Flash and Exposure Help

[Fiml]

There are certain times when I am shooting pictures at the auction with the 430EX flash I get pictures like this. The first picture is underexposed and the 2nd one is quite a bit better. I didn't change any settings on the camera or flash, I just moved positions.

Any ideas what is causing this?

http://www.funkconsulting.com/300d/problem

-Fiml

[Nuttcraker]

Hi! It could seem very stupid for many people what i'm going to say. But since i've started shooting with ETTL II i've found a huge problem with taking to shots and having the same results. I've read the EOS bible and started exploring the strobist blog.
Results:
1) I only use ETTL II when i want fill in flash (i use FEC a lot)
2) I use manual when i want flash has the main light.
3) I started to use a Sto-Fen Omnibouce difuser and the results with ETTl II get better. (i don´t know why) :)
4)I'm only a rookie probabily others will say that i'm crazy!!

[PAS Photography]

I cant tell for sure but your focus point and metering were taken in different locations. One was on the bright white side 2nd photo, then other on the shadow side 1st photo. That will create a different image all together on top of the ETTL.

[Fiml]

I was shooting in P mode and it's a 300D with the kit lens.

-Fiml

[Tee Why]

Hi! It could seem very stupid for many people what i'm going to say. But since i've started shooting with ETTL II i've found a huge problem with taking to shots and having the same results. I've read the EOS bible and started exploring the strobist blog.
Results:
1) I only use ETTL II when i want fill in flash (i use FEC a lot)
2) I use manual when i want flash has the main light.
3) I started to use a Sto-Fen Omnibouce difuser and the results with ETTl II get better. (i don´t know why) :)
4)I'm only a rookie probabily others will say that i'm crazy!!

I've had similar experience. I used to shoot mainly available light then started to use the flash for fill in via Av Mode and High sync speed with FEC -1 or so.

I tried this set up in a dark place as my main source of light and it was bad. I have to remember that in Av mode, the metering is off of ambient light, so you can get really long shutter speeds even with a flash.

I don't use P mode but I think it defaults to a 1/60 shutter speed and meters off the flash and not the ambient light.

So when using the flash as the main source of illumination, I've started to use the manual mode as well. It's tougher but more rewarding with better results.

[Titus213]

There is a bright light spot under the left chair in #1. Any chance that got in line with your flash? It doesn't take much to shut down the flash in ETTL. In #2 you've moved so that light source is 90 degrees to your left.

[christence]

PAS and TITUS has a very simple right answers to your Q.

[Curtis N]

You can tell by the shadows that the light is coming from the left side of the chairs. It stands to reason that they would look brighter from that side, if the camera's exposure settings were the same.

The prevalence of those shadows, especially in the second photo, indicate that flash did not contribute greatly to the exposure. With that much white in the images, the E-TTL system determined that not much flash power was required for proper exposure. It's common to need +FEC when there is significant white in the frame.

[tim]

Read the book "understanding exposure".