Q about lens Focal length and 420EX Flash

[elfyrulz]

how can 420EX E-TTL (Flash Coverage) recognize let say a 50mm lens on a DRebel if it changes the 50mm lens focal length (1.6x) to 80mm?

[Belmondo]

I'm quite sure the flash doesn't know if it's on a film body or a digital body with a 1.6X, 1.3X, or 1.0X crop factor. It zooms for the lens only and doesn't compensate for any naroowing of the field of view. Accordingly, some of the flash is wasted.

[robertwgross]

Yes, better to have some flash wasted than to have too little to cover the frame. Of course, if it were a perfect world, then the flash and the camera would know what is going on.

---Bob Gross---

[DaveG]

how can 420EX E-TTL (Flash Coverage) recognize let say a 50mm lens on a DRebel if it changes the 50mm lens focal length (1.6x) to 80mm?

It doesn't, and that's what everyone else will tell you.

But I would have thought that it would have been an easy fix for Canon. They could just have something in the camera that takes the lenses' focal length information, converts it to 1.6, and then gives this corrected information (i.e. it lies) to the flash. Thus a 50mm lens becomes an 80mm to the flash and it adjust accordingly.

Since this would be camera-born each Canon camera model could have its own conversion identity. I wonder if this is a future fix for the mythical 20D, or maybe Canon (with all of the other problems of E-TTL) just had bigger fish to fry.

[scottbergerphoto]

ETTLII in the Mark II doesn't alter the flash zoom, but it does use distance information provided by Canon lenses so eqipped, to the camera body to use in flash calculations.
Scott