Which zoom lens is best for RebelXT EOS 350D with IS

When you change the zoom, chances are the camera lose focus, and you need to half-press the shutter button again to the camera autofocus.

Its normal behavior to lose focus when zooming in or out.

ERR 01 is a lens communication error. Try cleaning the contacts on the lens and in the mirror box.

ERR 05 is a flash error. It is usually caused because the flash failed to pop up. This can be casued by something as simple as the flash hitting the brim of a 'gimme' cap or impact to the flash or most likely spillage of sticky liquid around the flash and its pivots.

The XT also is notorious for having the bottom right screw of the rear circuit board come loose and short out some function of the camera, or even blow the main fuse or damage the circuit boards.

Sound like a broken ribbon cable in the lens. Needs to be replaced but get a quote as it may be cheaper to replace the lens with a secondhand one.

Clean the contacts on the camera body and lens where they meet with a cotton swab lightly dampened with rubbing alcohol.

If you get err99 with lens then lens diapharm unit goes wrong and its giving er99.
if you getting with body and there is coupleof possiblities.

please descride brifly your camera fault
how and when you geting err99

change your manual settings

Try a different lens just to check out the lens focus sensor. or put it in manual focus.

This means that the communication with the Quantarey lens is not the right one.

You can try in cleaning the lens contacts and the camera contacts with a pencil eraser or a white erase (flip down the camera so no particles get inside the mirror box).

If still you are having problems, then that means the Quantarey lens is defective, and either needs to be service to be repaired, or you will need to get another zoom lens.

Best regards,

Goto any radio shack and get a external memory card reader this will allow you to get your pictures if the camera or cable is defective.

Simga makes lenses to fit several different makes of camera bodies including Canon and Nikon. I'm assuming your Sigma lens has a Nikon mount, if so there are some adapters, but they may not work like you want - not all functions may work properly thru the adapter. For best results you should return or sell the lens and get one with the Canon mount.