Question about lens and flash compatibility

[Luvwine]

I have a 20D and have purchased a Tamron 28-75 (along with a few other lenses) and I have also ordered (from Dell) the 580 flash unit. My question is that I read on another topic someone said that all Canon lenses transfer distance data for E-TTL II which, if I understand it correctly, enables the flash to provide more accurate amounts of light. My question is whether there is an advantage for Canon lenses (like the 24-70L) in this regard over other manufacturer's lenses (like the Tamron). I am happy with the Tamron's image quality thus far, but I still can take it back and so am trying to assuage my concerns.

Best,

STeve O.

[slin100]

Not all Canon lenses report distance data to the camera. Here's a list (http://www.robgalbraith.com/ubbthreads/showflat.php?Cat=&Board=UBB18&Number=217765&Forum= ,,,,,,,,,,,,,,,,,All_Forums,,,,,,,,,,,,,,,,,&Words =&Searchpage=16&Limit=25&Main=215491&Search=true&w here=&Name=210&daterange=&newerval=&newertype=&old erval=&oldertype=&bodyprev=#Post217765). The 24-70L is listed. Furthermore, many non-Canon lenses do report distance data. I haven't checked the EXIF info of my Tamron 28-75, but I believe it does report distance info.

[scottbergerphoto]

When you use a lens that does not transmit distance information to an ETTLII enabled camera like the 20D, the camera continues to use ETTLII. It just doesn't use any distance information. People have been taking flash pictures for many years without it. I just bought my third 550EX instead of a 580EX. I can do without that technommarvel.
Scott

[slin100]

Scott, you are right about ETTLII and its independence from distance information. ETTLII, however, is a function of the camera body; it works with all EX flashes. An ETTLII-capable camera (1D Mk II, 1Ds Mk II, 20D, Elan 7N, Elan 7NE) can incorporate distance information, when available, and use it to regulate a 550EX as well as it can a 580EX.