Okay, I need some help...
I've got a digital camera (Canon Rebel)and I bought a 300mm telephoto lens for it (made by Sigma). Trying to take some photos of local neighborhood birdlife in my backyard. What I see through the viewfinder is an upclose view of what I would hope would be what I capture when I press the shutter button. But for some reason, the captured image appears as if I were still using the default lens instead of the telephoto lens. There's a little switch on the side of the new lens that can be placed in two positions "normal" and "macro". I've tried them both but get the same result.

The links show a picture of approximately what I see through
viewfinder (only much more detailed and sharper) but the next one is what I wind up with.

Can someone please tell me what I'm doing wrong? Is there something wrong with the lens or the camera?

first pic link:
http://www.geocities.com/ericdriver/bjay.jpg

second pic link:
http://www.geocities.com/ericdriver/bigblue.jpg

Your links aren't working due to bandwidth it says. Why not post the image here? Sounds strange to me. : )

The free geocities site runs out of bandwidth on a regular basis. They alot an hourly amount so if unable to visit the link...an hour later all is well. Tried to post the image here but it doesn't fall under the 200k limit. I'm thinking maybe the little switch on the side of the lens might be defective...or maybe Sigma lenses are crappy.

I have two Sigma lenses and have excellent results. I don't have a 300mm, though. I am far from being an expert but with an SLR I don't see how these very different results are possible. What do you see in the LCD after the shot is taken? Maybe someone else has an idea...at this point I wouldn't have a clue. It just doesn't make sense to me.

Looking through the viewfinder(not at the LCD screen) to compose a picture, you are looking through the lens via a mirror inside the camera. (That is what SLR is all about.) The view should be the same except the viewfinder view might be slightly higher and wider than what goes to the image. The difference in the images you showed are drastic and remind me of "playback" of images where some cameras allow a "zoom" view of the captured image on the LCD. There is likely a simple answer but that is the best I can offer without being there. Tom.