I wasn't really looking for another camera body, but this Rebel XSi (aka 450D) it was so inexpensive, and in such nice condition, I just couldn't resist it. Yeah, it's an older, entry level DSLR, a little older even than my T3i, but it'll make a nice companion for it. The camera body came to me with a strap, battery, charger, and an 8GB microSD card with an adapter, but no lens. That's okay because I've got a small assortment of Canon EF mount lenses. Just for fun, I stuck a Quantaray 28-90mm zoom lens (rebadged Sigma) on it that would never autofocus on the T3i, and lo and behold, it works on the XSi! I'm not sure what's up with that, but the camera now has a default lens all its own. My other EF mount lenses work perfectly with both camera bodies. I got that lens on eBay, and the seller stated it was untested, as he did not have a Canon camera. When I let him know the autofocus didn't work, but I accepted that was on me, since it was untested, he promptly refunded the purchase price, so I had the lens for just the cost of shipping. That was more than fair, since I hadn't asked for a refund. I'm glad to now have at least some use for the lens. I've only had time to take a few test shots with this camera, enough to confirm functionality. It works, none of the images are worth sharing. I look forward to putting it through its paces in the near future, and will share some of those images when I do.
Glad to here your value grab found renewed life for that old lens. It is a little interesting it works on one but not the other, did it not try to autofocus? It must not be a missing contact, and If the brassing starts to cause communication failure, the impacted lens or body tends to have issues in general.
I'm reasonably certain the problem is with the lens, as I have three other EF lenses, the original 18-55mm kit zoom lens that came with the T3i, a Yongnuo 50mm f1.7, and a Quantaray 55-200 mm, all of which function perfectly on both camera bodies. with this Quantaray 28-90mm lens on the T3i, I can hear the autofocus motor making noise when I depress the shutter button, but the focus never moves. On the SXi, I have determined through further use, that the lens is 'sometimey'. It will focus properly about half the time, and the rest of the time, it just makes noise, as it does on the T3i. I'm not sure what's going on with it, but I'm reasonably certain the lens isn't exactly worth repairing, if it even can be repaired. Still, why it works sometimes on the SXi and never on the T3i, remains a bit of a mystery. I've tried cleaning the contacts on the lens with 90% isopropyl alcohol, but that made very little difference. The contacts themselves do not show excessive wear.
Now that I've had the XSi for a month, I'm finding that I'm gravitating to it more than to the T3i. You'd think the opposite would be true, especially since the T3i has half again more megapixels, 18 vs. 12, but I've hardly shot with the T3i since I got its sibling. Looking at the two side-by-side, it's obviously the T3i is an evolutionary successor to the XSi, and they feel very similar in my hands. I don't know whether it's that having to flip the rear screen out is an extra, albeit simple step, or whether it's because I got a negative vibe off of the guy I bought the T3i from, and having bought the XSi off of eBay, I have no feeling at all regarding its past, but I'm just more comfortable with the XSi, for whatever reason. I just don't understand it.