Mini TT1 and 580 EX at different distances

<p>According to everything I've read. The E-TTL system on Canon flashes works by firing a pre-flash, metering it, then setting the flash to the correct power and taking the picture. This is why you can add a shoot-thru umbrella to a speedlight and still get the correct exposure if you are using Canon's infrared system or a wire.</p>

<p>I just purchased the Pocket Wizard FlexTT5 and MiniTT1. I am noticing a change in exposure when <em>I</em> back up and the off-camera flash doesn't. The flash will overexpose. My first thought was, "Well, the camera thinks the flash is 20 feet back with me so it's adding power to the strobe." But then I realized that can't be the case because the system works off a pre-flash.</p>

<p>So, why is the flash power changing and washing out my image? Shouldn't the image be correct regardless of where the camera and flash are positioned?</p>

<p>That's the difference between manual settings and eTTL. My guess is that as you back up, the area of your frame being illuminated by the flash is smaller, and hence your camera is trying to boost the flash power to achieve the overall same level. Hard to tell without seeing images, but that's my guess.<br>

That's one of the reasons why manual flash levels make things so much easier. Once you set the levels you want, it doesn't matter how you frame the shot - as long as your ISO, shutter speed and aperture and flash power are the same you'll get consistent lighting. </p>

<p>You might find this website useful for Speedlite information:<br>

http://speedliting.com</p>