Canon Rebel eos 100d lenses

[Sentrymx]

I'm new to photography and I'm looking at buying a new lens for my 100d. I am looking at the EF 70-300mm f/4-5.6 IS USM. My question is several parts. 1) is this lens compatable, 2) how do I focus with it in auto? I don't have a zoom button that I found on my camera, and that it's all done manually. And will this affect the auto focus? I really don't want to spend the money on something that I'm not going to be able to take advantage of. Thanks in advance

[Waddizzle]

1)  Yes, any EF or EF-S lens should work with the 100D.

2)  You  focus by putting the lens into "AF" mode, and pressing the shutter button halfway down.

3)  Once a lens is focused on a subject, then it should remain in focus as you manually zoom.  But, not that lens.

What lenses do you already own?  Did you purchase your camera as part of a kit, with a lens?  The 70-300 should work nearly the same as whatever lens was included a camera kit.  Be aware that that particular lens has really bad chromatic aberration, which means high contrast edges in the image can develop purple/green fringing.

    

Notice how the window has a purple fringe?  Better lenses do not have that issue.

[ebiggs1]

"I really don't want to spend the money on something that I'm not going to be able to take advantage of."

Actually that lens was specially designed for the Rebel line of which your SL-1 is part of.  AF and zoom is done on the lens not in the camera.  You adjust the zoom ring by hand. You press the shutter button to make the camera tell the lens to auto focus.

At 300mm, actualy 480mm on a Rebel, you will need to be very steady and use shutter speeds in the higher regions I.E. 1/500 or higher.