Flash exposure

[Leandro Bento]

Hey everybody,

How do you guys get consistent results using flash? I have been in situations where I am standing right in front of my subjects, and I get different results taking 2 photographs one after the other (all in the same room). I have a 550 and a quantum flash and power pack. I also shoot in P mode. So there are instances when one photo at 1/60 , f/4 is underexposed, while the following photograph hs a better exposure at 1/60, f/5.6. :( It's weird, the f/4 photograph is under, while the f/5.6, which is a smaller aperture, is well exposed. That's using the 550. With the Quantum I get the opposite results: overexposed shots. Am I doing something wrong? Do you guys have any advice you could give me?
Any help is appreciated.

Leo

[jamiewexler]

What body are you using?

[Wilt]

I assume your 550 is with flash control on ETTL, and with the Quantum it is on Auto?

If so, that explains it...Canon ETTL is not consistent and it often underexposes, so that FEC = +2/3 or +1 EV is dialed into the camera all the time for situations where flash is the main source of light.

As jamie asks, which body are you using this with?

[ssim]

Which quantum flash are you using. I just got the Quantum (http://www.qtm.com/QFlash/?res_set=yes&res=1280&resh=1024)T5D with the DW13 QTTL adapter. I haven't had any trouble with it. Exposures are very consistent.

With the 550/580 I always set the camera in manual and then let the flash compute the amount of power output. I found the exposure in AV/TV inconsistent as well and I never did shoot in P mode. Shooting in manual my exposures are fairly consistent. I would give this a try and see if your results improve.

[Leandro Bento]

I used the 20D.
The Quantum flash is the T5D. I don't remember the adapter name right now but I guess the one for the 20D. And how exactly do you meter for your exposures in manual? Do you use a handheld meter? if so, incident reading or reflected? Do you use a gray card?

Thanks,
Leo

[Wilt]

I used the 20D.
The Quantum flash is the T5D. I don't remember the adapter name right now but I guess the one for the 20D. And how exactly do you meter for your exposures in manual? Do you use a handheld meter? if so, incident reading or reflected? Do you use a gray card?

Thanks,
Leo

Yep 550 on ETTL with 20D will likely give you underexposure unless you dial in FEC. I don't know the Quantum enough to know if that adapter supports ETTL, or if it merely provides viewfinder indicators and triggering while the flash is on Auto.
Flash metering usually done with incident meter, but sometimes reflected light measurement is used (for example, with tranmitted light thru colored gel thru the backdrop)

[Leandro Bento]

I did increase the flash output, but still got underexposed pics. As I said before, I am getting underexposed photos with a wide aperture and good exposures with a slightly narrower aperture. It just doesnt make sense to me.
Thank you all for your replies.

Leo

[bogleric]

I assume your 550 is with flash control on ETTL, and with the Quantum it is on Auto?

If so, that explains it...Canon ETTL is not consistent and it often underexposes, so that FEC = +2/3 or +1 EV is dialed into the camera all the time for situations where flash is the main source of light.

As jamie asks, which body are you using this with?

How much of a different does it make if you set the FEC on the camera or the flash unit itself?

[Wilt]

How much of a different does it make if you set the FEC on the camera or the flash unit itself?

I don't know...I alway have dialed it into the body.

[bogleric]

I don't know...I alway have dialed it into the body.

I will have to play with this, as I have always dialed it into the flash unit. Intuitively I wouldn't think there would be much difference.

[Wilt]

I did increase the flash output, but still got underexposed pics. As I said before, I am getting underexposed photos with a wide aperture and good exposures with a slightly narrower aperture. It just doesnt make sense to me.
Thank you all for your replies.

Leo

Yeah, that doesn't make sense to me either. I can't even begin to think of a reason it might act in that manner! Well one...if your camera was on P, and the large lens aperture caused it to do ambient light exposure with flash fill, you might interpret the result as underexposed. But if you're using smaller lens aperture, the camera logic then thinks it needs to do flash exposure with flash as the main light..

Can you post example?

[tim]

Practice and experience. (answering the original question)

[ssim]

I used the 20D.
The Quantum flash is the T5D. I don't remember the adapter name right now but I guess the one for the 20D. And how exactly do you meter for your exposures in manual? Do you use a handheld meter? if so, incident reading or reflected? Do you use a gray card?

Thanks,
Leo

I'm using the Quantum and the 580's on either a 1DMKII or 5D. I don't do much flash work with the 20D/30D.

When you put your camera in manual and set your falsh to ettl the flash reads what your shutter and f-stop is an adjusts the amount of output light accordingly. Now if you are consistently getting underexposed images based on a constant setting then you could dial in a + amount of output on the flash. I have not had the problems you are encountering but this could be because of my desire to work in manual mode on the camera. Give this a serious try and see if you like it.