Inside low light/flash help please

davidschmaus

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I could use a little help from you guys.

Here is the situation.

Gear:5dII 580exII on camera being bounced

Lens 135l 2.0

So I'm taking some pictures inside today of the family and friends

I have enough light without flash to get me to iso 800 1/125 f2. Put the flash in ettl mode and bounce off of a white ceiling. Everything looks great.

So I want to go between f2 and f4.5 but when I drop below f2 the shutter speed is to slow.

What I want to happen is for the shutter speed stay at 1/125, keep bouncing the flash. If I change from f2 to say f3.5 the iso would change automatically to keep the exposure correct. (unless there is a better way to do it)

Thanks and Happy Thanksgiving...
 
I don't speak Canon, but it sounds to me like either your flash or your body isn't correctly set and isn't getting/expecting the TTL information.
 
When you meter the scene with your camera body, no matter what mode you are in, the camera is reading the ambient light present in the scene and basing the settings/meter reading off that light.

Now when you add flash to the setup the in camera meter is still working of the self same ambient light - it has no idea what the flash light will do to the light in the scene and so ignors it. The flash on the other hand gets the settings data from the camera body and also fires of a preflash when you press the shutter button (its weak and very fast so most times you don't notice it); reads the light given off at the camera settings and then fires a second main burst of light to balance the scene.
Essentially in this mode its just acting as a fill light to fill in shadowed areas rather than being the main light source for the shot.

If you want to make the flash more dominant you have to shift into manual mode (on the camera body) and set the settings to fixed values yourself - and thus when the flash meters to balance for a proper exposure it will have to put out more light and this become the dominant light source.

That is of course when working with ETTL - and is why you have two exposure compensation modes - exposure compensation and flash exposure compensation (for if the flash is missreading the scene or if you want to creatively increase or decrease form the general ETTL reading that it is giving.
 
When you meter the scene with your camera body, no matter what mode you are in, the camera is reading the ambient light present in the scene and basing the settings/meter reading off that light.

Now when you add flash to the setup the in camera meter is still working of the self same ambient light - it has no idea what the flash light will do to the light in the scene and so ignors it. The flash on the other hand gets the settings data from the camera body and also fires of a preflash when you press the shutter button (its weak and very fast so most times you don't notice it); reads the light given off at the camera settings and then fires a second main burst of light to balance the scene.
Essentially in this mode its just acting as a fill light to fill in shadowed areas rather than being the main light source for the shot.

If you want to make the flash more dominant you have to shift into manual mode (on the camera body) and set the settings to fixed values yourself - and thus when the flash meters to balance for a proper exposure it will have to put out more light and this become the dominant light source.

That is of course when working with ETTL - and is why you have two exposure compensation modes - exposure compensation and flash exposure compensation (for if the flash is missreading the scene or if you want to creatively increase or decrease form the general ETTL reading that it is giving.

That is a perfect explanation. Thank you. I did figure it out and was able to change shutter speed to balance flash bounce and ambient light. Worked wonderfully.

Thank you for taking the time. Happy Thanksgiving!
 

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