What kind of camera are you using it on? A 24 mm on many digital's becomes a 36 mm with the 1.5x magnification factor. With a film camera a 24 mm is a very nice wide, but with a digital you might want something like a 15-18 depending on what is available for your camera.

Bob, I have a 2x teleconverter, a Nikon it does a good job. Make sure it will operate all of your lenses function like auto focus and metering if not you'll be fully manual when your using it. And you lose 2 F stops when using a 2x teleconverter, so a F 2.8 lens would then be a F 5.6
I don't use mine as much as I thought I would, But if you decide to buy one go with quality.

Fisheye lens... I love mine and I am using it more than I thought I would.

Mark