Flash Exposure Compensation Question on the 20D

[SHKJ]

Hi All,

I was justwondering, with my 20D I generally attach my 430EX flash and tilt the head either 45 or 60 degreesto bounce the flash off the ceiling and shoot in manual mode between 1/60th & 1/125th at F4.0-F5.6 with a Stofen Onmi-bounce at ISO400 with just ok results..but most of the time the pictures are overexposed

I also add +2/3 Flash exposure Compensation set in the camera..this works great with the on-board flash

My question is being that I am shooting in Manual modewith an external flash is the camera really applying the +2/3 FEC and is that why my pictures are over exposed ??

basically what is the best way handle flash with the 20D ??

Thanks in advance...Shkj

[mbze430]

in Manual mode, you set your flash to expose for your subject.

The simplest way to look at this is. Shutter/Aperture controls background/ambient light, and FEC and Aperture controls subject exposure.

Of course Aperture also controls your DOF.

And of course Shutter will control your motion.

I cover a range of events.. From hollywood A list to Fashion Runway. So flash is a big part of my life. Depending on the situation I might be using a portable softbox or a LS2. But I first make sure I know how fast things are moving (nothing than a super blurry picture). That will give me an idea what shutter speed to keep from going over or under. Next I check out how much background I have. This will tell me how much ISO I need + shutter speed. How far am I from subject, than subject to background, this gives me an idea of aperture. From there Its pretty much basic photography. I never close up aperture more than f5.6, this keep the background still pretty blurry and not imprint any distraction to the picture.

Of course I carry a 2 battery packs, so I get the 1s recharge time, to keep shooting. You'll never know which star will show their personal parts next

[Jon]

You're bouncing off the ceiling and using an OmniBounce? ISTR other threads here where the OPs found that the combination of a diffuser, bounce, and E-TTL threw things off. What ended up happening was that the combination of the bounce and the diffuser led to such a weak preflash reading that the system really went all out on the actual flash, leading to overexposure.

[TeeJay]

Sorry if I'm a bit late on this, but why are you using a + 2/3 FEC, then complaining that your pictures are overexposed. What are they like if you dont use any FEC?

[René Damkot]

Originally Posted by mbze430

and FEC and Aperture controls subject exposure.

Actually, with ETTL, aperture has nothing to do with flash exposure... (unless the aperture is so small the flash isn't powerfull enough )

[René Damkot]

Originally Posted by Jon

What ended up happening was that the combination of the bounce and the diffuser led to such a weak preflash reading that the system really went all out on the actual flash, leading to overexposure.

True. Found this happening to me also... I recently found that in circumstances where this was happening, using FEL gave a blinking flash icon in the VF... You might test that.

[mbze430]

Originally Posted by René Damkot

Actually, with ETTL, aperture has nothing to do with flash exposure... (unless the aperture is so small the flash isn't powerfull enough )

Huh? The basis of flash photography regardless of ETTL is that aperture controls the amount of flash light hitting the film/sensor.

All ETTL does is make an programmed decision on how much output of a flash is required.


Here is a very simple excerise for you. turn off ETTL, and set it to manual flash. Now YOU are in control of flash power. That's all ETTL does. Now, you are at task to make the right decision for the amount of output for which aperture you will use.

[René Damkot]

Originally Posted by mbze430

Huh? The basis of flash photography regardless of ETTL is that aperture controls the amount of flash light hitting the film/sensor.

All ETTL does is make an programmed decision on how much output of a flash is required.

Here is a very simple excerise for you. turn off ETTL, and set it to manual flash. Now YOU are in control of flash power. That's all ETTL does. Now, you are at task to make the right decision for the amount of output for which aperture you will use.

I think I get the basics

I also think we might be meaning the same thing.

However, when using ETTL, the aperture does *not* influence the amount of light hitting the sensor: If the aperture is closed further, ETTL tells the flash to output more. The result is that the same amount of light reaches the sensor. Therefore exposure is the same. (Flash output is different though)
When using manual flash, the flash gives the same output every time, therefore the aperture can be used to regulate the amount of light reaching the sensor (thus exposure)