's an answer to my question, but I couldn't find it, so here goes...

As I understand it, E-TTL will fire a preflash in order to work out how powerfully to fire the flash. I've never been able to see this preflash. How can I tell that the preflash has fired? I'm wondering if it's just so fast that it's not possible to notice it.

[scottbergerphoto]

I'm still trying to get to grips with my 550ex and 300d. I've read all the commonly posted links to information about flash, and searched this forum to see if there's an answer to my question, but I couldn't find it, so here goes...

As I understand it, E-TTL will fire a preflash in order to work out how powerfully to fire the flash. I've never been able to see this preflash. How can I tell that the preflash has fired? I'm wondering if it's just so fast that it's not possible to notice it.
The preflash fires as you fully depress the shutter button, but before the shutter opens, so it can be read by the camera meter. Then the shutter opens and the flash fires. You can prove this to yourself by using FEL- Flash Exposure Lock. Each time you depress FEL a preflash fires. The only other way is to put the camera into Second Curtain Sync with a long exposure, if the 300D has Second Curtain Sync. That causes the flash to fire at the end of the exposure instead of the beginning, so you would see two pops.
Regards,
Scott

[Jesper]

If you put your camera or flash on 2nd curtain sync (I don't know if that's possible with the 300D - with the 10D, it's a custom function, but the 300D doesn't have custom functions - I don't know if you can set it on the 550EX) the pre-flash will fire when you press the shutter button, and the "real" flash will fire just before the shutter closes again. So if you set a slower shutter speed, you'll easily be able to see both flashes.

[wintoid]

Thanks guys. So you're saying it probably is happening, it's just too fast to see?

I guess I expected it to be like the double flash of red-eye reduction.

[PacAce]

Thanks guys. So you're saying it probably is happening, it's just too fast to see?

I guess I expected it to be like the double flash of red-eye reduction.

I can see the prefalsh with my 10D. I'm not sure why the 300D would be any different. Try shooting yourself in the mirror to make sure. But if you're getting good or acceptable flash pictures, I wouldn't worry about it that much if you don't notice the preflash going off.

[wintoid]

Ah yes, well that's where it all started :( Some of my flash pictures are fine, but many of them are not, and that's what got me worrying about E-TTL in the first place.

As I understand it, if (for example) you set the camera to manual, set the aperture to f3.5 and the shutter to 1/200, the flash should adjust its power through the magic of E-TTL to perfectly expose the subject in the centre area of the frame (being centre weighted), but the background/edges will be exposed as per the aperture/shutter speed... in other words dark in most cases. However, I am frequently finding that my foreground is underexposed, especially when using bounce. Incidentally, even though the 550ex manual says the flash will switch to 50mm when in the bounce position, my 550ex says "--" where the zoom distance would be shown when I put it in the bounce position.

It does seem like an awful lot of people have problems getting good exposures with the 300d/550ex combination. To be honest, I was doing much better with my Sigma DG500 ST, which I ebayed to buy the 550ex :(

[Cordell]

Just to be sure, is the flash set to ETTL and no other compensations in camera or flash?

[nosquare2003]

Ah yes, well that's where it all started :( Some of my flash pictures are fine, but many of them are not, and that's what got me worrying about E-TTL in the first place.

As I understand it, if (for example) you set the camera to manual, set the aperture to f3.5 and the shutter to 1/200, the flash should adjust its power through the magic of E-TTL to perfectly expose the subject in the centre area of the frame (being centre weighted), but the background/edges will be exposed as per the aperture/shutter speed... in other words dark in most cases. However, I am frequently finding that my foreground is underexposed, especially when using bounce. Incidentally, even though the 550ex manual says the flash will switch to 50mm when in the bounce position, my 550ex says "--" where the zoom distance would be shown when I put it in the bounce position.

It does seem like an awful lot of people have problems getting good exposures with the 300d/550ex combination. To be honest, I was doing much better with my Sigma DG500 ST, which I ebayed to buy the 550ex :(

1. Using manual mode (aperture/shutter speed) will not make the flash to use centre weighted metering. The metering of flash is focus sensitive and it will be biased against the selected focus.

2. You are right that the background / foreground exposure is controlled by the aperture / shutter speed. If you need a "proper" background / foreground exposure, a tripod for longer exposure is required.

3. The 550EX has a zoom head. But when a bounce flash is used, there's no need to zoom.

[wintoid]

It's definitely using E-TTL, and whilst I do gradually add in compensation on the 550ex (the 300d doesn't have compensation!) to get the right histogram, I always start from a non-compensated setting.

All the shots I've taken in Manual mode indicate "centre weighted metering" in the EXIF information. Nosquare, have I misunderstood? Does that actually mean the metering within the camera, and not the flash? I suppose because I'm making manual adjustments, I'd assumed that must mean the flash, but I guess on reflection it probably means the exposure indicator in manual mode. Hmmmmm. Even so, that indicator is usually showing "underexposed" for obvious reasons.

I'm shooting in manual mode because I want to control the shutter speed AND have control over DOF, so I avoid Tv and Av modes with flash anyway. I'm prepared to sacrifice losing complete control over the brightness of my backgrounds, so long as the foreground is exposed correctly!

re the zoom head... is that related more to the width of light than anything?

Thanks for your responses. I think some subtle points are gradually slipping into place (although I still don't understand why my shots are often badly exposed)

[scottbergerphoto]

All the shots I've taken in Manual mode indicate "centre weighted metering" in the EXIF information. Nosquare, have I misunderstood? Does that actually mean the metering within the camera, and not the flash? I suppose because I'm making manual adjustments, I'd assumed that must mean the flash, but I guess on reflection it probably means the exposure indicator in manual mode. Hmmmmm. Even so, that indicator is usually showing "underexposed" for obvious reasons.

The Center Weighted Metering applies only to the ambient metering. The flash metering in AF is weighted towards the selected autofocus points. If you switch to Manual Focus the flash metering is spread out to average all the focus points. So if your picture has large differences in tone, you might want to switch to Manual Focus when using flash.

If as you say, you want to nail the foreground, and don't care about the background, in Manual Mode set the shutter speed to 1/200 and use the Aperture to control DOF or set the camera to Av with shutter speed locked at 1/200 (Cfn 3). That will reduce any blur from subject/camera movement. You will the have two superimposed pictures: one of the ambient light at 1/200 and the f stop you chose, and one at 1/10,000(flash duration) and the f stop you chose. Both of these exposures occur at the same time. In dim light the first exposure will contribute very little due to the 1/200 shutter speed. So you are left with only the exposure of the foreground by the flash.
Regards,
Scott

[wintoid]

Scott,

Thank you so much for that explanation. This is so counter-intuitive, that I'm not surprised the information didn't sink in.

As a relative newbie, I'm nervous to express my discontent, as I don't feel I have a solid enough foundation to justify it, but good grief who designed this thing!

The practical upshot of this is:

1) When focusing on a dark object, the flash will fire strongly, with a good chance of overexposure, and blowing out the highlights of the frame
2) When focusing on a light object, the flash will fire weakly, with a good chance of underexposure and losing shadow detail in the darker parts of the frame
3) When focusing on something midtoned, exposure should be good across the whole image

OK fair enough, the 3 points listed above do apply when shooting without flash, but not to such extreme degrees I would imagine.

I thought the whole point of switching to centre weighted averaging with E-TTL was so that the flash power was controlled to give a good exposure over the whole frame! There *really* ought to be some way to change this behaviour. As things stand, there is NO WAY you can expose a frame correctly with just E-TTL if it contains light and dark objects at different focus distances....

Is this behaviour the same in P mode?

I suppose now that I know this, I can dial in some compensation in the 550ex depending on the tone of the object I am focusing on. I wonder if that will be enough to get me the shots I want.

Thanks again!!

[slin100]

You've stumbled onto one of the greatest criticisms of ETTL, that it is too heavily focus-point centric. Another way to get center-weighted averaging is to enable CF 4 to remap focusing to the * button. You, then, focus with the button, release the button and fire the shutter. It's important to release the * button. Otherwise, flash exposure will revert to using the focus points.

Although it's no help to us owners of existing models, Canon is releasing ETTL-II with their 1D Mk II and the Elan 7n/7ne film cameras. ETTL-II has a mode for center-weighted averaging without the need to enable CF 4 or to switch to manual focus.

[scottbergerphoto]

Switch to Manual Focus. It will cause the flash to use all the focus points in calculating flash output.
Scott

[wintoid]

I don't think the 300d has custom functions, otherwise I would surely use that.

I guess I'm going to try to get used to dialing in some compensation on the flash. It might be ok. If that doesn't work, I'll give serious thought to manual focus.

The 2 lenses I have are FTM I think (50mm 1.4 and 24-85). Does that mean I can just touch the focus ring slightly, and my exposure will be averaged over all focus points, or doesn't that count as a "proper" manual focus? I don't really want to turn the switch from AF to MF if I can avoid it.

Wow, I sound really miserable. I'm a cheerful chappy really, honest!! :roll:

[scottbergerphoto]

Sorry, but you really do have to flip the switch on the lens from AF to MF.
Scott

[wintoid]

Flash compensation or bust then! Thanks for confirming that Scott.

[dpanicc1]

2. You are right that the background / foreground exposure is controlled by the aperture / shutter speed. If you need a "proper" background / foreground exposure, a tripod for longer exposure is required.

And, better make sure your subject holds still while you expose for ambient.