Question about the xti & my 420ex

For a few years, I've owned an Elan7e, 420ex, and a 28-105 f3.5/4.5.

I've just purchased a rebel xti which should arrive any day. Woohoo!

The 420ex & 28-105 obviously work pretty good together because the flash

automatically zooms with the lens.

My question is what happens differently (if anything) when I put that flash &

lens on my spiffy new xti when it arrives? I realize there is the 1.6 crop

factor with the xti. Am I correct in my understanding that this doesn't affect

the flash in any way?

<p>You are correct. If you had certain newer flash models, such as a 430EX, it would understand the crop factor and would zoom accordingly. For instance, if you zoom to 28mm, that's effectively 45mm once the crop factor is taken into account. The 430EX would zoom to the appropriate setting for a 45mm lens; the 420EX would zoom to 28mm. So your 420EX will waste some of its power illuminating things which are outside the field of view.</p>

<p>That's not a big deal unless you're trying to take a shot that demands close to 100% of the flash unit's maximum output. Other than that, you won't have any problems with flash coverage.</p>

<p>The 420's AF illuminator only covers the 7-point layout of your Elan; it doesn't cover the 9-point layout of your XTi. Officially, it covers five of the XTi's 9 points: centre, top, bottom, left, and right. It doesn't cover the four diagonal points. If you manually select an AF point, you'll get AF assist if you pick one of those five, and not if you pick one of those four. If you let the camera choose an AF point on its own, you'll get AF assist, and depending on subject distance and lens focal length, it may actually prove effective on all nine points (or it may not).</p>